STORAGE OF LUMBERB y

Raymond C. Rietz

Formerly Research Engineer

Forest Products Laboratory

Forest Service

U.S. Department of Agriculture

(Maintained at Madison, Wisconsin,in cooperation with the University of Wisconsin. )

AGRICULTURE HANDBOOK NO. 531

September 1978

Library of Congress Catalog Card No. 78-600012

Rietz, Raymond C.1978. Storage of lumber. U.S. Dep. Agric., Agric. Handb. 531

63 p.Surveys the most effective current techniques for protecting

the quality of stored lumber. Physical properties of wood which arebasic to the storing of lumber in commerce are explained. Causes ofstorage losses in lumber are discussed. Individual chapters deal withprotection of wood in specific storage environments, such as inyards, at manufacturing plants, or in transit.

KEYWORDS: Degrade, drying, lumber, storage, wood properties

The Forest Products Laboratory is maintained by the Forest Service, U.S. Department of Agricul-ture, at Madison, Wis., in cooperation with the University of Wisconsin.

Mention of chemical treatment in this hand-book does not constitute a specific recommenda-tion; only those chemicals registered by the U.S.Environmental Protection Agency may be rec-ommended, and then only for uses as prescribedin the registration—and in the manner and atthe concentration prescribed. The list of regis-tered chemicals varies from time to time; pros-pective users, therefore, should get currentinformation on registration status from theEnvironmental Protection Agency, Washington,D.C. 20460.

Page Page

Illustration Requests

Requests for copies of illustrations contained in this Handbook should be directed to the ForestProducts Laboratory, U.S. Forest Service, P.O. Box 5130, Madison, Wis. 53705.

PREFACE

“How can I cut down grade loss in my storedlumber?” Forest Service specialists in wooddrying receive similar questions by phone ormail in research centers across the Nation. Butsuch questions cannot be answered without moreinformation. Are we talking about green ordried lumber ? Air dried or kiln dried ? Whatspecies ? How long will the storage period be?What is the intended end use of the lumber?What climate prevails in the storage region?

Questions of lumber storage can lead into thelarger subject of lumber processing, and are oftentoo complex to permit simple answers. Yet suchquestions are of crucial importance becausedegrade and decay during storage are a majorcause of lumber losses. Such lumber wastebecomes intolerable as demands increase uponour Nation’s limited supplies of sawtimber. Theissue demands a comprehensive, practical publi-cation, and thus researchers from the ForestService, U.S. Department of Agriculture, havecompiled this handbook. It should help to fulfillthe Forest Service’s objective of conserving, andthereby extending, our Nation’s forest resources.

Studies have shown that lumber can be stored

with little waste if techniques are applied basedon a scientific knowledge of wood properties.Chapters 1 through 4 of this handbook explainphysical properties of wood which are basic tostoring lumber commercially. The first fourchapters will help answer such questions asthese: Why does wood gain or lose moisture?What conditions must be met to keep kiln-driedlumber dry ? What causes staining, decay, orwarp ? How do hardwoods and softwoods differin their storage properties?

The remaining chapters of this handbook dealwith specific storage situations. Through textand photographs, they give practical details ofthe better handling, packaging, and storageprocedures used in the lumber industry today.Specific problems are discussed, such as themerits and limitations of package wrapping, theprotection of lumber when in transit, and waysof protecting lumber from rain soaking atconstruction sites.

This book also gives recommendations forbetter storage at the end of several chapters,suggestions for additional reading, and aglossary of terms.

CHAPTER 1: PROTECTING LUMBER IN STORAGE

A flatcar piled high with packages of lumbermoves across the Midwest, each package pro-tected in its own jacket of wrapping. Millworkawaits use at a construction site, covered by atarpaulin and resting on small timbers to pre-vent ground contact. Workmen dip packages ofgreen lumber into a fungicide solution prior toshipment. These are examples of effective storageand handling in today’s lumber industry,

When is lumber said to be in storage? Betweencutting and use, lumber undergoes a complexseries of stages in processing and transport.During this time, lumber is frequently stored.After drying and planing, softwood lumber maybe stored before shipping, and then stored againin trucks, railroad cars, or a ship’s hold as itmoves toward a destination. Hardwood lumberis usually dried at the producing sawmill andmoves as rough lumber to the using factories.Finally, lumber may be stored at wholesale andretail distribution yards, at woodworking plants,and at the construction site.

The moisture content of lumber must becontrolled in storage. Moisture changes in lum-ber may at times be the direct cause of gradeloss. For example, the best lumber will be un-suitable for many uses if its moisture contentgoes too high. Also, moisture changes in lumbermay be an indirect cause of deterioration. Forexample, rapid and uneven moisture changescan cause checking and warpage. Also, lumberwith a moisture content of over 20 percent maydevelop stain or decay. (The figure of 20 percentincludes a safety factor; lumber’s moisture con-tent is measured as a percentage by weight ofthe Completely dried wood substance. ) Mostinsect damage to lumber can be avoided if it iswell dried.

Controlling moisture content in stored lumber,as it moves from sawmill to its final destination,

should be the major concern of the processor,agent, and user.

Green and Partially Dried LumberGreen or partially dried lumber usually under-

goes controlled drying when in storage, and isusually stickered and given some protection fromweather (fig.1 ). Green lumber bulk-piled forextended storage during warm weather is indanger from decay, stain, and insect attack. Forthis reason, green lumber should be stickeredfor drying as soon as possible after sawn. Whensuch lumber must remain bulk-piled in warmweather, such as when shipped in the greenstate, it is often protected by chemical treatment(chapter 5).

Dry, High-Grade LumberAt times the maximum moisture content

acceptable for construction lumber is set byindustry practice, and at other times by standardsand codes. Certain industry grading rules, forexample, require that softwood dimension lumberused in the framing of houses be below 19 percentmoisture content. Lumber for use in the heatedinteriors of buildings should properly be stilldrier; its moisture content should not exceed 8percent,

Therefore, those who handle dried high-gradelumber must be careful that it not take onexcessive moisture in storage or transport. Forexample, finished lumber at a construction siteshould not be allowed to undergo soaking fromrain because this would jeopardize its structuralperformance.

The problem is especially acute with kiln-driedlumber to be used in an interior location. If such

lumber becomes wet enough to require redrying,additional labor and expense are required. Also,the lumber will again undergo some degradefrom the drying process and refinishing may berequired.

Dry, high-grade lumber is best protected frommoisture regain when stored as solid packagesunder roof (fig. 2). Closed storage sheds offerthe best protection from moisture regain duringlong-term storage (fig. 3).

Lumber During Transport andHandling

Lumber handling has become mechanized toreduce overall costs at sawmills, distributionyards, factories, and construction sites. Trans-port methods have changed to speed up theloading and unloading of trucks, boxcars (fig.4), flatcars, and ocean-going vessels. The meritsof mechanized handling will diminish if lumber’smoisture content increases during this handling.

High-quality lumber can be protected inseveral ways during transport. Tight boxcarsand dry ship holds can minimize moisture regain.Packages of lumber exposed during transport,such as on open flatcars or tractor-trailer trucks,can be temporarily protected by sheet wrapping(fig. 5). Sheet wraps can also protect lumber atunloading points or during temporary storage atdistribution yards (fig. 6).

Unprotected Lumber OutdoorsHigh-quality lumber will endure for a short

time storage conditions which, if sustained,would cause grade and footage losses. HOW

tolerant any given lot of lumber may be to lackof protection, such as when transported on opentrucks, depends upon the time exposed, theweather, and qualities of the lumber itself.Generally, thicker pieces of wood, such as dimen-sion lumber, will regain moisture more slowlythan thinner pieces, such as nominal l-inchboards. Hardwoods are more resistant to mois-

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ture regain than softwoods, dense woods moreresistant than less dense, and heartwood moreresistant than sapwood.

Benefits of Protective StorageControl of atmospheric conditions during

lumber storage, principally relative humidity,can create a moisture balance in the lumbersuited to its end use. Thus the lumber’s com-mercial quality can actually be improved bystorage.

Dry lumber is usually bulk-piled when storedso that the overdried boards can absorb moisturefrom adjacent underdried boards. Moisture con-tent differences between boards of the lot arethereby lessened. The moisture gradient withinindividual boards also tends to flatten out duringstorage. That is, the difference in moisture con-tent between the shell and core of each board islessened.

Storing dry, casehardened lumber in anatmospherically controlled shed or warehousewill usually result in only slight stress relief.However, if such lumber is stickered in an openshed the regain of moisture by the surfaces willreduce casehardening stresses. At one time thiswas called “tempering.”

High relative humidity alone will not elevatemoisture levels of dried lumber sufficiently tocause serious decay, but may permit some moldto develop. High humidity may also raise themoisture content of kiln-dried lumber enough sothat the lumber must be redried to be used in aninterior service location.

Bulk-piled lumber in bins or unit packagesabsorbs moisture at all exposed faces of the pile.This moisture moves toward the pile interior.Movement is more rapid along the grain, andthe penetration of moisture absorbed at the opencell ends will be the greatest. Moisture enteringthrough the ends of the boards will cause swell-ing, increasing the width and thickness of theends over the rest of the board. Moisture regainby the boards on the top, bottom, and edges ofthe pile increases the moisture content range ofthe lot. Damp outside boards may create prob-lems in subsequent processing.

When l-inch softwood lumber, kiln dried to 8percent or less, is solid piled outdoors under apile roof in humid weather, average moisturecontent can increase at the rate of about 2 per-cent per month during the first 45 days. Anabsorption rate of about 1 percent per monththen may be sustained throughout a humidseason.

Comparable rates for open sheds are about 1percent per month and for closed sheds 0.3percent per month. Total lack of protection, withwetting by rain, will considerably increase theserates.

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CHAPTER 2: MOISTURE CHANGES IN STORED LUMBER

If moisture content in stored lumber becomesgreater than about 25 percent, lumber becomessusceptible to decay, stain, or insect attack.Furthermore, uneven wetting or drying of lum-ber will cause warp. Grade loss due to moisturechange can be prevented, but methods differ forgreen, air-dry, and kiln-dry lumber.

Green lumber loses moisture to the air duringstorage, and if dried unevenly will warp. Stick-ering green lumber prevents warp by allowingair to circulate through the pile. Moisture canthen evaporate evenly from all faces of theboards, and uneven shrinkage stresses areprevented.

Kiln-dry lumber tends to take on moisturefrom the air; storage procedures should thusminimize or prevent moisture regain. If kiln-drylumber regains much moisture, the expense andeffort of the kiln-drying process may have beenwasted.

Techniques for controlling moisture move-ment in lumber fall into three categories:(1) determining the moisture content of storedlumber; (2) predicting and, in some instances,controlling moisture loss or regain; and (3) cal-culating the dimensional changes in lumbercaused by changes in moisture content.

Wood Properties and MoistureMovement

Wood will either lose or absorb moisture whenexposed to certain conditions of temperature andrelative humidity; this property is known ashygroscopicity. Changes in moisture contentcause wood to shrink and swell, creating problemsduring processing and final use.

Free Water and Bound Water

The moisture in freshly cut (green) lumberis often called sap. Sap is simply water withcertain materials in solution. Water in greenwood exists in two forms: As liquid in the cellcavities, known as “free water,” and as moisturein the cell walls, known as “bound water.”

The moisture content of wood is the weight ofthe water which wood contains divided by the

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weight of the completely dried wood substance.Wood’s moisture content is always expressed asa percentage. Average moisture content of livingtrees will vary by species from about 30 percentto more than 200 percent (table 1).

Green moisture content of wood from differ-ent locations within the same tree can varyconsiderably. For instance, in softwood speciesgreen moisture content for sapwood is muchhigher than for heartwood. Green moisture con-tent of sapwood and heartwood does not differso much in hardwoods; some green hardwoodswill even have a higher moisture content forheartwood.

Growing conditions of the individual tree willalso affect green moisture content. These condi-tions include soil characteristics, climate of thelocale, and, in some instances, the altitude of thegrowth site.

Fiber Saturation Point

When green lumber dries, free water incavities of the surface cells will leave first. Nobound water will leave a cell until all the freewater has evaporated. Wood’s moisture condi-tion when all free water has evaporated but thecell wall remains saturated is called the fibersaturation point (FSP). In general, the FSPprevails at a cell moisture content of about 30percent; it may vary to some extent from speciesto species. When the cell walls are dried belowthe FSP, shrinkage begins. As adjacent cells inthe wood dry below the FSP, changes in thephysical and mechanical properties of the woodoccur.

Moisture Diffusion Characteristics

The rate at which lumber loses or regainsmoisture is directly affected by the moisturediffusion characteristics of the particular wood.Understanding moisture movement in wood canhelp avoid grade losses caused by uneven mois-ture changes, such as warp, checking, andsplitting.

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Moisture diffuses through wood from zonesof higher to zones of lower moisture content.Thus, when lumber is drying the moisture in thewet interior of a board moves towards the driersurface. If dry lumber is exposed to high rela-tive humidity or wetting while in storage,moisture diffuses from moist surfaces of theboards to the drier interior. The greater thedifference in moisture concentration, the morerapid will be the diffusion rate in both resorptionand absorption.

The moisture diffusion rate varies with woodtemperature. Cold wood in storage respondsmore slowly to changes in atmospheric condi-tions, but moisture will move more rapidly inwarm wood.

Moisture diffusion in wood is also influencedby the wood’s specific gravity. In general, themoisture diffuses more rapidly in the lighter,low specific gravity woods than in the heavier,high specific gravity woods. This accounts forfaster moisture regain by softwoods in situa-tions where dry lumber is stored under humidconditions.

Moisture content changes more rapidly inpermeable than in impermeable woods. Thus, thesapwood of most species dries faster than theheartwood and, conversely, regains moisturemore rapidly.

Equilibrium Moisture Content

Wood at or above the fiber saturation point,such as green wood, will lose moisture whenexposed to any relative humidity below 100 per-cent. Also, totally dry (ovendried) wood willabsorb moisture when exposed to any relativehumidity except zero. At a constantly maintainedtemperature and relative humidity, any woodwill reach a point where it neither loses norgains any moisture. When wood is in moisturebalance with the relative humidity of the airsurrounding it at a given temperature, the woodis said to have reached its equilibrium moisturecontent ( EMC ).

The relationship between wood EMC and thetemperature and relative humidity of air isshown in figure 8. The graph shows that attemperatures below 120° F (49° C) the EMCof wood is closely related to the relativehumidity.

Air temperature is of secondary importancewhen. determining EMC. For example, at 20percent relative humidity and a dry-bulb tem-perature of 40° F (5° C), the wood EMCcondition is about 4½ percent. Elevating thetemperature 60° F (or 33° C) would reduceEMC by only half a percent (to 4 pet).

On the other hand, if the relative humidityvaries from low to high at the same temperature,

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the EMC will change considerably. For example,at 700 F (210 C) and 20 percent relativehumidity, the EMC is just under 4½ percent;but at the same temperature and 80 percentrelative humidity, the EMC is 16 percent.(Determining EMC so as to control moisturechanges in stored lumber will be explained laterin this chapter. )

Determining Wood’s MoistureContent

The moisture content of wood is expressed asa percentage by weight of the dry wood sub-stance. Moisture content is usually determinedby one of two methods: Ovendrying or use ofelectric moisture meters. The ovendrying methodinvolves determining the weight of the woodsubstance after complete drying in an oven (i.e.,until constant weight is attained). Ovendryinghas the advantage of being the more accuratemethod, but is time-consuming and requires thata piece be cut from the wood to be tested.

Electric moisture meters give rapid andreasonably accurate readings throughout therange of 7 to 25 percent moisture content, butare subject to error if improperly used. Somemodels do not damage the wood being tested;

others require that needlelike electrodes bedriven into the wood.

Wood that contains large amounts of volatilessuch as pitch or preservatives must be tested formoisture content by a distillation method.

Ovendrying Method

The ovendrying method requires that a crosssection be cut from the board at some distance,say 18 inches, from an end. This cross sectionmust remain in the oven for at least 12 hoursand usually more. The ovendrying method isaccurate throughout the whole range of moisturecontent. It consists of the five following steps:

(1) Cut a cross section about 1 inch thickalong the grain.

(2) Immediately after sawing, remove allloose splinters and weigh the section.

(3) Put the section in an oven maintainedat a temperature of 217.4° ± 3.6° F (103° ±20 C), and dry until a constant weight isattained.

(4) Weigh the dry section to obtain theovendry weight.

(5) Subtract the ovendry weight from theinitial weight, and divide the difference by theovendry weight, multiplying the result by 100to obtain the percentage of moisture in thesection. This is the moisture content of thesection and is usually assumed to be repre-sentative of the board. The formula for thiscomputation is:

Moisture content in percent

Balances used in weighing specimens formoisture content determinations include thetriple-beam balance (fig. 9) and the pan-type ortorsion balances. Where a considerable numberof specimens are weighed in and out of thedrying oven, a direct-reading automatic balanceis very convenient.

The oven used for drying the moisture sec-tions should be large enough to accommodate a

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moisture content and the dielectric loss factor of

number of specimens, with room to providespaces between them. The temperature of theoven needs to be controlled with a reliablethermostat at a setting within the limits of217.4° ± 3.6° F (103° ± 2° C). Excessive tem-peratures will char the specimens, introducingerrors in the moisture analysis. Too low atemperature may not evaporate all the moisturein the specimen. The oven should be well venti-lated to allow the moisture being evaporated toescape.

Electric ovens are most generally used. Whenthe volume of specimens to be ovendried daily isrelatively small, a natural-circulation electricoven is adequate. Some ovens contain fans tocirculate the heated air; when large numbers ofspecimens are being ovendried, electric ovenswith fans are recommended.

Microwave ovens are sometimes used to drythe sections. Drying time is reduced to minutes,but destructive distillation of the wood mayintroduce errors in moisture content calcula-tions. With experience in operating the micro-wave oven, however, these errors can be avoided.

Electrical Methods

Electric moisture meters are being extensivelyused, particularly the portable or hand meters.Two types, each based on a different funda-mental relationship, have been developed:(1) The resistance type, which uses the rela-tionship between moisture content and directcurrent resistance (fig. 10) ; and (2) the dielec-tric type, which uses the relationship between

the wood (fig. 11).Resistance-type moisture meters are wide-

range ohmmeters. Portable, battery-operatedmodels are available. Most models have a direct-reading meter calibrated in percent for onespecies; the manufacturer provides correctiontables for other species. The manufacturerusually provides a temperature-correction chartor table when tests on wood warmer than 90° F(32° C) or cooler than 80° F (27° C) are made.

Electrical resistance of wood decreases aswood warms and increases as it cools. A rule-of-thumb temperature correction is to subtract 1percent moisture content from the meter read-ing, corrected for species, for every 200 that thewood temperature is above 800 F. Add 1 percentfor every 20° that the wood is below 80° F.

Resistance-type meters are generally suppliedwith pin-type electrodes that are driven into thewood being tested. The most common consist of

their mounting chucks. Long, two-pin electrodeswhich have insulated shanks except for the tipare also available for use on lumber thicker than

When lumber with a normal drying distribu-tion is tested, valid estimates of the averagemoisture content of the cross section are obtainedby driving the pins deep enough in the lumberso that the tip reaches one-fifth to one-fourththe thickness of the board. If the lumber is re-gaining moisture or the lumber surface has beenwetted, the meter indications are likely to bemuch higher than the actual average moisturecontent. In this case, insulated shank pins shouldbe used.

The useful range of resistance-type moisturemeters is from about 7 to 25 percent moisturecontent. Meter readings greater than 30 percentcan only be considered as gross approximationsof the real moisture content of the wood. Whenthe electrodes are withdrawn, care is essentialto prevent pin breakage or bending.

The dielectric moisture meter uses surfacecontact-type electrodes. The electrode is anintegral part of the instrument (fig. 11). Thelumber being tested is penetrated by the electricfield radiating from the electrode about ¾ inchinto the wood, so that thicknesses to about 1½inches may be tested. The moisture content ofthe surface layers of the lumber, however, has

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a predominant influence on the meter readingsbecause the electric field is stronger nearthe electrode. The roughness of the lumber andthe electrode design may also influence meterreadings.

The effect of wood temperature on the dielec-tric loss factor and dielectric constant is notwell understood, so temperature correction chartsor tables are not provided with dielectric meters.The manufacturers do, however, provide speciescorrection tables for converting the meter scalereading of the instrument to moisture content.

The useful range of the dielectric moisturemeter is from O to 25 percent moisture content.

Predicting and ControllingMoisture Change

Being able to derive the equilibrium moisturecontent (EMC) of lumber in storage can bevery useful to those responsible for the storagefacility. Average temperature and relative hu-midity of a locale can be used to determine theEMC, and thus the eventual moisture contentwhich lumber will attain when stored outdoorsin that locale.

Furthermore, calculations involving EMC canbe used to determine the temperature requiredin a heated, closed shed to attain a desiredmoisture content in lumber stored there.

Determining EMCThe EMC may be determined for lumber at

any ambient temperature and relative humidity.Where atmospheric conditions are constant, suchas in heated or air-conditioned sheds, tempera-

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(10° C) and 80 percent relative humidity isabout 3.5 grains per cubic foot (fig. 13). At thisabsolute humidity and a wood EMC value of 7percent, the dry-bulb temperature is about 75° F(25° C). This means that if the closed shedair is heated 25°—from 50° to 75° F ( 10° to24° C) —and circulated around the dry lumber,moisture regain by the lumber is prevented.

The heating in a closed storage shed may beregulated manually or with automatic controlequipment. Because the EMC is far more de-pendent upon humidity than upon temperature,a humidistat rather than a thermostat is thebest automatic system to use. (See “Closed,

humidity but may increase the temperature toan uncomfortable level for workers inside.Assume that the outdoor temperature is 90° F(32° C) and the relative humidity is about 78percent. The EMC condition of the outdoor airis then 15 percent. To attain a 7 percent woodEMC condition in the shed requires a tempera-ture increase to 1150 F (46° C). But workmenmay object to working in that warm a shed.

One solution is air-conditioning, but the in-creased costs may not be justified. However, atsome woodworking plants, year-around air-conditioning is installed to control the tempera-ture and relative humidity where wood isprocessed. Storage rooms for kiln-dry lumberare often included in these temperature- andrelative humidity-controlled areas.

Predicting Dimensional Changes in Wood

When the cells in the surface layer of a boarddry below the fiber saturation point (FSP) —that is, below about 30 percent moisture con-tent-the cell walls shrink. This shrinkage isrestrained by the wet core of the board, yet thestresses in the surface layer caused by cell-wallshrinkage can be sufficient to squeeze the wetcore. Thus, a slight overall shrinkage of theboard can be observed although its averagemoisture content is still considerably greaterthan 30 percent. For most practical purposes,however, the shrinkage of wood is considered asbeing proportional to the moisture lost below 30percent.

Shrinkage Characteristics

The shrinkage of wood varies with speciesand with the orientation of the cells-tangential,radial, or longitudinal (fig. 14). Shrinkageacross the width of a board sawed tangentiallyto the annual growth rings (plain sawed) isabout twice as much as in a board sawed radially,or parallel to the rays (quartersawed). Longi-tudinal shrinkage or shrinkage in length isgenerally very small (0.1 to 0.2 pet of the greendimension).

Reaction wood, such as compression wood insoftwoods and tension wood in hardwoods,shrinks considerably more in the longitudinaldirection than normal wood. Juvenile wood foundnear the pith of the tree also has an appreciablelongitudinal shrinkage. Table 2 gives the totaltangential and radial shrinkage values for manycommercial species. The values are expressed asa percentage of the green dimension. Thusa plain-sawed board that is 10 inches wide whengreen, of a species having a 10 percent total

tangential shrinkage, will shrink about 1 inch inwidth when dried to O percent moisture content.

Dimensional Change Formula

The values of table 2 can be used to calculatethe radial or tangential dimensional change ofwood in going from one moisture content con-dition to another. The wood species, essentialgrain pattern, present dimension, and moisturecontent must be known to calculate the shrinkageor swelling that will occur if the item changesmoisture content.

The formula is

ST and SR = the total tangential or radialshrinkage values.

Neither the initial nor the final moisture con-tent values can exceed the FSP. Examples of theuse of this formula to determine dimensionalchanges follow:

Example No. I. —Determine the width of theends of packaged flat-grained oak flooring stripsmachined to 2¼ inches at a moisture content of6 percent, then stored in a warehouse wheremoisture pickup causes the exposed end grain toreach 12 percent moisture content. Some piecesare of northern red oak and some of southernred oak. Because the pieces are flat grained, thetotal tangential shrinkage values of 8.6 percentfor northern red oak and 11.3 percent forsouthern red oak are used (table 2). A value of30 is used for FSP. The initial moisture contentis 6 percent and the final moisture content is 12percent. The dimension at the initial moisturecontent is 2.25 inches.

‘ Twenty-two percent is used for redwood, northernwhite-cedar, and western redcedar.

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Substituting in the formula will yield thenorthern red oak dimensional change:

The positive value denotes swelling. The ends ofthe pieces of strip flooring are 0.041 inch widerthan the inner portion due to moisture absorptionby the end grain.

The total tangential shrinkage value forsouthern red oak is greater than northern redoak; substituting in the formula:

The endwise moisture absorption gradient withits accompanying swelling may create difficultiesin the installation of the flooring.

Example No. 2.—Determine the shrinkage inwidth of a nominal 2- by 8-inch Douglas-firplain-sawed joist machined to a width of 7½inches at a moisture content of 19 percent andthen dried to 12 percent moisture content in aretail lumberyard. In this example, FSP = 30,MI = 19, MF = 12, D = 7.5, and, from table 2,ST = 7.6 percent. Substituting in the formula:

The width of the joist at the lower moisturecontent is 7.500 — 0.137 inches or 7.363 inches.

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CHAPTER 3: EFFECTS OF CLIMATE ON LUMBER STORAGE

Air temperature, relative humidity, and rain-fall of the ‘storage region affect procedures toprotect lumber stored outdoors.

Relative HumidityRelative humidity has a much greater effect

on wood’s equilibrium moisture content (EMC )than does temperature (fig. 15). That is, themore humid a region, the more rapidly dry lum-ber will take on moisture when yarded there.Seasonal estimates of the average wood EMCfor a region can be helpful when trying to con-trol moisture change in lumber stored outdoors.Such estimates are supplied later in this chapter.

Storage methods to retain low moisture con-tent in kiln-dry lumber will differ sharplybetween humid regions such as Florida and dryregions such as New Mexico. Likewise, storagerequirements may differ from month to monthin regions where average relative humidityvaries considerably with seasons, such as ininland California. Procedures explained in thishandbook should be qualified in terms of averagerelative humidity of the storage region, especiallywhere relative humidity differs greatly from thenational average.

TemperatureAir temperature affects stored lumber because

warming speeds up moisture diffusion and thusincreases lumber’s rate of moisture change.Thus, if moisture differences between boards inthe lot need to be reduced, storage of lumber inwarm air temperatures is advantageous.

Warm temperatures also increase the hazardof fungal infection in stored lumber. All lumberis practically immune to fungal infection below30° F (–10 C). When green lumber is solidpiled, mold, stain, and decay fungi will grow attemperatures from 400 to 1000 F (about 50 to38° C) with rate of attack increasing rapidly athigher temperatures in this range. Dipping orspraying freshly sawed lumber with an approvedfungicide appreciably reduces the likelihood of

fungal growth. If, however, treated lumber isheld too long in the bulk pile in warm weather,fungi can grow rapidly (chapter 5).

RainfallWhen lumber is stored outdoors with good

protection, rainfall does not greatly affect itsmoisture content. Bulk-piled green lumber isoften temporarily stored outdoors unprotectedbefore stacking for air drying or kiln drying.Some wetting of green lumber is not consideredhazardous. If, however, green lumber has beentreated with a fungicide for extended greenstorage or shipment, protection from rain isneeded. Rain would leach the chemicals from theexposed boards.

Bulk-piled dry lumber should be protectedfrom rain, preferably in storage sheds. Redryingbulk-piled lumber that has been wetted by rainis difficult. Bulk-piled lumber that was thoroughlysoaked must be stickered before it is redried,and redrying will bring further shrinkage anddrying loss. Also, if rain-soaked lumber increasesits moisture content to 20 percent or more, fungimay grow, causing stain and decay.

Average EMC Conditions byRegion and Season

The estimated wood EMC conditions forspring, summer, fall, and winter for the UnitedStates are given in table 3. Average tempera-tures and relative humidities reported by theWeather Bureau for the four seasons have beenconverted to wood EMC values. The States ofAlaska, Washington, Oregon, California, andTexas are divided into coastal and inlandregions; Arizona into a lowland and a highlandarea; and Hawaii into windward and leewardlocations.

Five designations—arid, dry, moist, damp, andwet—are arbitrarily established for classifyingthe average wood EMC conditions of the outdoorair. In a specific location, actual EMC valuesmay differ from the table 3 values in some years.More localized EMC values can be determined

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from average temperature and relative humidityvalues supplied by the closest major weatherstation.

During the spring months, Arizona is desig-nated arid. The rest of the Southwestern States,except for Texas and California, fall into the drydesignation. The coastal areas of Texas andAlaska are designated wet. The remainder ofthe country is divided almost equally betweenthe moist and damp designations.

During the summer months, the States westof the Mississippi River are much drier thanduring the spring months. East of the MississippiRiver, conditions are a trifle damper than in thespring months. Florida is the only Eastern Staterated wet. During the same season, the SouthernStates, Lake States, and the Atlantic coastalareas are generally designated damp. The GreatPlains States and the Northeast generally fall inthe moist category.

Fall is considerably damper than spring andsummer throughout the whole country, Many ofthe Western States shift from arid to dry in fallwhile some even change from dry to moist. Theregions rated moist and damp change littlebetween fall and other seasons.

For the United States as a whole, the weatheris damper during the winter months than in thefall. No States are arid in winter and only threeStates are designated dry. The greatest changeoccurs in States west of the Rocky Mountainsand south of the Great Lakes. A considerableportion of the Pacific Northwest shifts to thewet designation in winter.

The climate of Alaska is generally wet through-out the year. All parts of that State exceed anEMC of 15.0 percent, except that the inlandregion in the spring and winter has EMC condi-tions just under 15.0 percent.

The climate of Hawaii is relatively moist over-all, but varies widely depending on location inthe State. The hot, humid climate of Puerto Ricoplaces this island in the wet designation much ofthe year despite localized variations.

The potential of a locale for lumber drying ormoisture regain is established by its averagewood EMC values. Rate of moisture change,however, is influenced by the temperature of thestorage location. Local conditions may shift theaverage EMC conditions to some extent. Weatherdata published in local newspapers can be usedto determine the local EMC conditions.

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CHAPTER 4: TECHNIQUES FOR STORING LUMBER

Between cutting and use, lumber will probablybe stored a number of times: At the sawmill,during transport, at lumberyards, and at theconstruction site. During each of these storageperiods, the goal of the manager or supervisorshould be to minimize grade and footage losses.

At sawmills, green lumber is stored beforebeing stacked for air drying or kiln drying, orbefore shipment. Softwood sawmills store roughlumber before finishing in the planer mill. Oncethe lumber has been planed it is often storedindoors, but outdoor storage with protectivepackaging is also becoming common.

At hardwood sawmills, green lumber is usuallynot stored long before snickering because of thedanger of fungal staining. Air-dry rough hard-wood lumber is usually bulk-piled and stored inopen sheds, or outdoors under a protective cover.Kiln-dry rough hardwood lumber usually awaitsshipment or factory processing in closed sheds.

Green, rough lumber is seldom protected whentransported from sawmill to drying yard. How-ever, dry lumber, whether rough or finished, isusually protected by tarpaulins during trucktransport, by waterproof paper packaging duringflatcar shipment, or by being loaded into tightboxcars (fig. 16).

Dry lumber at woodworking plants is mostoften stored in sheds, although unit packages ofsoftwood lumber in waterproof wrap are storedoutdoors for limited periods (fig. 17). Lumberstored at construction sites is seldom adequately

protected, but should be. By scheduling lumbershipments the contractor can at least keep thevolume of exposed lumber to a minimum untilthe roof of the structure is installed and lumberstorage space in the building becomes available.

Storing Lumber OutdoorsLumber is often stored outdoors, sometimes

because shed or warehouse facilities are notavailable. Unprotected storage outdoors is satis-factory for such lumber items as small timbersand lumber for less exacting uses, although pre-cautions to prevent stain, decay and insect in-festation may be necessary. But kiln-dry lumberstored outdoors without protection will show arapid increase in moisture content. Rain wettingof any dried lumber is detrimental and tends toincrease the degree of checking.

Protection against rain is more important forsolid-piled lumber than for stickered packages,because rainwater cannot evaporate readily fromsolid piles. Furthermore, rain that penetratesbulk-piled lumber may in time increase themoisture content of the wood to a point wherestain and decay fungi can grow. Some rain islikely to penetrate outdoor piles of lumber de-spite protecting pile covers, Consequently, ex-tended outdoor storage of dry lumber, especiallyin solid piles, is hazardous.

If green or partially dried lumber is to bestored outdoors for some time, the processes of

yarding lumber for air drying are involved andthe recommendations in Agriculture Handbook407, “The Air Drying of Lumber,” apply.

Temporary Protection

Plastic-coated paper wrap for the unit pack-ages of lumber (fig. 17) will adequately protectkiln-dried softwood lumber under short-termstorage conditions such as the following: Long-haul transport on flatcars; interim storage atdistribution centers; and short-term outdoorstorage, such as at construction sites.

But coated paper wrapping should not beconsidered a substitute for storage sheds whenlong-term storage of dried lumber is involved.The wrap can deteriorate during long-term ex-posure. The fragility of paper wrap must alsobe taken into account during handling. At theleast, lumber which is stored outdoors for anylength of time in a protective wrap should beperiodically inspected, and rips in the wraptaped or otherwise mended.

Dilapidated wrapping that holds rainwatermay increase moisture regain more than if thelumber had no protection. To avoid such waterretention and to avoid tearing during forklifthandling, the bottom of wrapped packages isoften left uncovered. However, dampness fromground water can enter such packages if notenough ground clearance is provided by the pilefoundation. The safe storage period with water-proof wrap will depend on the weather (chapter3), and upon the rate of wrapper deteriorationdue to exposure, mechanical handling, or damageby birds and animals.

Tarpaulins are often used for protecting bulkeddry lumber temporarily stored outdoors. Water-repellent-treated canvas, single-film polyethylene(fig. 18), and laminated polyethylene filmswith scrim reinforcing are used as protectivetarpaulins.

Lumber Storage YardsThe outdoor storage yard can be located at

the sawmill, the wholesale or retail lumberyard,the custom kiln-drying plant, or the woodwork-ing factory. Conventional air drying is often

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practiced at such a yard (fig. 19), Thus the bestlocation is on high, level ground which is welldrained and not obstructed by trees or buildings.A yard surface that is smooth and firm, par-ticularly along the alleys, facilitates movinglumber packages. The yard layout should beoriented to the prevailing winds to accelerate thedrying of stickered lumber. Vegetation can becontrolled with weed killers. Routine maintenanceshould remove debris, which harbors stain anddecay fungi and poses a fire hazard.

An air-drying yard for storing stickered lum-ber packages is often laid out so that rows ofpiles run between main alleys. The rows may beshort or long depending upon the amount oflumber to be stored in each row. A number ofrows between cross alleys constitutes a lumberstorage block.

A line-type storage yard may be used if alarge amount of lumber is stickered for air dry-ing and accessibility is highly important. Withthis type of layout, two lines of pile foundationsare built between two main alleys to accommo-date packages of lumber (fig. 20). All piles ofpackages are accessible from the main alleys. Themain alleys in both row-type and line-type fork-lift yards are usually 24 to 30 feet wide. Thecross alleys are often as much as 60 feet wide toseparate the blocks and check the spread of fire.A lumber storage yard which is completelypaved facilitates lift-truck operation and allowseasier yard rearrangement with changes inlumber inventory.

The main alleys are oriented in terms of theyard site available. In a forklift yard of stickeredlumber, particularly a line-type yard, the move-ment of air through the packages is stimulatedby placing the main alleys parallel to the pre-vailing winds. Where rainwater evaporation orsnow and ice melt are important considerations,however, the main alleys are usually orientednorth and south.

Use of Pile CoversHigh-grade lumber stored in the yard, whether

solid piled or stickered, should be protected fromthe weather. Lumber exposed to alternate wettingand drying will check, split, warp, and discolor.Piles of stickered lumber in the storage yardcan be provided with pile covers as in conven-tional air-drying yards (fig. 19). Pile covers ofvarious designs and materials are placed on thepile’s top package before lifting that packageinto place.

Panel-type pile covers can also be used to roofstored, solid-stacked packages of rough orfinished dry lumber. The covers must be rain-tight and project beyond the pile ends and sidesto prevent rain entry into the bulked packages.

Piling MethodsWhether lumber should be solid piled or

stickered depends upon its moisture content,intended use, and estimated duration of storage.Lumber with an average moisture content of 20percent or more which is to be held in storage

for some time, particularly in warm weather,should be stickered as for conventional air dry-ing. Such lumber is likely to seriously deteriorateif held very long in a solid pile. Mold and stainwill develop, followed by decay.

If the moisture content of stored lumberaverages less than 20 percent, mold, stain, anddecay fungi will not grow. The intended use ofthis lumber, however, may be such that furtherdrying is required. If so, snickering for outdoorstorage may effect further drying dependingupon initial moisture content of the lumber andthe prevailing climate.

Kiln-dried lumber will tend to regain moisturewhen stored outdoors, particularly during cool,damp periods, Thus solid piling may be prefer-able to snickering. But kiln-dry lumber which issolid piled must be protected from rain.

Pile FoundationsA pile of air-drying lumber requires some type

of foundation to insure ample ground clearancefor good ventilation under the pile. A line-typeforklift yard will have permanent foundations(figs. 19, 20), whereas a row-type yard can haveeither permanent or portable foundations (fig.21), Foundations should be strong, resistant todecay, and high enough to provide a clearance ofat least 12 to 18 inches between the lumber andthe ground. More clearance is needed if the yardis not paved.

In a line-type yard, posts or piers supportstringers of timbers or railroad rails. Thestringers are parallel to the lumber. Crossbeamsplaced on the stringers support the lumberpackages.

In a row-type yard, posts on footings supportthe stickered packages at the outer sticker tiers.A removable foundation is used to support thecenter of the pile to prevent sagging and permitforklift entry (fig. 21).Storing Solid Packages

Unit packages of bulk-piled lumber intendedfor forklift truck or carrier handling are oftenbuilt with tie strips to keep the edge boardsfrom falling off. In addition, the unit package isoften strapped at two or more points to make acompact, rigid-handling parcel. The tie stripsare also used to separate quantities of lumberwithin the package.

The tie strips should be vertically alined if anumber of layers are stripped, and should also bealined with the supporting beams of the pile

foundations or carrier bunks. Packages in thepile should be separated by bolsters—usually 4by 4’s-alined with the supporting beams.Sagging is thereby prevented.

The size of the unit-handling package is de-termined by the weight-carrying capacity of thelumber-handling equipment being employed.When forklift trucks are used, the height thatpackages can be piled is limited by the reach ofthe fork-elevating mechanism, seldom more than30 feet. Piles higher than this of 4-foot-widepackages tend to tip over unless tie bolsters areused. Excessive loading may crush tie strips orboards in the lower levels of the pile.Storing Stickered Packages

Stickered packages are seldom strapped be-cause they do not have the stiffness that a solidpackage exhibits, A stickered package must bewell supported by a good foundation that hassupporting crossbeams at most of the stickertiers. Bolsters between the packages in the pileshould be in good vertical alinement with thesticker tiers to effectively restrain warp.

Storing Lumber in ShedsStorage sheds offer lumber the best protection

from weathering, and also eliminate the expenseof making, storing, handling, and maintainingpile covers. Losses in grade and footage throughoutdoor air drying have stimulated an increasedinterest in using open sheds for drying. Opensheds provide permanent roofs, and can also beused for storing air-dry lumber. Further modi-fication-by closing up open sheds, installingfans to create air circulation around the storedlumber, and adding heat-can appreciably lowerthe moisture content of stored lumber.

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Open Sheds

An open shed is a roofed lumber storage yard.All lumber items except those kiln dried tomoisture contents of less than 12 to 14 percentcan be stored in open sheds. The atmosphericconditions within an open shed are substantiallythose found outdoors. If the outdoor air cancirculate through and around stickered packages,the lumber will dry to as low a value as it doesin an exposed air-drying pile. The drying periodin an open shed is usually shorter and the lumberbrighter than if stored outdoors because wettingand rewetting are prevented.

Bulk-piled, kiln-dry lumber will regain mois-ture with extended storage in an open shed,although more slowly than if stored unprotected.Increase will be greatest in the outer tiers of asolid pile. For example, surfaced boards of 1-by8-inch kiln-dry Douglas-fir averaged 6.9 percentmoisture content when put in storage at awestern sawmill. Moisture content of the boardsincreased by 3.4 percent when stored for 1 yearas a carrier package in an open shed. The twoouter tiers of boards in the five-tier packageincreased 3.8 percent in moisture content, thecenter tier 2.7 percent (fig. 22).

A shed maybe open on all sides or on one sideonly (fig. 23). Where unit packages are handledby forklift truck, access to the shed is providedby one or two open sides. The rows of piledpackages may run across the shed in bays be-tween the roof supports. Where lumber is han-dled manually in and out of bins, as at someretail lumberyards, a driveway between the opensheds provides access. The roofs of these opensheds usually extend far enough over the drive-way so that trucks can be loaded and unloaded inrainy weather.

Open sheds at the larger lumber-producingsawmills are usually paved for forklift trucksand other carrier vehicles. Cranes operatingwithin open storage sheds for dry, rough lumberare generally of the monorail or bridge type, andpile foundations are built up on the gradedground. At small sawmills and retail lumber-yards, open sheds are not always paved, althoughthe roadways may be graded or graveled. Openstorage sheds at wholesale lumberyards andwoodworking factories usually have paved floorsand driveways.

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Figure 22.—Change in the average moisture content ofsurfaced 1- by 8-inch Douglas-fir boards stored as acarrier package in an open shed.

Closed, Unheated ShedsClosed, unheated sheds (fig. 24) are generally

used for storing kiln-dry lumber. The objectduring storage is to maintain the percent mois-ture content attained by the drying process.Thus, lumber should be solid-piled in closed,unheated sheds, with only enough tie strips tostabilize the package or to designate species,quantities, grades, or items within it.

Kiln-dry lumber stored in an unheated, closedshed will absorb some moisture, but less thanif it were stored outdoors. For example, l-inchsouthern pine boards in a solid pile went from7½ to 10¼ percent average moisture contentduring 1 year of storage in a closed shed. Similarlumber which was solid-piled outdoors for thesame period reached a moisture content of 131,4percent.

Storage in an unheated, closed shed will alsodecrease the moisture gradient in stored lum-ber—that is, the difference between the mostmoist and least moist boards in the package. Forexample, solid-piled packages of rough 1- by6-inch kiln-dry clear Douglas-fir boards werestored in a large, unheated storage shed for 1year. Curves showing the range of moisture con-tent before and after the storage period are seenin figure 25. The range in the lumber’s moisturecontent before storage was about 20 percent; itwas 13 percent after storage. Although therange was reduced, the reduction was generallyat the expense of the dry boards in the unitpackages. Ninety-five percent of the boards inthe packages underwent an increase in moisturecontent.

The roof and walls of a closed shed absorbsolar radiation and in turn heat the air inside.The warmed air, however, tends to remain in theupper parts of the shed. To be effective in low-ering the equilibrium moisture content condi-tions around the stored lumber, the warm airmust be moved downward and circulated byfans. Forced circulation, even without additionalheating, is beneficial. Forced circulation, togetherwith an additional source of heat, will convert aclosed, unheated shed to a closed, heated shed.

Closed, unheated sheds for lumber storageshould be floored or paved if the handling equip-ment operates on the floor surface. If the closedshed is not paved, it should be located on a high,

well-drained site. Sometimes the closed shed willhave an elevated wood-decked tramway andwood floor if it is built over low ground. In thatcase, good ventilation of the space under the flooris essential.

Large, closed, unheated sheds with overheadbridge cranes (figs. 26, 27) are not flooredexcept where surface equipment operates to loadrailroad cars and trucks. The pile foundations inunpaved sheds should be so designed and con-structed that air can circulate freely under thebottom packages.

At some sawmills, lumberyards, and wood-working factories, lumber is moved in and outof racks or bins in the unheated, closed sheds.Aisles or driveways are provided for transport-ing the lumber to and from the bins, so’ that it

can be solid piled in the bins without difficulty.Some items at sawmills and wholesale and retailyards are placed on end in stalls (fig. 28).Paving the floor of these stalls assures dry ends.

Closed, unheated sheds beside railroad sidingsoften have an elevated floor to facilitate lumberhandling in and out of boxcars. The crawl spaceunder the elevated floor needs to be wellventilated.

Closed, Heated Sheds

If the air in a shed is heated, EMC conditionsare lowered. Moisture regain by stored drylumber can thereby be prevented (chapter 2).

Closed lumber sheds can be heated to lowerthe wood EMC by steam-heating coils, radiators,

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or unit heaters. Gas-fired unit heaters are some-times installed. lt is essential that some air cir-culation be created by strategically located fans.The heat supply can be controlled manually orautomatically. Manual control requires frequentobservations of outdoor and indoor wet- anddry-bulb temperatures so that the relative hu-midity in the shed can be estimated and valvesettings adjusted accordingly.

Temperature control in closed, heated shedsis often by a simple thermostat which regulateseither the heater or the heater fan. With chang-ing outdoor temperature and relative humidity,the thermostat in the storage area needs to befrequently reset to maintain the desired woodEMC.

Differential thermostats require less adjust-ment than simple thermostats in controllingshed heating. They automatically maintain shedtemperature a fixed number of degrees higherthan the outdoors temperature. Differentialthermostats will maintain an approximate EMClevel without periodic readjustments. They areinexpensive, and are available from a number ofnational suppliers.

Humidistats will initiate heating when therelative humidity goes above the adjusted setpoint, and can control the EMC of lumber accu-rately enough to seldom need readjustment. Forexample, a 7 percent EMC can be maintained ina closed storage shed over a wide temperaturerange if the relative humidity is kept at about35 percent.

Kiln-dried lumber is often stored in coolingsheds pending removal for factory processing orshipment. Cooling sheds may be either opensheds or closed, unheated sheds (fig. 29). Exces-sive moisture regain can occur when open coolingsheds are used for temporary lumber storage.However, open cooling sheds can be convertedto closed sheds; if this is done, humidistat con-trol of heated, circulated air is often desirable.Such humidistat control will maintain low mois-ture levels indefinitely in kiln-dry lumber.

Closed, heated sheds are seldom insulatedbecause generally they are heated only 10 or 15degrees above the temperature of the outside air.Such a temperature elevation will usually protecteven kiln-dry lumber from moisture regain.

If closed, heated sheds are used for air drying,the shed should not be so tight that all airexchange with the outside is prevented. In thatevent, humidity from the drying lumber would

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elevate the EMC and defeat the purposes of theheating.

Storing plywoodPlywood in storage must be protected from

changes in moisture content. A closed, unheatedshed is fully satisfactory for storing plywoodexcept for certain times of the year in humidareas such as the Gulf Coast, where storage in aclosed and heated shed would be better. Plywoodmust not be stored outside except for very shortperiods unless fully protected by a good pile roofor by complete coverage with a waterproofwrapper.

Plywood’s moisture content is normally below20 percent, so the material is usually stored insolid packages. Occasionally, however, some ply-wood may be received that has a moisture con-tent of 20 percent or more. Such material mustbe stickered sheet by sheet.

Plywood, especially the thinner sheets, has atendency to sag between supports. If the storageperiod is quite long, this sag may develop intopermanent deformation. Therefore, plywoodsheets should be stored on a platform foundation

When solid piling all thicknesses of plywood, inches on center for plywood to be open piled.the spacing of the cross supports must not ex- If the plywood is ½-inch thick or thicker, ateed 2 feet on centers. Stickered packages of sticker spacing of 2 feet is permissible. Allplywood may require closer spacing of cross stickers must be vertically alined so that thesupports, depending on the plywood sheet thick- weight of the plywood will be transmittedness. If the wet plywood is less than ½-inch directly to the foundation supports. This spacingthick, the maximum spacing of stickers is 18 prevents deformation of the sheets.

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CHAPTER 5: TREATING STORED LUMBER 2

Fungal infection and insect attack both poseserious hazards to stored lumber. Fungal infec-tion was found to be the principal cause of de-grade in a study of grade loss in l-inch southernpine lumber. Insect infestation also causes seri-ous losses in stored lumber, particularly in thewarmer parts of the U.S.

For protection from fungi and insects, lumbermay require a dip or spray treatment in achemical solution at the storage installation. Insome cases this treatment will supplement anearlier dip or spray at the sawmill.

To minimize fungal and insect attacks onstored lumber, air-drying yards should be keptsanitary and as open as possible to air circula-tion. Recommended practice includes locatingyards and sheds on well-drained ground. Removedebris, which is a source of infection, andweeds, which reduce air circulation. Pilingmethods should permit rapid drying of the lum-ber and also protect against wetting.

Open sheds should be well maintained with anample roof overhang to prevent wetting fromrain. In areas where termites or water-conduct-ing fungi may be troublesome, stock to be heldfor long periods should be set on foundationshigh enough to be inspected from beneath.

When Is Chemical TreatmentNeeded?

Prompt drying will often protect untreatedlumber from attack by stain, decay, and someinsects. For instance, untreated material uni-

2 Mention of chemical treatment in this chapter doesnot constitute a specific recommendation. Only thosechemicals registered by the U.S. Environmental Protec-tion Agency may be recommended, and then only foruses prescribed in the registration, and in the mannerand at the concentration prescrbed. The list of regis-tered chemicals varies from time to time. Prospectiveusers, therefore, should get current information onregistration status from the Environmental ProtectionAgency, Washingon, D.C.

formly below 20 percent moisture content isimmune from attack by fungi. With protectivestorage it will keep that immunity. However,dried lumber which regains moisture to alevel of more than 20 percent again becomessusceptible to stain and decay.

The sapwood of all wood species is more sus-ceptible than heartwood to decay, stain, orinsects. Therefore, the hazards are highest forwoods which usually contain a high percentageof sapwood. The heartwood of such species asredwood, the cedars, and some white oaks hashigh natural resistance to fungi and most in-sects. But few products-even from thesewoods-are of heartwood only.

Damp weather can increase the damage fromstain and decay fungi. Rainfall and humid con-ditions increase the hazard to unprotected woodin both open and solid piles.

Air temperature is highly important: Thestain and decay fungi grow most rapidly at 700to 90° F (210 to 32° C), no more than one-fifthas rapidly at 50° to 60° F (10° to 16° C), andcease growth at about 32° F (O 0 C). As a result,wood at about 25 to 30 percent moisture content,stored in solid piles in warm weather, may showevidences of stain within a week and early decayinfection within a month. The initial infections,which are not visible, probably started shortlyafter the wood was sawed. With temperaturesof 50° to 60° F (10° to 16° C), similar deteriora-tion requires five or more times as long. At 32°F (0° C) or below, the lumber can remain insolid piles indefinitely without adverse effects.

High humidity favors subterranean termites,but does not affect drywood termites or powder-post beetles. The influence of temperature on in-sect activity, however, is pronounced. Insects areinactive at temperatures of 50° F ( 10° C) orbelow, but increase their activity rapidly as thetemperature rises about this level. Insects willapproximately double their activity with eachincrease of 10° above 50° F, reaching maximumactivity levels at about 80° F (27°C).

When and Where IsTreatment Applied?

Stain and decay in lumber are normally con-trolled at sawmills, collection points, and dryingyards by drying the wood as rapidly as possiblebelow 20 percent moisture content. Lumber tobe air-dried may be treated with fungicidalsolution by dip or spray before the drying periodbegins. Sometimes an insecticide is mixed intothe solution if insects are likely to be a problem.

The layer of wood chemically protected by adip or spray is only “skin deep,” and will notstop fungi or insects that have already enteredthe wood. This is why stock is dipped as soon aspossible after it is sawed. To illustrate howquickly the dipping must be accomplished, thesafe times are estimated as: 1 day with tem-peratures of 800 F or above; 2 days at 70° F:1 week at 60° F; and 1 month at 50° F. Longerdelays at these temperatures progressively lowerthe benefit from surface treatments.

Generally, dip or spray treatments immedi-ately after cutting are designed to protect greenstock only when it is drying. If treated greenlumber is not air-dried to below 20 percent mois-ture content, prolonged storage may requireredipping or respraying of the lumber.

Efficient management of a lumber storageyard can eliminate situations which encouragegrowth of stain or decay fungi in stored lumber.When lumber is brought to a yard, an estimateshould be made as to how long the storage periodwill be. The superintendent, using this estimate,will be able to prescribe recommended storagepractices, He should also consider the timeneeded to ship the lumber to destination points,for during this time protection is also needed.

Lumber properly dipped in an antistain solu-tion at the sawmill can be stored in solid pilesfor up to 1 month in warm weather if furtherdrying is not required. If longer bulk storage isanticipated, dip-treated stock should be redipped.Additional dipping can protect pines and hard-woods from stain and decay for 6 to 8 weeks inwarm weather and western softwoods other thanpines for 4 to 6 months.

If the lumber was not dipped at the sawmill,dipping at the storage yard may still protect itfrom fungi during bulk storage provided thestock is not already infected. Infection would not

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occur if daytime temperatures in the intervalbetween sawing and receipt at the yard did notexceed about 400 F (50 C). If temperatureswere higher, however, fungus infection mayhave already taken place, and solid piling shouldbe avoided. Instead, lumber maybe dipped in afungicidal solution and open-piled.

Because a number of factors affect safestorage time, all dipped bundles should be labeledwith the date on which they were treated. Repre-sentative ones should be opened from time totime to determine the condition of the stock.Any lumber that shows signs of being inade-quately protected should be designated for earlyuse, redipped, or stickered for air drying.

Applying Chemical TreatmentLumber to be dipped at the storage installation

will probably be in unit packages. Thus thedipping procedures explained here will be forunit packages. When lumber is dipped, theamount of solution absorbed will be about 4 to 8percent of the wood weight, depending on typeof wood and moisture content at the time oftreatment.

Treating Area and Equipment

Location of the treating plant affects the costsand efficiency of the treating operation. Readyaccess of the plant to packaging and storageareas—and to railroad spurs or shipping docks—will keep costs to a minimum and insure anefficient handling operation.

Equipment for treating lumber often includesan electric hoist that runs on a monorail attachedto the ridge of a long, open shed. The treatingvat can be installed in or above the ground butshould be located in the center of the shed. Thisleaves protected areas in both ends of the shedwhere untreated packages can be brought in orthe treated packages loaded out. Dead or elec-trically operated rollers are often used in bothends of the shed.

The vat should be sufficiently large to admitthe largest unit package to be dipped and shouldhold sufficient solution to treat a number ofpackages without replenishment. Provision alsoshould be made for easily adding and removingthe treating solution. A well-designed vat would

be about 1½ times the height and width of thelargest package to be dipped and about 3 feetlonger. A drainboard wide enough to accommo-date several packages should be provided at theremoval side of the vat to free the hoist forcontinuous treating.

Some type of hold-down device, such as weightsor a heavy iron cradle, is required to keep thepackages submerged in the solution. Weightsshould be attached to the pallet that supports thepackages, not to the load in such a way as tocompress the packages against the vat bottom.In fact, the boards should be compressed againstone another as little as possible to allow thetreating solution to penetrate between them.

The vat should be supplied from a mixingtank of known capacity. This tank will carryextra treating solution which can be preparedwithout interrupting treating operations. Steamor electrical heating coils would be a desirablesupplement to the mixing tank to insure thatchemicals dissolve rapidly and completely.

Dipping Operation

Packages of lumber should be submerged inthe protective solution for at least 5 minutes,and for up to 15 minutes if long storage periodsare expected. Packages treated in a waterbornesolution should be turned on edge with the boardfaces parallel to the sides of the vat. This can bedone as the packages are placed in the vat. Pack-ages treated with an oil-borne solution need notbe turned entirely on edge during treatment.However, some means should be provided to tiltthe bundles as they are immersed to let airescape from the voids and to allow solution toflow in.

Packages removed from the treating solutionshould be drained for a sufficient time to recovermost runoff. A drainage period at least as longas the treating period usually will be adequate.

Treating for Insect Control

Insects can extensively damage stored lumberunder certain conditions. Treatment may beneeded to control such damage in both dry andgreen wood, regardless of the wetness or drynessof the storage location.

The principal insects that attack stored woodvary in their need for moisture. Ambrosia orpin-hole beetles invade green or partially dried

wood, but usually are only a minor hazard inlumber stored away from forested areas orsawmills.

Among the most troublesome insects are thosebelonging to the powder-post beetle group. Theseinsects chiefly attack partially dried sapwood andare particularly damaging to such large-poredhardwood species as oak, ash, hickory, walnut,and pecan.

The principal other insect that might attackstored lumber is the termite. There are twogeneral types—the subterranean and the dry-wood termite. Practically all woods are suscep-tible to their attack. Subterranean termites areby far the most prevalent type in the UnitedStates. They must have contact with some sourceof moisture, almost always the ground. Drywoodtermites occur only in limited areas along theGulf and Pacific Southwest coasts, particularlyin Florida and southern California. Drywoodtermites and powder-post beetles are the onlypests that primarily attack dry wood.

Properly applied treatments which are com-mercially available generally provide protectionto stored lumber against powder-post beetlesand termites.

It is important to realize that the dip treat-ments described here apply only to the protectionof the products in storage. Preservation of woodfor use requires different types of solutions andmethods of application.

For wood that might be treated only becauseof a subterranean termite hazard, a more efficientmethod of protecting the lumber would be totreat the ground under the storage piles or sheds.

Precautions With ChemicalsAll treating solutions should be so handled that

none, or as little as possible, gets on workers’skin and clothing. In particular, contact of theskin with the dry chemicals should be avoided.

When lumber dipped in water solutions is tobe painted, sufficient time must be allowedduring storage or before painting to allow thewood to dry adequately. Only rather short dryingperiods will be necessary to remove excessmoisture resulting from treatment with water-borne chemicals because the increase in moisturecontent from dipping or spraying will be small.Residual oil should be cleaned from any dryhardwood lumber to be painted.

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CHAPTER 6: AT SAWMILLS-LUMBER HANDLING AND STORAGE

Lumber storage varies from total outdoorexposure at small, portable sawmills to a highdegree of protection under roof at large, per-manent sawmills. Procedures will differ accord-ing to whether hardwood or softwood lumber isbeing sawn, and whether the sawmill uses acentral yard or does its own drying and planing.The mill’s degree of modernization will alsoaffect procedures.

Softwood SawmillsSmall Sawmills

Portable or semipermanent sawmills produc-ing softwood lumber are usually located near thesource of logs. The rough green lumber isusually assembled into a unit package for trans-port to an air-drying yard near the mill site, oris trucked to a central yarding location. Thesolid-piled unit packages of green lumber areexposed to the weather.

Green lumber at these small mills is seldomtreated with a fungicide, but often should be,because extended storage in the bulked handlingpackage increases the hazards of stain develop-ment (chapter 5). If the lumber is air dried atthe sawmill, the rough, dry lumber is trucked tothe buyer without protection. If the small sawmillowner also operates a planer, the finished lumbershould be tarpaulin-protected on the deliverytrucks, but is not so protected in most cases.

Green lumber is often trucked from smallsoftwood sawmills to a central yard. The lumberis sorted and stacked at this yard for either airdrying or kiln drying. A sorter is usually usedto segregate thicknesses, widths, lengths, andsometimes grades. The sorted lumber is usuallybuilt into solid packages and moved by lift truckto the stacker station. There, the solid packagesare made into stickered packages for drying.These stickered packages maybe placed on pilesin the air-drying yard, or may be stacked on kilntrucks for drying in track-type dry kilns. Thestickered packages may also be placed in apackage-loaded kiln for drying.

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Portable softwood sawmills not deliveringtheir lumber to a concentration yard either sellgreen lumber or air dry the sawed lumber at themill location. Mill-run lumber to be air dried istrucked to a yard site where hand-built air-drying piles are erected. The lumber may be flatpiled, crib piled, or end piled.

Large SawmillsAt large softwood sawmills, lumber moves

through two separate sequences of procedures,or “processing flows”. First, fresh-cut lumbermoves in a series of steps from the saw toeither dry kilns or an air-drying yard. Then thecompletely dried lumber moves through anotherprocessing flow to be finished, regraded, pack-aged, strapped, and stored for shipment asremanufactured lumber.

Lumber sawn at the larger softwood sawmillsis immediately sorted. The lumber is usuallystacked mechanically for kiln drying soon aftersorting. The kiln truckloads or stickered unitpackages often stand outdoors awaiting kilnspace or the accumulation of a kiln charge.Degrade from exposure in the upper courses ofsuch packages or kiln truckloads has justifiedthe construction of open sheds at many softwoodsawmills. After kiln drying, rough softwoodlumber is usually stored in open cooling shedsbefore processing in the planer mills.

Dry, rough lumber to be held for some time isstored in sheds. Lumber to be processed andshipped is taken to the planer mill, usually bylift truck or carrier. Dry, finished lumber is heldin a closed shed.

At large softwood sawmills, green lumber istransported from sorter to stacker by transferchains or transfer-track-type dump buggies.Conventional green chains may be roofed, butthe pulled lumber is often exposed to theweather. Edge, drop, and tray sorters are notusually roofed. Rough, dry lumber is movedfrom a dry sorting chain to storage in closedsheds by lift truck, carrier, or monorail.

In softwood operations which are large andmodernized, the rough kiln-dried lumber istransferred from the unstacker to the planer bytransfer chains. The finished and remanufacturedlumber is regraded, packaged, strapped, and isthen stored in closed, unheated storage sheds.

Kiln-dry rough lumber is usually kept underroof. However, outdoor areas between the planermill and finished lumber sheds are sometimesused for storing finished lumber as wrappedcarrier packages (fig. 31).

Some of the larger softwood sawmills enclosethe sorting equipment and store stickered kiln-truckloads of lumber under cover at the loadingend of the battery of dry kilns. Kiln-dry roughlumber is sometimes left on sticks and stored inan open shed until needed in the planer mill.Most often, however, the rough, dry lumber isregraded, packaged, and stored in a closed“rough dry shed,”

At the larger softwood sawmills, however, thetrend is toward a reduction in dry, rough lum-ber inventory with an increasing inventory offinished planer-mill products. The rough dryshed is being eliminated. The finished lumber ispackaged and strapped to stabilize the package,and stored in large closed sheds equipped withbridge cranes. The loading dock for both rail-road car and trailer truck loading is part ofthese closed sheds.

Hardwood SawmillsSawmills cutting hardwood lumber are usually

permanently located and set up. Green lumber athardwood sawmills, large and small, is almost

always handled and stored outdoors. The saw-mill and green chain may be under roof, but thebulk-piled sorted lumber is exposed without pro-tection until transferred either to the air-dryingyard, with’ or without a pile roof, or to the drykiln.

Small SawmillsAt small hardwood sawmills, the sawed lum-

ber is often sorted into three or four segrega-tions at the back end of the mill. This sortedlumber is then stacked into unit-handling pack-ages in stalls which are sometimes providedwith sticker guides. The unit packages aretransported from the stacking location to theair-drying yard by forklift truck and placed onthe pile foundations (fig. 32).

A forklift truck transports the stickered, air-dried packages to a station where inspection forgrade and tally is carried on while unstacking.Air-dried rough hardwood lumber often awaitsshipment outdoors in solid piles or packageswithout protection. The air-dried lumber isusually shipped from the sawmill by truck with-out protection

The small hardwood sawmill seldom has indoorstorage facilities for air-dried lumber. A smallremanufacturing plant to trim and rip air-driedhardwood lumber may be located in an open shed,but lumber storage space is usually quite limited.

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Large Sawmills

At larger hardwood sawmills, the lumber issorted into various classifications on a greenchain (fig. 33). Some lumber items may bestickered in stalls with sticker guides set u palongside the green chain. The packages are builtup on kiln trucks and tracks so that the com-pleted package can be rolled out for forklifttruck pickup and transport to the air-dryingyard. When hardwood lumber is to be stacked onkiln trucks for kiln drying or air drying (fig.34), a forklift moves solid-piled packages fromthe green chain to the stacker.

At sawmills where the hardwood lumber isstacked in hand-built piles for air drying, thelumber is solid-piled on dollies or carts at thegreen chain and pulled by tractor to the pilelocation. At a hardwood mill with dock-typeair-drying yards, the bulk-piled sorted lumber oncarts or wagons is tractor-drawn on the elevatedtram to the pile location. All too often, moreconcern for protective storage would reducedegrade in the yarded lumber.

Large hardwood sawmills may have a closedshed for storing air-dried rough lumber. Lumbernot meeting the requirements of a shipment isaccumulated there until ordered. Hardwood saw-mills with dry-kilns will have sheds for coolingand storing kiln-dried rough lumber awaitingshipment. Kiln-dried hardwood lumber is notordinarily stored for inventory purposes athardwood sawmills unless a factory, such as aflooring plant, is operated in connection with the

sawmill. Kiln-dried rough hardwood lumber isusually kept under cover until loaded into tightboxcars.

RecommendationsSoftwoods

Green lumber. —Treat green lumber with afungicide if bulk storage is extended, particularlyduring the warmer months (chapter 5). Specieslike the white pines must be stacked for dryingsoon after sawing to avoid brown stain.

Kiln-dried lumber. —Store dry lumber, bothrough and finished, under cover. Keep shedaccess doors closed during off-work periods.Inspect wrapped packages of finished lumberstored outdoors for wrapper ‘breaks and tears.Redry wetted lumber.

Hardwoods

Green lumber. —Stack for air drying or kilndrying soon after sawing. Treatment with afungicide may be necessary during warmermonths to prevent sap stain (chapter 5).

Air-dried lumber. —Store under cover to pre-vent moisture regain. Covers on outside bulk-piled stock should effectively prevent rainwaterentry. Keep bulked piles off of the ground toallow ventilation. Air-dried lumber can be storedin closed sheds, either bulked or on sticks. Keepshed doors closed when possible.

Kiln-dried lumber. –Store as bulked lumber inclosed, heated sheds.

CHAPTER 7: IN TRANSIT-LUMBER HANDLING AND STORAGE

If carelessly shipped, dry lumber can regainenough moisture to require redrying, and greenlumber can stain or decay. Such waste is totallyunnecessary. With proper transport procedures,even kiln-dried lumber can cross the UnitedStates—or be shipped to foreign ports—withoutany appreciable loss of quality.

Nationwide, a vast inventory of lumber is intransit at any one time by railroad, truck, orship. Lumber moves from sawmills to locationsof end use either directly or through wholesaleand retail lumberyards. Softwoods are usuallyshipped as finished lumber. Hardwoods moreoften move from the sawmill to the woodwork-ing plant as rough lumber, although kiln dryingand surfacing in transit may sometimes beinvolved. Coastal sawmills ship lumber by ocean-going vessels to domestic and foreign ports.

Present-day lumber shipments are usuallyunitized for mechanical handling. The strappedunit-handling packages are loaded by forkliftinto wide-door railroad boxcars, onto flatcars,and onto trucks. Ocean-going vessels are loadedby ship gear.

On the eastern seaboard of the United States,lumber from the Pacific Coast is readily avail-able because of low-cost sea transport via thePanama Canal. Often green lumber is shippedby sea because weight is not a major expense inthis type of shipping. On the other hand, lumbercrossing the United States by rail is usually kilndried because rail rates are based on weight.Railroads place southern and northeastern sup-pliers in a favorable shipping cost position forEastern markets.

Generally, when l-inch dry softwood lumberis shipped in tightly closed boxcars (fig. 35), inenclosed trucks, or in packages with completeand intact wrappers, average moisture contentchanges can generally be held to 0.2 percent permonth or less. In holds of ships, dry materialusually absorbs about 1.5 percent moistureduring normal shipping periods. If green materialis included in the cargo, the moisture regain of

the dry lumber may be doubled. (On deck, themoisture regain may be as much as 7 percent.However, dried lumber is seldom stowed ondeck.)

Truck TransportChanging transportation costs have led to

increased use of trucks for transport of lumberand wood-based products. Trucks have become amajor means of lumber transport for regionalremanufacture plants, for retail supply fromdistribution yards, and for hauls where the dis-tance from primary manufacture to customer iswithin about 1,500 miles.

Considerable quantities of air-dried lumber areshipped by truck from sawmills to factories orcustom kiln-drying plants. Tractor-trailer unitsare usually used for this purpose, and in mostinstances the trailer is a flatbed unit that can beloaded and unloaded by lift truck. The lumber isanchored to the trailer by chains tightened withload binders.

Few data are available on moisture changesduring truck shipment. Time in transit is short,

seldom exceeding a week even on longer hauls,so little change in lumber’s moisture contentwould be expected from atmospheric humidity.However, trucked lumber can be wet by rain orsplashed-up road water.

High value, air-dried lumber is often protectedby covering the load with canvas tarpaulins (fig.36). Lower grade lumber is seldom protected atall, especially on short hauls. Some protection isrecommended during truck transport within awet or moist climate zone during wet periods.Precautions should also be taken when a ship-ment is going to cross several climate or elevationzones.

Rail TransportSome years ago both the U.S. Forest Products

Laboratory and the Canadian Western ForestProducts Laboratory studied the changes inmoisture content of softwood lumber shipped intight railroad boxcars from West Coast saw-mills to Midwestern United States and EasternCanadian markets.

The U.S. Forest Products Laboratory studiesinvolved five boxcar loads of l-inch clearDouglas-fir shipped from a West Coast sawmillto the Chicago, Ill., area during late winter andspring months. The time in rail transit averaged18.5 days, the shortest period being 14 days andthe longest 22 days. Table 4 shows the averagemoisture content at the time of loading and thechange while in transit.

Average moisture content of the five carloadsof kiln-dry boards at the time of loading was 8percent, and the average gain in moisture con-tent was 0.2 percent. These values are based onan average of 18 test boards distributed through-out the boxcar load in each shipment. The test

boards were checked for moisture content by theovendry method both before loading and whenunloaded. Moisture content changes in the testboards did not correlate with their position inthe boxcar.

In a different study, test boards in a carloadof Douglas-fir quarter-round and crown molding,which were at 8 percent moisture content whenloaded, regained 0.8 percent in moisture in a20-day transit period from the West Coast tothe vicinity of Chicago. Thus, no significantchange in moisture content of dry lumber needbe expected during the usual haul in tightboxcars.

Table 4. —Gain in lumber moisture content duringU.S. rail shipment

The rail shipments studied by the CanadianWestern Forest Products Laboratory involved19 boxcar loads of softwood lumber with anaverage transit time from Vancouver to Mont-real or Ottawa of 20 days. The shortest transitperiod was 12 days and the longest 25 days.Shipments were made during each season of theyear. The test boards for each shipment, 18to 33 in number, were distributed uniformlythroughout the lumber in each boxcar. Thechanges in moisture content during these railshipments of kiln-dried lumber are presented intable 5. It was concluded that kiln-dried lumberwill arrive at its destination in eastern Canadain satisfactory condition.

A study of moisture changes in rail shipmentsof kiln-dried hardwood lumber was conductedby the U.S. Forest Products Laboratory. Theseshipments were of kiln-dried pecan lumber,transported in wide-door boxcars (fig. 37) from

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midsouth Mississippi to a furniture company inNorth Carolina, a distance of about 900 miles.Each load of unitized lumber packages containedfour test boards for moisture analysis. Test ship-ments were made from June through November,with the results summarized in table 6.

Changes in moisture content were not con-sidered commercially significant, and the lumberwas moved into furniture production withoutadditional processing. Since these studies wereconducted, the furniture company has utilized

roller-bed boxcars for these shipments of kiln-dried pecan lumber (fig. 38).

Some shippers use “chain” flatcars for lumbershipments (fig. 39). These flatcars are loadedwith unit packages of bulked lumber by lifttruck. When the carload is in place, it is anchoredor bound to the car by chains thrown over theload and tightened with ratchet load binders.These chain cars may or may not have bulkheadsat the flatcar ends.

of moisture content, even on long hauls. Flatcarscan save handling time and shipping cost. Theload of lumber per flatcar may be twice that perconventional boxcar. Flatcars tend to offer lowerper-unit freight rates and can be loaded by lifttrucks to save handling time.

Unitized packages on flatcars are usually pro-tected, either partially by tarpaulins or entirelyby flexible, waterproof packaging which com-pletely “tailor-wraps” each package. One commontype of waterproof packaging uses compositekraft paper that is glassfiber-reinforced andpolymer-coated (fig. 40). The packaging is fre-quently supplied with additional reinforcementat stress points such as edges and corners.Improvements in packaging materials havemade possible the shipment of kiln-dry lumberwith little change in moisture content and agood retention of brightness by the boards.

Wrapping for unitized packages of lumbershould be free from rips to be effective. Rainwhich enters the rips is held by the sheeting andthe package may act as a humidifier. If so,moisture regain may be higher than if thelumber were unprotected (chapter 3).

Ship TransportLumber transported from the United States

by ship falls into one of two categories: (1)Pacific Coast softwood lumber, usually green,destined for the U.S. Eastern Seaboard States;(2) dried, finished lumber for foreign ports.Green lumber is often stored on deck, exposedto the weather; seasoned lumber is usuallystowed below decks in ship holds, either by itselfor together with green lumber.

A study conducted in Canada involved 33shipments of lumber from the Canadian westcoast to five different ports. The study concludedthat seasoned lumber stored below decks, eitherby itself or together with green lumber, will notundergo moisture regain of serious proportions.This study indicates that well-dried lumbermay undergo significant moisture regain ifstored on deck, although it is not commonly sostored.

Each test shipment consisted of one or morestrapped unit packages containing 48 end-coated,4-foot sample boards. Moisture content andweight of each board in the package were de-termined when the test packages were assembled.Douglas-fir and western hemlock were used in

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the tests. The test packages were stored in theships’ holds or below decks with commercialshipments of dry or green lumber. Test packagesof kiln-dried lumber were stowed on deck withgreen lumber in ocean shipments to South Africaand Montreal, Canada.

Upon arrival at the port of destination, theindividual boards making up the test packageswere weighed and their moisture content de-termined. The moisture gains for the variousshipments are presented in table 7.

Stowage of l-inch kiln-dried lumber togetherwith green lumber below decks resulted in almosttwice the overall gain in moisture content as

compared with dry lumber stowed alone. Buteven when green and dry were stored together,moisture regain in the dry lumber was notenough to seriously impair lumber quality.

Kiln-dried lumber stowed on deck, even thoughprotected from direct contact with the weather,regained almost four times more moisture thandid dry lumber stowed with other dry lumberbelow decks. However, on-deck storage ofdried lumber is not a common practice.

Similar tests were made with 2-inch insteadof l-inch Douglas-fir lumber. The 2-inchdried lumber had a moisture content of 9 to 10percent when stowed. Shipments were to the

same ports as with the l-inch lumber, except notto Trinidad. The overall average moisture gainsfor these shipments of 2-inch lumber were asfollows :

The average moisture content of this 2-inchlumber at the time the test packages were loadedwas slightly higher than the l-inch lumber, andthe moisture regain somewhat less. The moistureincrease for 2-inch kiln-dried lumber stowedwith green lumber below decks and on deck isabout the same as for the l-inch kiln-driedlumber.

The Canadian Laboratory concluded that whenwell-dried lumber was stowed below decks thelumber would arrive at its port of destination ata satisfactory moisture content. The data indi-cate the advantage of stowing dry lumberseparate from green lumber below decks.

No data are available on moisture contentchanges in present-day ocean shipments ofunitized dry lumber.

RecommendationsSoftwoods

1. Green lumber is unitized and shipped,sometimes without protection, by truck, railwayflatcar, or ocean-going vessels. Extended transittime may result in degrade from mold, stain,and decay fungi, especially during warmweather. Green lumber may need to be treatedwith a fungicide before shipping during thewarmer months (chapter 5).

2. Dry, finished lumber should be shipped intight boxcars, as wrapped unit packages onflatcars, or below decks in ships. Protection maynot be necessary during short truck hauls duringdry weather; otherwise, tarpaulin coverageshould be used.

Hardwoods

1. Green lumber shipments can be madewithout protection when the transit periods areshort. The lumber should be air dried prior tolong periods of rail, truck, and ship transport.

2. Air-dried lumber can generally be shippedby truck, rail, or ocean-going vessel withoutprotection.

3. Kiln-dried lumber requires protectionduring transit. Use tight boxcars or packagewrappers for rail shipments. Use watertighttarpaulins on open truck shipments. Stow belowdecks on vessels.

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CHAPTER 8: AT LUMBER DISTRIBUTING

YARDS-HANDLING AND STORAGE

Lumber distributing yards may be eitherwholesale or retail. Handling systems at theseyards will depend upon the volume of lumberbeing stored and the quantity moving in and outof the yard.

At the larger distributing yards, lift trucks,including side loaders and end loaders (fig. 4l),are used for unit-package handling. Incomingboxcar shipments of loose dry lumber are usuallyunitized when unloaded for yarding, The unitizedpackages are often stored outdoors briefly,without protection (fig. 42) ; extended storageis often in open or closed sheds (fig. 43). Lumberon incoming railroad chain cars, flatcars, andgondola cars is usually unitized for forklift truckor crane unloading. Shipments to the largerdistributing yards in open-top trucks are oftenstrapped packages that can be unloaded byforklift.

Straddle carriers (fig. 44) may be used in thelarger yards where haul distances justify the useof these more rapid transport vehicles. Largerdistribution yards are usually wholesale opera-tions which ship to woodworking plants, retaillumberyards, or construction sites. Their ship-ments are usually unitized. Shipping is by truck,both enclosed and open-bed.

At the smaller distributing yards, lumber isunloaded from boxcars onto trucks and movedto open or closed sheds where the lumber is piledin bins. Facilities for unit-package handling arenot often available. Shipments out of thesesmaller yards, usually retail operations, areoften on a job-lot basis. Thus the inventory ofany one lumber item is relatively small. Hauls toa building site are usually by open truck withoutprotection. If such shipments will be exposed

outdoors upon delivery, some sort of temporaryprotection, as a sheet wrapping, is recommended(chapter 10).

Outdoor StorageLumber is often stored outdoors if shed or

warehouse space is not available (fig. 45).Unprotected outdoor storage is satisfactory,although not ideal, for such lumber items astimbers and lumber to be used for less exactingrequirements. However, kiln-dried lumber shouldnot be stored outdoors unprotected. Such lumber,even if protected from rain by a cover, willdampen excessively for interior uses whenstored outdoors for long periods in most parts ofthe United States. If the storage period is to bebrief, piled packages of dry, solid-stacked lumberare often protected by canvas or plastic tar-paulins. Strapped packages of lumber wrappedwith waterproof paper are often stored outdoorswithout additional protection.

Outdoor storage may become an air-dryingprocess if incoming lumber in a green or onlypartially dried condition is stickered rather thanbulk piled. Whether lumber yarded outdoorsshould be bulk piled or stickered for further dry-ing depends upon the lumber’s moisture contentand intended use. Lumber at a moisture content of20 percent or more that is to be held for sometime, particularly in warm weather, should bestickered for additional air drying. Piles ofstickered packages should be roofed to keepmoisture regain during rainy weather to aminimum (chapter 4).

Solid-piled green lumber is likely to deteriorateif held for an extended time. Stain and mold willdevelop first, followed by decay. Dry lumber in

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solid packages, if not protected from wetting bywrappings or pile roofs, will take on excessivemoisture with extended storage.

Indoor StorageAll dry lumber items can be protected in the

three types of shed detailed in chapter 4: (1)open sheds, (2) closed, unheated sheds, and(3) closed, heated sheds.

Open Sheds

An open shed at a distribution yard providesa permanent roof over the stored lumber (fig.46). The atmospheric conditions within the openshed are the same as outdoors, and provideequilibrium conditions for air-dried lumber.Stickered packages can be stored in open shedsfor further air drying.

The shed may be open on all sides or on oneside only. The lumber is piled and unpiled fromthe open sides. At the larger distributing yards,forklift trucks are used to handle packages oflumber placed in rows of piles across the shed.Certain grades and sizes of lumber are oftenhand-stacked in bins setup in the bays (fig. 47).

Lumber kiln dried to moisture content levels of10 percent or less is not often stored in opensheds unless the storage period is expected to beshort.

Closed, Unheated ShedsClosed sheds are used primarily for the storage

of well-dried lumber items. The object of thistype of indoor storage is to prevent excessiveregain of moisture by the dry stock. The lumberis solid piled (fig. 48).

At the larger distributing yards, unit packagesare handled with forklift trucks. Blocks ofpackages of similar lumber items are built upfor ready accessibility. The shed is often paved.Patterned and specialty grades of lumber maybe hand-stacked in bins from a central aisle orroadway (fig. 49). Moldings of various sizes and,

patterns which have been bundled and wrappedat the producing mill are often stored upright atthe distributing yard (fig. 50).

Kiln-dried lumber stored in an unheated,closed shed will absorb some moisture becausethe wood’s average moisture content is usuallylower than the prevailing wood equilibriummoisture content ( EMC ) in the shed. The lum-ber tends to come to equilibrium with the higherEMC conditions, with the outer parts of the pilesgaining moisture the most rapidly (chapter 2).

The temperature inside of the closed, unheatedshed will be somewhat higher than outdoorsbecause of heat radiating from a roof warmed

by solar radiation. The increased shed tempera-ture will lower the average or effective EMCconditions to some extent.

Closed, Heated ShedsEMC conditions in a closed shed can be lowered

by heating the air being circulated in the build-ing. A closed shed can be heated with steam-heating coils, steam radiators, steam unit heaters,or gas-fired unit heaters. The heated air shouldbe circulated around the stored lumber continu-ously. Unit-heater operation is often thermosta-tically controlled by on-and-off operation of theunit-heater fan. But a better procedure is toattain full-time fan operation by using an auto-matic valve on the steam or gas line. This valveis controlled by the thermostat or humidistat.Then, with changing outdor temperature andrelative humidity the indoor shed temperature isautomatically set to maintain the desired EMCcondition.

RecommendationsSoftwoods

1. Green lumber can be stored outdoors with-out protection in cool weather, provided that thestorage periods are not extended. In warmweather, the risk of fungal stain, decay, or insectinfestation makes prompt snickering, and per-haps chemical treatment, advisable before stor-age (chapter 5).

2. Dry lumber requires protection fromweathering and moisture regain. Wrapped pack-ages stored outdoors need to be inspected for

wrapper deterioration; torn wrappers should berepaired or the package quickly moved underroof. Open or closed shed storage offers the bestprotection.

Hardwoods

1. Green or partially dried rough lumbershould be stickered and stacked for air drying.High value lumber should be air dried in an openshed.

2. Air-dried lumber when bulked requiresprotection from weathering and moisture re-gain. Outdoor storage requires suitable raintightcover and some elevation off the ground. Storagein open sheds is ideal.

3. Kiln-dried lumber should be bulk piled andstored in a closed shed. Heated storage isadvantageous.

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CHAPTER 9: AT WOODWORKING FACTORIES—

LUMBER HANDLING AND STORAGE

Woodworking factories buy lumber eitherdirectly from sawmills or from wholesale dis-tributing yards. Green, partially air-dried, air-dried, and kiln-dried lumber-all is delivered tosuch plants. The storage conditions at the plantare adjusted to further dry the lumber if neces-sary, or to prevent moisture changes. Lumber isstored both outdoors and in sheds. In manyinstances, the lumber is kiln dried at the factory.If so, cooling sheds and indoor storage rooms areoften used to store the lumber before use.

Storage FacilitiesGreen lumber often arrives at a woodworking

factory as solid packages (fig. 51) which arethen stickered for drying. Slower drying hard-woods like oak are built into unit packages fordrying in a conventional air-drying yard or inspecially built open sheds (fig. 52). However,some woodworking plants air dry hardwoodssuch as oak on kiln trucks prior to kiln drying(fig. 53). The faster drying hardwoods areusually stickered for kiln drying while green,although the thicker sizes may require air dryingfirst. Green softwoods are stickered for immedi-ate kiln drying.

Some woodworking factories do not have drykiln equipment, but employ the facilities of cus-tom kiln-drying operations. Lumber shipmentsare kiln dried and often surfaced at the customkiln-drying plant while enroute from the sawmillto the factory.

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Air-drying yards at woodworking factoriesshould be located at sites favoring good drying.Such yards should be laid out to facilitate lumberhandling. The alleys or roadways are often pavedand the pile foundations permanent, particular yin line-type yards. Pile covers should be used.Yarding is usually done with forklift trucksbecause most woodworking factories have con-verted their air-drying yards from hand-builtpiles to unit-package handling.

Partially air-dried lumber, either softwood orhardwood, is usually stickered for kiln drying.Stickered unit packages are sometimes storedoutdoors without protective cover before loadinginto a package-loaded dry kiln, or are placed onkiln trucks for drying in a track-type dry kiln.Kiln-truckloads of green, paretically air-dried, orwell air-dried lumber are sometimes stored in a“green” end storage shed of a dry-kiln installationbefore loading into the dry kiln. Such storageunder roof protects high value lumber.

If kiln-dried lumber must be stored outdoors,it should be bulk piled well off the ground onsupporting foundations. Sheet plastic covers onthese piles will cut down moisture regain. If thestorage period is extended, redrying may benecessary, requiring that the lumber be stickered.

Unit packages of softwood lumber, kiln driedand wrapped, are often stored outdoors at mill-work factories (fig. 54). The storage period isusually brief. In extended outdoor storage, thewrappers on kiln-dried packages of lumbershould be periodically inspected and repaired(chapter 4). Extended exposure of unit packageswith damaged wrappers can increase losses dueto stain and decay.

Open ShedsLumber stored in an open shed is protected

from weathering. The shed roof shields thelumber from exposure to direct sunshine andrain. Green and partially air-dried lumber canbe stickered, placed in the open shed, and dried.Well air-dried lumber can be bulk piled andstored in an open shed. The range of moisturecontent in the package may be reduced withduration of storage if at the time of bulk pilingthe range was fairly high.

Kiln-dried lumber is sometimes stored in opensheds at woodworking plants with the realiza-tion that moisture regain will take place. Thestorage period must be reasonably short if re-drying is not planned. Waterproof paper wrap-

ping will retard moisture regain during short-term storage of kiln-dried lumber in open sheds.

At many woodworking factories, cooling shedsto relieve stresses in lumber after kiln dryingare essentially open sheds. Stickered kiln-chargesof lumber should not be left long in suchsheds, or moisture regain may become so greatthat the lumber cannot meet manufacturers’requirements.

Closed, Unheated ShedsThe open shed provides protection from sun

and rain, but the closed shed, in addition, pro-tects the lumber from winds. Thus, the closed,unheated shed is not suited to air drying. Wellair-dried stock is bulk piled for storage in thesesheds. The range in moisture content will bereduced with extended storage. Kiln-dried lum-ber is stored in closed, unheated sheds with theexpectation that some moisture regain will takeplace, but less rapidly than in an open shed.Reduced air circulation and some heating of theshed by solar radiation help to keep the lumber’smoisture regain low.

Many dry-kiln cooling sheds at woodworkingfactories (fig. 55) can be classified as closed,unheated storage sheds. The access doors, how-ever, must be kept closed most of the time orthey are essentially open sheds. Warming byboth solar radiation and heat from the dry kilnscan reduce the wood EMC conditions in thecooling shed. Stickered lumber can be storedthere for some time without excessive moistureregain.

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Kiln-dried lumber in closed, unheated shedsrequires bulk piling during extended storage tokeep moisture regain limited. Redrying maybecome necessary to reduce the moisture gradientwithin and between boards of the lot when theduration of storage in the closed, unheated shedis greatly extended.

Closed, Heated Sheds

Cooling sheds for kiln-dried lumber at wood-working factories are sometimes heated duringcool, damp weather — generally during thewinter-to keep the lumber EMC low (fig. 56).However, heating of such sheds is seldomthermostatically controlled, and all heat is turnedoff during the summer months.

Some woodworking plants include heatedstorage rooms where lumber is held until neededin the rough mill. Heat in these rooms is oftenregulated by thermostat, but is turned off duringthe summer. Such rooms are not used for dryinglumber.

Handling EquipmentFactories using track-type dry kilns arrange

the plant layout so that the stickered kiln truck-loads of lumber can be transferred and movedinto the rough mill. Here the loads are usuallyplaced on a lumber lift. As the layers are re-moved by the cutoff sawyers, stickers are re-moved by hand and turned to the lumber-stacking area by conveyor. Stickers may also beplaced in staked dollies, trucks, or pallets fortransfer to the stackers.

At some factories, forklift trucks serve anair-drying or storage yard (fig. 57), servepackage-loaded dry kilns, or load kiln trucks fortrack-type kilns. At such factories the stickeredpackages are placed on a roller or chain con-veyor feeding a breakdown hoist. The lumberslides off onto a conveyor feeding the sawyersin a rough mill. The stickers are conveyed tothe stackers or into a bin pallet. A modificationof the system is to unstack the packages at anunstacker station and perhaps do some sorting.Then the bulked packages of dry lumber aremoved by conveyor or lift truck to the roughmill or the cutup department of the factory.

Recommendationssoftwoods

1. Green lumber must be stickered for dryingif deterioration due to stain and decay is to beavoided.

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2. Partially dry lumber can be bulked andstored in an open shed if its moisture content isless than 20 percent. If the moisture content isabove 20 percent, either sticker for additionaldrying or plan immediate use, particularly insummer months.

3. Kiln-dried lumber should be bulk piled andstored in a heated shed. Wrapping unit packageswith waterproof paper and storing outdoors issatisfactory for temporary storage. Repair tornwrappers.

Hardwoods

1. Green lumber must be stickered for drying.If the stickered units are air dried outdoors, pilecovers on high-value lumber are inexpensive.Storage of stickered lumber in an open shedgives better protection than with pile covers.

2. Air-dried lumber can be bulked and storedin an open shed. If the lumber exceeds 20 per-cent moisture content, snickering and furtherdrying in a conventional air-drying yard or inan open shed is beneficial.

3. Kiln-dried lumber should be stored in aheated cooling shed if the stock is left on stickspending transport to the rough mill or cutup

plant. If the stock is bulked for storage outdoors,protection from weather is essential and thestorage period must be limited. Bulked indoorstorage should be in an EMC-controlled storageshed.

CHAPTER 10: AT BUILDING SITES—LUMBER

HANDLING AND STORAGE

Lumber is not often protected from theweather at construction sites, although in manyinstances it should be. Lumber is commonlyplaced on the ground in open areas near thebuilding site as bulked and strapped packages(fig. 58). Supports under such packages areuseful to prevent wetting from mud and groundwater. At large construction locations, such asapartment buildings, office buildings, and con-dominiums, the strapped unit packages are de-livered to the area on roller bed trucks androlled off onto the ground (fig. 59). Sometimesthese packages are still wrapped with water-proof paper. However, protection is lost ifwrappers are torn.

Hazards From Moisture RegainPrefabricated building parts such as roof

trusses are sometimes dumped on the ground atthe building site and left lying unprotected (fig.60). In warm, rainy weather, moisture regaincan result in fungal staining. Wetting of thelumber also results in swelling. Subsequentshrinkage of the framing may contribute tostructural distortions. Extended storage of lum-ber over about 20 percent moisture contentwithout drying can allow decay to develop.

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So far as possible, deliveries of materialsshould be arranged to minimize onsite storagetime. Delivery of millwork, for instance, mightbe deferred until the partly completed buildingoffers a source of protection. Once the materialshave been delivered construction should proceedrapidly. As soon as the house is completed,exterior surfaces should be primed with paint.

When weather is bad, such as during winterin the northern sections of the country, someprotection is afforded by plastic sheeting (fig. 62).

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Recommendations lumber by roller bed trucks may result in the

The following recommendations, if followed,packages being dumped onto the ground. If theconstruction project is large enough to warrant

should help minimize lumber deterioration at thebuilding site:

use of a lift truck, have stringers laid on the

(1) Do not unload the lumber in the rain ifground to support the packages of lumber.

possible. Delivery by the distributor may need (3) Protect millwork from the weather and

to be delayed. from damage such as glass breakage.

(2) Try to avoid unloading lumber directly (4) Schedule deliveries to keep exposed-onto the ground. Delivery of unit packages of storage times as short as possible.

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ADDITIONAL INFORMATION

55

56

GLOSSARY

58

59

60

61

INDEX

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