Hard Materials

Topic 2217

By Kathryn Wagar

Hard Materials

• Working with outdoor lumber

• Building Tips

• Designing and Building Stairs

Working with outdoor lumber

• What you should know

• How Pressure-treatments work

• Types of Outdoor lumber

• Pentachlorophenol-treated lumber

• Chromated Copper Arsenate-treated lumber

Things you should know about pressure treated lumber

• In any outdoor project the wood suffers from constant exposure to the elements

• To prolong the life of the project, you will want to use types of wood that weather well– Unprocessed woods: Redwood, cedar, cypress– Pressure-treated lumber or “outdoor” lumber

What you should know Cont.

• Natural decay-resistant woods have become quite expensive– A sunshade gazebo made from redwood will

cost you two to four times what it would cost to build the same project from ordinary spruce and fir.

Inexpensive Alternative

• Outdoor Lumber– This is ordinary spruce and fir lumber that has

been “cooked” at high pressures in chemical preservatives so that the chemicals penetrate deep into the wood

– This treatment makes the lumber every bit as decay-resistant as the natural alternatives

Cons to using “Outdoor” Lumber

• It also makes the lumber potentially harmful, if not handled correctly– The chemicals used to treat outdoor lumber can

be poisonous to plants, pets, and people– If you’re going to work with outdoor lumber, it

behooves you to know something about it, and its dangers, so that you can avoid any problems.

How Pressure-Treatments Work

• Why Wood deteriorates

• Why Chemicals are used

• Importance of technique

Why Wood Deteriorates

• Two reasons: – Fungal decay or insect attack– Requires that certain conditions exist before it can

proceed– Both fungus and insects require sufficient oxygen,

moisture, and food to do their work– The wood itself serves as the food, oxygen is

always present in the air surrounding the wood, and the outdoors gets awfully wet from time to time

Why Chemicals are Used

• The chemicals used to treat outdoor lumber prevent fungal decay and insect damage by poisoning the food source– As a result, treated lumber can maintain its

integrity for many years– Estimates of the life of pressure-treated wood

range from 40 up to 100 years, depending on the chemical, the wood type, and how the wood is used.

Importance of Poisoning Technique

• When you poison a board, it’s important to poison the entire board, inside and out.– This is why the lumber is pressure-treated– You can paint, stain, or even soak ordinary

lumber in the same chemicals, but not get the same results

– The protection will only extend a short distance into the surface of the wood

Importance of Poisoning Technique

– Prior to the widespread availability of pressure-treated lumber, some companies would “incise” the lumber before treating it, in an attempt to make the wood more decay-resistant.

• They ran the stock between sharp toothed rollers to separate the wood fibers and allow the preservative to penetrate more deeply

• But these incisions still did not allow the preservative to soak in much beyond the depth of the cuts.

Commercial Pressure-Treating

• Distributes the preservative throughout the wood– Treating mills typically dry the wood to about

20% moisture content, then stack the lumber in a huge ‘retort’.

– After sealing the retort, they pump all the air out, creating a vacuum and extracting most of the remaining moisture

Commercial Pressure Treating Cont.

• Once the moisture falls to the desired level, the retort is flooded with preservative and pressurized to at least 175 pounds per inch– This pressure is kept up for hours, drying the

preservative into every wood cell

Commercial Pressure Treating Cont.

– After a prescribed time, the retort is drained and all the air pumped out, creating a second vacuum to remove any excess preservative or moisture

– The wood is removed from the retort and stacked in the open air to complete the drying process

Any Questions?

Types of Outdoor Lumber

• There are three types of pressure-treated lumber widely available today, and these are classified according to the chemicals they have been treated with:– Creosote– Pentachlorophenol– Chromated Copper Arsenate (CCA) (Most

common)

Creosote-treated Lumber

• Oldest of wood preservations

• Oily or dry

• Harmful to pets and humans

• Minimizing dangers

Creosote

• A coal tar distillate

• Oldest of the wood preservations used today– Most commonly used in utility poles, railroad

tiles, and landscape timbers– Applied under pressure with considerable heat

to make the solution thin enough to fully penetrate the wood

Creosote

• Lumber can be oily or dry, depending on the degree of treatment, and if they all emit a strong odor– Paint will not bond to creosote surfaces– Creosote doesn’t fix chemically to wood– Preservation will “Leech” out

Leeching of Creosote

• Occurs in warm weather– Makes the wood harmful to plants – Newly creosoted timbers should not be used for

gardens– Old railroad tiles that have lost most of the

preservation may be used– Once preservation leeches out, wood may

decay

Creosote can be harmful to Pets and People

• Sticky residue that accumulates on your hands and arms as you work with the treated lumber can cause skin irritation

• The fumes are poisonous

Dangers that can be minimized

• Dangers can be minimized by sealing the wood with urethane, epoxy, or shellac– helps prevent leeching– Adds or work and money– Don’t use where it will come in contact with

pets and humans

Examples

• Good uses for Creosote lumber– piers– bridges– poles– ties, – landscape timbers

Questions?

Pentachlorophenol-treated lumber

• Definition: EPA-registered pesticide containing chemical Pentachlorophenol applied to lumber

– commonly called “penta”

Penta Lumber

• Can be either water or oil soluble– both are toxic– Neither bond permanently to wood– Has similar problems as creosoted lumber– Only advantage over creosote is that it’s not as

messy to work with and it can be painted on after being set out in weather for some time

Penta Lumber

• Dangerous to use in areas that it may come in contact with people (particularly bare skin), animals, and food do to toxicity and leeching problems

• Best suited for remote structures where it will pose no serious threat

• Today’s utility poles are generally treated with penta

Questions?

Chromated Copper Arsenate-Treated Lumber

• Facts

• Dangers/advantages

• Uses for Different strengths

• uses

Facts of CCA

• Newest development in pressure-treated lumber– This is another EPA-registered pesticide,

containing inorganic arsenic– Water soluble– No fumes, can be used in interiors– Bonds permanently with wood– Can be painted– Best choice for homeowner outdoor projects

Dangers/Advantages

• Even though CCA itself is toxic, when it’s bonded to wood, it’s relatively harmless– Little residue do to not leeching

– Still recommended to let it weather before children and pets go near structures

– Once structure is “washed” it’s relatively harmless

– Should never be used in areas that it may come in contact with food and water

Uses for Different Strengths

• Treatment plants use CCA solutions of different strengths, depending on the intended use of the lumber– most common strength is .40 lb/ft3 of wood after

pressure treating (referred to as the retention figure)

– This provides an acceptable balance between the expected life of the wood and the cost of the chemical treatment

Uses

• Fence posts, small structural timbers (4X4’s), landscape timbers -- wood that will come in direct contact with the ground -- is generally rated at .40 pounds– most building supply stores will only carry .40

pounds– Decking and timbers that don’t touch the ground

may not need that high of rating

Uses

• If you get lower rated stock, you can save some money– If you’re using larger timbers than 4 X 4’s as

structural members, you may need to put out the extra expense for a higher rating

– Consult the notes to be sure of exactly what you need

Retention Level General Use Specific Uses

.25 Above GroundUses

Decking boardsFence boards, Plates, Railings, JoistsSills, headers, furring strips, Seating planks

.40 Soil or freshwater contact(structural)

Posts, small timbers (4X4’s),Landscape timbers, Retaining walls,boardwalks, Grape stakes, and greenhouses

.60 Soil or freshwater contact(structural)

Foundations (wood), building poles,decking/framing lumber, dock planks subjectto salt water splash, and bridge timbers

.80 Piles – Soil orfresh watercontact(strucutral)

Piles, foundaiton piles, entirely buried

2.5 Salt WaterContact

Piling, timbers, framing lumber, bulkheads,and retaining walls

Big Advantages• One of the big advantages of CCA-treated lumber

is that it can be painted– Air-dry for two to six months before you paint unless

it is kiln-dried (unusual)• Helps to make sure all water has evaporated and the paint

will bond properly

Big Advantages

– Additional note:• When CCA first appeared, the chemical solutions

contained impurities such as sulfate and sodium

• These are called “salt” solutions, and they would precipitate out of the wood to form a whitish or greenish-gray residue on the surface

• This residue contained high levels of arsenic and would quickly corrode nails and fasteners

Big Advantages

• Today, most manufacturers use a different type of CCA solution, called an “oxide” solution– This produces clean, dry, well-preserved

lumber, relatively fee of any arsenic-tainted residue

– You should not have any problem with lumber treated with this type of CCA

Other Warnings

• Even though pressure-treated lumber is relatively safe if used properly, it does contain potentially dangerous chemicals– Because of this, you should handle outdoor

lumber with respect and take certain precautions when working with it

– Probably the most important precaution is to never burn the scraps in the open, in a fireplace, or in a stove

Other Warnings Cont.

• All types of outdoor lumber -- creosote, penta, and CCA -- produce poisonous gases when burned

• When you’re done working, carefully clean up all the scraps and sawdust

• Dispose of these in a local landfill, or bury them yourself

Any Questions?

Building Tips

• Buying wood

• buying hardware

• Prevention maintenance

Purchasing Wood

• When purchasing pressure-treated lumber, pay attention to what species of wood you’re buying

Purchasing Wood

• East of the Mississippi, the predominant wood varieties used are Southern Yellow Pine, a good hard conifer wood; and Red Pine Used mostly for fence posts and landscape timbers

• West of the Mississippi, Ponderosa Pine predominates

Purchasing Wood

– All three of the listed species are well suited fore pressure-treating, and they have good structural integrity and dimensional stability

– Douglas Fir, Spruce, and White Pine, along with most common hardwoods, do not accept chemical preservations well

– Douglas Fir Will not accept chemicals even after incising

Purchasing Wood

• Consequently, you should avoid purchasing these species– As a rule, manufacturers will use the wood that

is most cost effective for them to treat, and it just takes to much effort to get a good retention figure with anything other than the three we listed before

– So you wont often run into treated Douglas Fir– It is still wise to look

Buying Hardware

• When purchasing fasteners and hardware, look for hot dipped, galvanized or stainless steel nails, screws, hinges, etc.– These will resist corrosion, and they won’t stain

your project with rust streaks– When nailing, drive nails at a slight angle

through the top board into the receiving board

Buying Hardware

– Vary the angle back and forth• This will help “hook” the lumber together, and

lessen the chance of a board working loose

• You may also want to use a nail set to avoid making hammer marks -- “smiles” in the surface of the wood; and a drill to drill pilot holes to prevent narrow boards from splitting

Buying Hardware

• Nail the boards -- especially decking or flooring boards -- “bark” side up.– You can determine the bark side by looking at

the end of a sawn board to see which way the annual rings curve

– The bark side will always be above the crown of the rings

Buying Hardware

• By nailing the bark side up, the bark will shed water better– This, in turn, helps inhibit the board’s tendency

to cup– And should some cupping occur, the board

won’t have raised edges that form “tow-stubbers” and “heelcatchers.”

Buying Hardware

• While you’re building, remember that the wood will still retain some moisture and will shrink after some months have passed– The original green color of most treated lumber

will not remain forever, so don’t fret if you dislike it

– After six months of weathering, the green will begin to face to a pleasant silver-gray color and remain that way

Buying Hardware

– Some manufactures use a CCA solution that’s been tinted with a brown dye, to make the stock more visually pleasing.

– But this doesn’t last either– Even these brown boards fade to silver-gray

after a few months out in the weather– If you want some other color than gray, just

wait a few months and paint or stain the wood to suit yourself

Prevention Maintenance

• Using pressure-treated lumber will prevent the ravages of insects and decay on your carefully planned, laboriously constructed outdoor project

Prevention Maintenance

– To get the best results, you need to choose the materials that best suit the project; work with the materials as they are intended to be worked with; and, above all, follow a few simple precautions to keep you and your environment safe from the possible effects of toxic chemicals.

– If properly used, outdoor lumber will poison the bugs and the fungi, but nothing else

Questions??

Designing and Building Stairs

• Basic Stair Types

• Designing a stairway

• Definitions

• Layout

• Carriage dropping

• Tread and Risers

• Stair assembly

Basic Stair Types

• Cleated stairway– Simplest, relies on wood or metal cleats

fastened to the carriages to support the treads (ever-loosening cleats)

• Wood cleats– Are 1X4’, screwing them over nailing. Angle-

iron cleats last longer. Used in the back porch and cellar

Basic Stair Types

• Open-tread stairway– Without risers, uses dadoes carriages.– The treads have 1/2 inch or more bearing on the

inside face of the carriages, and they are either nailed or screwed in place

• Use a circular saw, set depth of cut to half the thickness of carriage and make parallel cuts

• Utility stairs (porches and decks)

Basic Stair Types

• Cut-out Carriages– Basements

• Finished Stairway – Patient finish work, less tedious to build with

cut-out carriages hidden below the treads

• Treads and risers are scribe to the skirts

Questions?

Designing a stairway

• Comfort– Stair width

– Headroom• Basement 6ft 6 in

• House 6 ft 8 in

• Code– Maximum rise of 8 1/4

in and a minimum tread width of 9 in

– Riser + tread = 17.5 (a 7-in riser + a 10.5-in tread = 17.5 in)

– Riser X Tread = 75 (7*10.5=73.5)

Designing a Stairway

• Safety– Each tread should

project over the riser below it. No more .25 in and no less than 1 in.

– Handrails should be between 30 in and 34 in above the nosing with 1.5 in clearance between the handrail and the wall

• Cost

Questions?

Definitions

• Balusters– The posts or other vertical members that hold

up the handrail, usually 2 per tread

• Balustrade – The complete railing, including newel posts,

balusters and a handrail. Most of these parts are available as stock finished items at lumber yards

Definitions• Carriages

– Also called stair stringers, stair horses or stair jacks. They are the diagonal members that support the treads. Carriages can either be finish stringers or rough stringers - for an outside stairway, or for an inside stairway hidden from view

• Rough carriages are cut-out carriages, dadoes, or cleated stairs, made of 2x10 or 2x12 softwood lumber

• Finish stringers are usually made of 3/4 in or 1.5 in stock. Either cut out or routed

Definitions

• Closed Stairway– Stairs with walls on both sides. In this case a

wall stringer, whether it is a housed stringer or just a stringboard, is nailed to each wall. Closed stairways use handrails, not a balustrade.

• Finished Stairway– Any of several interior stair types that have

risers, treads, stingers and a handrail or balustrade

Definitions• Handrail

– This rail runs parallel to the pitch of the stairs. It’s held by balusters or brackets

• Headroom– the vertical distance from the lowest point of the

ceiling or soffit directly above the stair to the nosing line, an imaginary diagonal connecting the top outside corners or treads. Most codes requires at least 6 ft 8 in for stairs in living areas and 6 ft 6 in for basement utility stairs

Definitions

• Housed stinger– The profile of the treads, nosing and risers is

routed into a finish stringer. Extra room is left for wedges to be driven and glued in between the stringer and the treads and risers. Rabbeted and grooved risers and treads are Also used

• Landing– A platform separating two sets of stairs

Definitions• Newel post

– The large post at the end of the handrail. There is a starting newel at the base of the stairs, and a landing newel at turns.

• Nosing– The rounded front of the tread that projects beyond

the face of the riser 1 in to 1.25 in. In the case of open-tread stairways, it shouldn’t exceed .5 in. In most cases, the nosing is milled on the tread stock. On open stairways, a half-round modeling called return nosing is nailed to the end of the tread

Definitions

• Open or mitered stringer – This is cut-out finish stringer used in open

stairways. The treads carry over the stringer, but the vertical cut-outs on the carriage are mitered with the risers at 45 degrees.

• Open stairway– This can be open on one or both sides, requiring a

balustrade. In finished stairways, the open sides will use a mitered or open stringer

Definitions• Rise

– The height of each step from the surface of one tread to the next. Just as in roof framing, this measurement is sometimes called the unit rise. Many codes call for a maximum rise of 8.25 in. The height of the entire stair, from finished floor to finished floor, is the total rise

• Riser– Describes the rise of one step. It is also a stair part-the vertical

board of each step that is fastened to the carriages. Risers for a housed stringer stair are rabbeted at the top to fit the tread above, and grooved near the bottom for the tread below. Other stairs use a 1x square-edged stock. Open-tread stairs don’t have risers

Definitions

• Run– Also called unit run, this is the horizontal

distance traveled by a single tread. A 9-in run is the code minimum for main stairs. Total run is the measured distance from the beginning of the first tread to the end of the last tread-the horizontal length of the entire stairway

Definitions

• Stairwell– The framed opening in the floor that incorporates

the stairs. Its long dimension affects how much headroom the stair has

• Stringboard– Diagonal trim, not used to support the treads,

that is nailed to the stair walls. Finished treads and risers butt these. Often called skirt boards, backing stringers, or plain stringers

Definitions

• Tread– It is both the horizontal distance from the face

of one riser to the next, and the board nailed to the carriages that takes the weight of your foot. Exterior stairs, typically use 2x softwood treads. Interior stairs use either 1.5 in hardwood stock milled with a rabbet and groove to join it to the risers, or 13/16 in square-edged stock. Both are usually nosed

Definitions

• Winder– Wedge-shaped treads used in place of landing

when space is cramped and a turn is required in the stairway. Many building codes state that treads should be at least the full width of the non-winder treads. 12 in from their narrow end; or that the narrow end be no less than 6 in wide.

Questions?

Layout

• To lay out the carriages use the Pythagorean theorem (a2 + b2 = c2)– Add the width of an extra tread to your total run

to get enough length for the bottom riser cut

• Douglas-fir is the best lumber for the job because of its strength

• To draw the cut-out lines use either a framing square or a pitchboard

Questions?

Carriage Dropping

• Dropping the carriage is one of the most difficult things about stairs– What you marked on the carriage is the top of

the treads, but since you will be nailing treads to the carriages, you need to lower the entire member enough to make up for the difference

– If they sit on a finished floor such as a concrete basement slab, the bottom riser will need to be cut shorter by the thickness of a tread

Carriage Dropping

– This will lower the carriage so that when the treads and upper floor finish are added, each step will be the same height. The bottom riser will have to be ripped to a narrow width

– If the treads and floor finishes are of equal thickness and the carriage sits on the subfloor at the bottom no change will have to be made for the risers to be equal

Carriage Dropping

– When the treads are thicker that the finished floor draw a four-riser layout at any scale, on graph paper to figure how much of a drop you need to make and if the bottom riser needs to be narrower

– Give the carriage a trial fit before sawing it out.• The treads should be level from front to back and the

carriage should fit on both sides of the opening

• Make sure the risers will all be the same height once the treads and finish floor are installed

Carriage Dropping

– For cut-out carriages use a circular saw as far as you can and finish them off with a handsaw held vertically so as not to over cut the line and weaken the cut

– Nail the triangular cutouts to a 2x6 for a third stringer as a budget cut

– Use the completed carriage as a pattern to trace onto the other 2x12 and then cut the pencil line to get an exact duplicate

Questions?

Tread and Risers

• On a closed stairway the cut-out carriages sit inside the finished wall stringers, called skirtboards or strings

• 1x10s nailed hard against the wall so that the snug fit of previously installed risers and treads aren’t spoiled by the skirtboards spreading

Tread and Risers

• Install parallel to the noising line as high as possible

• Oak is best for treads but pine may be used

• Standard thickness for treads are 1 1/8 in and 13/16 in

• Crosscut risers and treads 1 in longer than the inside dimension between the skirt boards

Tread and Risers

• Risers will need at least a 45 degree miter to mate with the open stringer– use a radial arm saw or handsaw for this

Questions?

Stair Assembly

• Stair assembly usually begins at the bottom– First two risers are fit and nailed and then the

first tread is pushed tightly against the bottom edge of the riser for scribing

– Treads are initially cut to overhang the open stringer by the same dimension as the nosing

– A cross-grain section is cut out so that a mitered corner is left at the outer edge

Stair Assembly

– With a 1 in allowance for scribing set the scribers at 1/2 in for the first side

– Set the tread or riser with the side you are going to scribe down in place on the carriage and against the skirtboard

• The other end will ride high on the other skirt• Snug the riser along its entire length

– Get the inside dimension at the back of the tread or lower edge of the riser depending on which you are fitting

Stair Assembly

• Remember you can always plane it off but you can’t stretch it

• Risers and treads are nailed to carriages with 8d finish nails through predrilled holes

• Three or four 6d common nails through the bottom of the riser into the back of the tread will keep stairs together

Stair Assembly

• Two 1x1 blocks 2 in long glued behind each step at the intersection of the upper edge of the riser and the front of the tread will cut down a lot on movement too

• Any gaps between the carriage and treads should be shimmed from behind with wood wedges to eliminate squeaks

Questions?