102017315 Cultured Marble Making

CASTING: Cast Polymer

Composites

Applications Guide

Part Seven, Chapter IICopyright 2008

In This Chapter:1. Introduction

2. Materials

3. Molds

4. Manufacturing Process

5. Trouble Shooting Guide

6. Supplies for Marble Production

1. INTRODUCTION—This section will focus on thecountertop and bathware industry, most commonlyreferred to as Cast Polymers. Cast polymer products areused in commercial, residential, industrial, and medicalareas. The cast polymer product line has extendedbeyond the original kitchen and bath markets. Examplesof cast polymer products are vanity tops, sinks, bathtubs,shower pans, wall panels, countertops, windowsills,flooring, bar sinks, interior and exterior facades,banisters, and furniture, with the list continuing to grow.There are three distinct product lines within castpolymers:

• Cultured Marble—gel-coated surface, filled withcalcium carbonate, usually pigmented and/orveined, opaque in appearance.

• Cultured Onyx—gel-coated surface, filled withaluminum trihydrate, usually veined with anonpigmented background, and translucent inappearance, showing depth like natural onyx.

• Cultured Granite—gel-coated surface, filled withspecially designed granite filler to produce amulti-colored speckled appearance.

An unlimited variety of colors, cosmetic designs, andshapes that can be manufactured or fabricated providecast polymer products with distinct advantages over theirnatural counterparts. In addition, natural products areporous (which can become a source of bacterial growth)and can easily be stained, while cast polymer productsare not porous and are stain resistant.

2. MATERIALSA. Gel Coat—For cast polymer products ofcultured marble, onyx, and granite, the use of gelcoat is required. Gel coat is not used with solidsurface products. It is a polyester coating that isapplied to the mold surface and becomes an integralpart of the finished product. The function of gel coatis to protect the part from its environment, providingchemical resistance, water resistance, andweathering resistance (UV stability). The gel coat isalso accountable for the part’s cosmetic surface anddurability. It is the gel-coated surface that is visibleand therefore a critical aspect of the part.

Both pigmented and clear gel coats can be used toproduce cast polymer products although clear gelcoats are generally more popular.

Pigmented gel coats are mainly used to producecultured marble. Parts produced with pigmented gelcoats are solid colored. The pigmented gel coatforms an opaque coating and hides the color of thematrix poured behind it. Pigmented gel coats used incultured marble are formulated similarly to thoseused in open molding.

Clear gel coats add depth and dimension to the partand allows artistic colors and designs in the matrix tobe viewable. In cultured marble, clear gel coatprovides the ability to view vein patterns in thematrix. Clear gel coat is required with onyx toaccentuate the translucency and depth of theveining to more closely resemble natural onyx. Cleargel coat is also required to show off the multi-coloredeffect of granite filler.

Cultured granite can be manufactured using one oftwo methods:

1) Granite-effect filler is mixed into the resinand poured behind a clear gel coat.

2) Specially designed spray granite chips aremixed with a specially designed clear gelcoat and then sprayed onto the mold.Standard marble matrix is poured behind it.

Cook Composites & PolymersP.O. Box 419389 Kansas City, MO 64141-6389

Ph: (816) 391-6000 Fax: (816) 391-6125www.ccponline.com

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CASTING: Cast PolymerCopyright 2008

MATERIALS/ Gel Coat continued:

Clear gel coats used in the cast polymer industry arespecifically formulated for cast polymer applications.Key differences from clear gel coats formulated forother industries are lower color and slower curerates. Clear gel coats to be used with spray granitechips also have different viscosity and spraycharacteristics.

To meet performance requirements of bathwareproducts both pigmented and clear gel coats mustbe based on ISO/NPG polyester resins. Please referto Part Four, Open Molding for additional informationon gel coats.

B. Resin—Casting resin is mixed with fillers tomake the matrix. The matrix gives the cast part itsstructural integrity. Resin suppliers formulate castingresins from several components, including thepolymer, reactive monomer, promoters, inhibitors,and specialty additives. The specific componentsand amounts used are dictated by the end-useapplication, manufacturing process, required curebehavior, end-use physical properties requirements,and manufacturing plant conditions. Plant conditionscan dictate that resin gel time and/or viscosity bevaried to account for seasonal temperature changes.

Unsaturated polyester polymers are the basis ofcasting resins. Cultured marble, onyx, and graniteresins are based on orthophthalic polyesters.Cultured marble resins can also be based on hybridpolyesters. Because of color constraints, hybridpolyesters are generally not acceptable for culturedonyx or granite. (For additional information on resinchemistry see Part Three, Chapter II.)

There are several advantages to using hybridmarble resins versus orthophthalic marble resins :

1) Hybrid resins are inherently lower inviscosity and higher in solids content.This is an advantage when reportingemissions (HAP and VOC content) forpermit requirements.

2) Hybrid resins have superior filler wettingcapabilities which allow higher filler loading.This helps to reduce material cost byreducing resin percentage in the matrix.

3) Hybrid resins tend to develop green strengthand cure faster.

4) Hybrid resins have lower peak exotherm andshrinkage rate.The low shrinkage rate reduces the build-upof internal stress during the cure of the part,which improves the part’s thermal shockresistance. Also, because of the lowexotherm and shrinkage, hybrid resins areideal for making large parts such as tubsand shower pans.

5) Hybrid resins are very compatible withlightweight fillers.

The monomer fulfills two roles in the polyester resin.First, it reacts and cross-links with the unsaturationsites in the polymer to form the cross-linkedthermoset material. Second, it reduces the viscosityof the polymer to workable levels. The most commonmonomer used in casting resins is styrene.

Promoters, also called accelerators, split theperoxide catalysts used to cure casting resins intofree radicals. These free radicals attack theunsaturation sites in the polymer, preparing them forreaction with the monomer. Promoters used incasting resins determine the cure behavior and alsohave a significant impact on the color of the finishedpart. In general, the higher the promotion level thedarker the cured resin color. As a result, the typesand amounts of promoters used in casting resinsvary depending on the production speed and colorrequirements for each application.

• For cultured marble, the matrix is usuallypigmented or poured behind pigmented gelcoat, making the cured resin color lessimportant than for some other applications.As a result, marble resins are typically highlypromoted for faster cure.

• For cultured onyx and granite, clarity andlow-cured casting color are critical factors.Cultured onyx cannot be pigmented asheavily as cultured marble because it willreduce its translucency. As a result, onyxand granite resins have very low promoterlevels and correspondingly slower curerates.

• Swing or dual-purpose resins are acompromise between marble and



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MATERIALS/Resin continued:

onyx/granite resins. Swing resins contain ahigher level of promoters than onyx/granitebut less than marble. The result is lowercured casting color than cultured marble butfaster cure rates than onyx/granite. For mostmanufacturers, the small sacrifice in curedcolor is worth the increased speed ofproduction with onyx and granite products.In many cases, the color difference is notnoticed. The slower cure of swing resins incultured marble applications can beaddressed with catalyst. Manufacturers thatdo not want to buy separate resins formarble and onyx/granite applications alsouse swing resins.

Inhibitors provide shelf life stability to casting resinsas well as help control the working time or gel time.Free radicals generated in the polyester resin duringstorage or after addition of peroxide catalyst reactpreferentially with the inhibitors. Only after all theinhibitors are consumed does the cross-linking orcuring process begin.

In addition to the above materials, a number of otheradditives can be used in casting resin formulationsto affect properties. These include processing aidssuch as air release agents and wetting agents.Additives can also be used to affect the product’sperformance, such as UV absorbers and lightstabilizers for weathering performance.

C. Fillers—The filler is the largest part of the castpolymer composition. The type of filler to be useddepends on the cast polymer product.

1) Cultured Marble

a) Calcium Carbonate (CaCO3)—Typicalmarble filler is calcium carbonate(ground limestone). CaCO3 is minedand ground into small particles. Its sizeis measured in units called mesh. Fillerparticles are sorted through screenswith different size openings. Mesh sizeis designated by the number of holesper linear inch, with lower numbersindicating a coarse or large particle sizeand higher numbers indicating a fine orsmall particle size. CaCO3 fillers are

supplied as ‘all coarse’ or ‘all fine’particles or as preblended bags ofcoarse and fine particles.

A mixture of particle sizes of filler isused to provide maximum loading, withcoarse at 40 to 200 mesh and fine at325 mesh. Fine particles fill in betweencoarse particles so that resin-rich areasare reduced and higher filler loadingscan be achieved. For temperaturesbelow 85°F, a mix ratio of 2 parts coarseto 1 part fine provides excellent loadingproperties while avoiding warpage andcracking problems. For temperaturesabove 85°F, a mix ratio of 3 partscoarse to 2 parts fine will maintain thesame matrix viscosity.

b) Dolomite—Just like CaCO3, dolomite isa mined mineral, a mixture of calciumcarbonate and magnesium carbonate. Itis supplied just like CaCO3. Dolomite ismore abrasive than CaCO3 andtherefore may require more equipmentmaintenance.

c) Lightweight Fillers—The use oflightweight fillers in cast polymerproducts has been steadily increasing.Lightweight fillers are hollow spheresmade of glass (silica) or plastic. Theyoccupy space or volume but do not addweight, which effectively reduces theweight of a given part without changingits dimensions. Lightweight fillers areused with CaCO3. They can be boughtseparately or preblended with CaCO3 toa known weight displacement. Typically,these fillers demand a higher resinpercentage for wet out and to maintain aflowable viscosity. Also, because of itsinsulating effect, lightweight fillers causethe exotherm of the curing part toincrease.



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2) Cultured Onyx

a) Aluminum Trihydrate (ATH)—The fillerof choice for cultured onyx, ATH is a by-product resulting from the processing ofbauxite minerals in the manufacturing ofaluminum. Onyx grade ATH is muchbrighter white than CaCO3, thuseliminating the necessity of usingbackground pigment. It is a semi-translucent granular filler which providesa visual effect like natural onyx and hasthe added feature of acting as a flameretardant. At temperatures of 410°F(210ºC), ATH releases its waterparticles, slowing combustion andreducing smoke generation.

b) Lightweight Fillers—The use oflightweight fillers is not recommended incultured onyx since this would reducetranslucency.

3) Cultured Granite—Granite effect fillers aregaining in popularity. Filler suppliers havespecially formulated colors and particle sizedistributions to achieve a multi-coloredspeckled granite appearance and to give theproduct a cosmetic textured look. Thecolored granules may be coarse groundminerals or synthetically made frompigmented resins. The resin demand willvary greatly depending on the granulesize(s) and distribution. There is a differencein granite-effect filler mixed into the matrixversus spray granite filler mixed into the gelcoat and sprayed; therefore, method ofapplication needs to be noted whenpurchasing these fillers.

While inexpensive initially, if not chosen andchecked properly, fillers can become extremelycostly. For example, if too much coarse filler is usedand subsequently settles, a resin-rich area will resulton the back side which could cause warpage. If toomuch fine filler is used, the viscosity will be veryhigh, resulting in air entrapment. If the fillers containtoo much moisture or become damp, they will affectthe gel and cure.

Lot-to-lot variations and contamination of fillers can

also affect the cured casting color. There can besignificant particle size variations from lot-to-lot asshown in the analysis in the first chart on thefollowing page.

Each lot should be checked as soon as it isdelivered to determine if these factors will affect gel,cure, color, and matrix viscosity. To make thisdetermination, make a part with the new filler andcompare it to parts made with the lot already in use.Do not wait until time to switch to a new lot. Fillersshould be checked in conjunction with the resin fortheir effect on matrix color, gel time, viscosity, andcure properties.

D. Catalyst/Initiator—Catalyst is the componentneeded to ‘harden’ the polyester resin mix into asolid mass. Technically, catalyst causes the reactionbut does not participate in the reaction. In thecomposites industry, the correct term is initiator,which starts the reaction and is consumed by thereaction. There are three common types of roomtemperature initiators used in cast polymers:

1) Methyl Ethyl Ketone Peroxide (MEKP)—Themost widely used initiator, MEKP is a clearliquid that easily mixes into the resin. It is themost cost-effective choice and is available indifferent strengths to give a variety of curingcharacteristics. Recommended range is 0.5percent to 3 percent catalyst level based onresin amount.

2) 2,4-Pentadione Peroxide (2,4-PDO)—Alsoknown as acetylacetone peroxide (AAP),this initiator offers fast cure time and highpeak exotherm. Although it does lengthengel time, Barcol hardness builds quickly.Typically, 2,4-PDO is used during the coldertemperatures. It is available separately orpreblended with MEKP; however, preblendsare the most popular. When blended, theMEKP controls the rate of the gel time andthe 2,4-PDO provides the faster cure rateand higher peak exotherm. Recommendedrange is 1 percent to 2 percent catalyst levelbased on resin amount. Above 2 percent,2,4-PDO peroxide may inhibit cure. The onlydisadvantage with this initiator is that withsome resins, cured casting color may have ayellowish tint.



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Catalyst/Initiator continued:

Sieve Size Lot A% Lot B% Lot C

%

40 1.5 1.75 1.5

60 7 6.5 6.5

80 6.5 6.7 7.5

100 7 10 10.5

120 7 7.25 4

150 6 12 6

200 19.5 19.75 30.5

Through

200

45.5 36.75 33.5

3) Cumene Hydroperoxide (CHP)—CHPlowers peak exotherm and lengthens geland cure times. Lower peak exothermreduces cracking, crazing, and shrinkagebut also slows down Barcol development.CHP is most popularly used during hottertemperatures and/or on thick parts likeshower pans and tubs. It is availableseparately or pre-blended with MEKP;however, preblends are the most popular.

Some control over gel and cure rates can be achievedby changing initiator levels and blending the abovementioned initiators. Initiator level should be maintainedbetween 0.5 percent and 3 percent with 1.25 percentbeing the norm. Initiator levels below 0.5 percent maycause curing problems. Levels of 0.5 percent shouldonly be used during hot ambient temperatures where theheat will serve as a secondary catalyst or in large massproducts (e.g., tubs) where higher exotherms will begenerated because of the part’s thickness. Initiator levelsabove 3 percent are at the point of diminishing return,

with very little improvement seen in relation to the use ofthe higher amount. If the initiator level is excessive, theinitiator will cancel itself out to the extent that thereaction will stall. As the initiator level moves outside therange of 0.5 percent to 3 percent, change should bemade to a cooler or hotter initiator strength. Once thischoice has been exhausted, a different gel time versionof the resin should be ordered from the resin supplier.

3. MOLDS—The mold determines the shape, texture,and gloss of the finished part. It is a mirror image of thepart, so any defect in the mold will be reflected in all thecastings made from that mold. Simple molds have onesize and shape. Custom parts require specialdimensions so dividers and moveable bowls provide theflexibility to cast these one-time needs. Holding them inplace can be done with double-face tape, suction cups,clamps, hot glue, or other ingenious methods. Providingcosmetic transitions, such as a small radius where thefloating bowl or divider bars meet the deck, can beaccomplished using wax fillets or clay.

NOTE: Different clays vary in formulation, and withsome, there may be technical problems that can showup as fisheyes, pre-release, or that simply cause cureproblems with the gel coat. One way to reduce theseproblems is to dust the applied clay with baking soda orfumed silica. Then make sure to blow off the excesspowder before applying the gel coat.

A. Mold Materials—A number of materials can beused to make a mold. The most common are shownin the table below.

B. Mold Configuration— Vanity top molds aremodular or custom. Modular molds are fixed-size,one-piece, seamless construction with bowls, backsplash, and any special features built in. Custommolds may have built-in back splash but bowls anddividers are separate parts and positioned asdesired.

Vanity top molds include the following accessories:

1) Drain Plug—Usually made of polyethylene,the drain plug measures 1.75 inches indiameter. It can be permanent or removable.It serves to form the drain hole andattachment point for an overflow assembly(if used). The plug is attached to the bowlduring set up before gel coat application.



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2) Overflow Assembly—Although not requiredby the national plumbing codes, overflowsmay be needed for some specificapplications. A permanent plastic draincollar and tube may be encapsulated andremain in the bowl or a reusable flexibletube may be retrieved from the cured part.The tube attaches to the bowl and drain plugand should be installed after gel coat isapplied. The end connected to the drain plugshould remain unattached until after gelcoating for easier gel coat application to thebowl. This will allow the critical area of waterimpingement to be easily gel coated to theproper thickness. The overflow tube shouldbe spaced at least 1/2 inch from the bowlsurface to help prevent cracking.

Mold Type Advantage Comments

Fiberglass Easy to make

Long lasting

Can be textured

Radii can be built

in

Easy to repair

Easy to handle

Easily customized

Type most often used

Stainless

Steel or

Chromed

Steel

Durable

Hard surface

Smooth finish

Expensive

Deep scratches and

dents not easily

removed

Formica or

Melamine

Easy to make

Can be textured

Inexpensive

Not long-lasting

Not durable

Surface finish is fair

Glass Perfectly flat

Low maintenance

For flat panels only

Care must be taken

not to crack or scratch

the surface

3) Faucet Plugs—These form one-inchdiameter holes for faucet installation. Plugsmay be solid knockouts (re-usable) orcardboard rings that remain in the part.Plugs may be placed on wet gel coat to be

held in position when the gel coat cures.Clay can also be used to hold them inposition.

4) Female Hat—The hat functions to hold thematrix in place to form the bowl’s wallthickness. It is contoured to the male bowlmold and allows for overflow assembly (ifused). It is usually constructed withfiberglass, polyethylene, or polystyrene.Fiberglass and polyethylene hats arereusable (removed from part). Polystyrenehats are permanent (remain on the part).Hats may be full or partial. Full hats areusually used with modular molds. Full hatscompletely cover the mold and can beclamped in place for the one-pourproduction method. Partial hats aresometimes used with modular molds andalways on custom molds since these moldswill differ in bowl location. Partial hats coverthe bowl only and are used in the two-pourproduction method.

C. Polyethylene Dividers—These are often usedto custom-size flat areas, such as wall panels, backsplash, and vanity decks, into various shapes orsizes.

4. MANUFACTURING PROCESS

A. Overview—The 12 steps listed in the followingtable provide a very general outline of themanufacturing procedure for cast polymer:



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Overview continued:

Step # Action

1.Prep and set up molds.

2.Apply mold release agent to the molds.

3.Spray gel coat onto the mold.

4.Remove gel coat overspray from mold flange while

gel coat is still wet. This is easily done by applying

masking tape on the flange before gel coating and

then removing the tape after gel coating.

5.When the gel coat is ‘castable,’ apply matrix (resin,

filler, catalyst, pigment) to the gel-coated mold.

6.During the process of transferring the matrix into

the mold, a variety of veining techniques can be

applied to achieve the final cosmetic appearance of

the part.

7.Vibration is added to level the matrix in the mold

and remove air bubbles from the gel-coated

surface.

8.Remove excess matrix from the mold flanges after

the matrix gels but before it shrinks.

9.When possible, remove the back hat, open the

back splash, and eliminate any other constraints on

the part.

10.Demold the part as soon as possible to avoid

internal stress fractures.

11.After demolding, place the part on a supporting

surface to retain its shape during cure. If it is a solid

surface product, it is recommended the part be

postcured.

12.Once cured, the part is finished (trimmed, sanded,

and polished) and repaired (if necessary).

B. Mold Preparations and Maintenance—Themold determines the texture, smoothness, and glossof the finished part. It is imperative that the mold bekept in optimum condition. New molds must bebroken in following the directions of theirmanufacturer. (If building a mold, refer to Part Eighton Polyester Tooling for suggestions regardingprocedure.) Molds for marble will last through theproduction of many parts and provide maximumperformance if good mold maintenance is practicedand good workmanship is used in producing themold.

A mold maintenance program is essential in amarble shop to ensure the long life of polyestermolds. While it sometimes suffices to rewax a moldwhen it starts pulling hard, CCP has found thatproblems such as sticking and polystyrene build-upresult from neglect of the mold over time. CCPsuggests a routine mold prep schedule. It is farbetter to prevent polystyrene build-up with a good,consistent preventive maintenance program than toallow molds to get into bad shape.

To determine the prep schedule, start bydetermining how many pulls (parts) it takes for themold to start sticking. Then routinely prep and waxthe mold before this number is reached. Forexample, if the mold starts to pull hard and gloss isdiminished after seven parts are pulled, then alwaysprep and rewax the mold after pulling the sixth part.With careful adherence to such a program, moldswill last longer and produce better-looking parts withless patching.

The mold prep area should be completely enclosedand away from the production area. There should beisolated stalls for grinding and a separate area forgel coating.

Mold build-up should not be confused with what wasonce referred to as ‘wax build-up.’ Wax build-up ismore correctly stated as ‘wax leave-on” because thebuild-up occurs when excess wax is not buffed off.In fact, mold build-up is styrene (polystyrene) thathas come from the production gel coat. It adheres tothe mold mainly for these reasons:



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Mold Preparations and Maintenance continued:

• Wax leave-on• Pulling parts too soon (the more ‘green’ a

part when pulled, the more susceptible it isfor styrene to adhere to the mold)

• Too many parts made in the mold withoutproper maintenance

Normal mold preparation involves machine polishingthe mold with a glaze. If the mold is very hazy andhas some polystyrene build-up, a coarser compoundshould be used and followed with the glaze. Themold should be washed and rinsed with cold waterto remove compounding dust and compoundvehicle.

Some compounds can cause sticking if left on themold. Six fresh coats of mold wax should follow thewater wash. The fish eye and prerelease tendencywill always be greater after this fresh wax. However,if the gel coat is sprayed to a thickness of 18 to 20mils, the fish eyes should be covered, andprerelease tendency is minimized.

If the mold has a lot of build-up, it must be removedby scrubbing with a commercial stripper (toluene,methyl ethyl ketone, ethyl acetate, or ‘wax off’). Donot use styrene for cleaning molds. All of thesecommercial strippers are flammable and healthhazardous. Safety precautions should be observed:

• Read the Material Safety Data Sheet(MSDS).

• Wear gloves.• Wear safety glasses.• Make sure the area is well ventilated.• No smoking.

After molds have been stripped, if there is stillroughness on the mold surface, then the moldshould be sanded with sandpaper no coarser than600 grit and polished. If roughness or scum is left onthe mold, it will permit quicker mold/polystyrenebuild-up when put back into production. If using apolymer mold release system, follow supplier’sinstructions. Too much polymer mold release willcause fish eyes in the gel coat.

For more information, please refer to Chapter VIII,Mold Maintenance, in Part Eight on PolyesterTooling.

C. Gel Coat Application—Application of gel coatis the most critical aspect of cast polymer productionsince it provides the ultimate first impression of theproduct. Also, performance of the finished product isdirectly related to how well the gel coat is applied.For information on spray equipment and technique,please refer to Chapter II, Conventional Gel Coat,Section II.4, Application, in Part Four on OpenMolding.

Clear marble gel coats, specifically designed for castpolymer, and pigmented gel coats should be used inproduction of cast polymer. Typically, gel coat issprayed in a wet film thickness of 16 to 24 mils. Forparts that are not as critical (for example, wallpanels), the minimum wet film thickness isacceptable. For parts with high exposure to waterimpingement, the maximum wet film thickness isrecommended. It is important that the gel coat isapplied evenly throughout the part, therefore the useof mil gauges is encouraged.

Film gel time must be long enough to allow levelingand air release but short enough to prevent thestyrene in the gel coat from attacking the releasebarrier between it and the mold surface. If the lattersituation occurs, it would cause release impairmentleading to cracking and edge peeling or stress andshrink lines. Likewise, if the gel coat thickness isinsufficient, the styrene in the marble matrix canpenetrate the gel coat into the mold release andcause similar problems. Thin gel coat also may notcure thoroughly.

The gel coat is allowed to partially cure beforemarble mix is poured. Cure times are normally 30 to90 minutes depending upon plant temperatures,catalyst level, and air movement. Slight airmovement speeds cure by moving styrene vapor offthe gel coat surface. Styrene vapor does inhibit gelcoat cure. Forced air ovens, set at 100°F to 120°F,can reduce the gel coat cure time to a range of 15 to20 minutes. Uneven heat, too much heat, extendedtime, and too little or too much air movement in theoven may cause pre-release.

NOTE: Gel coats are flammable. Ovens used mustbe designed to accommodate flammable materials.



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D. General Matrix Formulation—Listed aregeneral starting points for each product line. Asproduction continues, the matrix formulationbecomes customized to each manufacturer.

1) Cultured Marble

Resin

CaCO3

Base

Pigment

Initiator/

Catalyst

22 - 26%

74 - 78%

0.5 - 1.5%

0.5 - 3.0% (based on resin content)

Resin recommendation of 22-26% is baseon orthophthalic polyester resin. If usinghybrid based marble resin,the starting resinrecommendation is 20-24%.

2) Cultured Onyx

Resin

Onyx Grade

ATH

Initiator/Catalyst

26 - 30%

70 - 74%

1.0 - 3.0% (based on

resin content)

Due to finer particle size ATH filler, culturedonyx requires higher resin content thanmarble to wet out and to reduce matrixviscosity to aid in air release. Due to thetranslucency of this product, it is necessaryto release as much air as possible (unlikeopaque cultured marble where it is onlycritical to remove the air from the gel coatsurface). Catalyst level is higher than marbledue to the lower promoter level of onyxresin.

3) Cultured Granite

Granite Matrix (granite mixed into the

matrix)

Resin

Granite Effect

Filler

Initiator/Cataly

st

22 - 30%

70 - 78%

1.0 - 3.0% (based on

resin content)

Resin content varies greatly with graniteeffect fillers depending on the particle size

and distribution of the granite particulates.The larger the granite chips, the lower theresin content. The finer the granite chips, thehigher the resin content. If the mix is tooloose (too high in resin content), the largerparticulates will fall to the gel coat surfaceand not achieve the desired appearance. Ifthe mix is too thick, air bubbles will betrapped in the matrix. Initiator/catalyst levelwill also vary greatly depending on thegranite color(s) being cast. It is advisable tokeep a log of initiator/catalyst level versusgranite color for reference.

Spray Granite (granite mixed into the gel

coat)

Clear Gel Coat

Spray Granite

Effect Filler

Initiator/Catalyst

50 - 60%

40 - 50%

1.5 - 2.0% (based on resin

content)

Unlike granite filler mixed into the resin andpoured behind clear gel coat, spray granite isgranite filler mixed with a specially formulatedclear gel coat and sprayed as the gel coat.Standard marble matrix is poured behind it.There is a difference in appearance betweenthese two methods of processes. As above,there is a wide range of gel coat/resin contentdue to the particle size and distribution of thegranite particulates. Please refer to the previousnotes on Granite Matrix.

It is a common practice to use marble clear gel coatas the carrier for the spray granite. The advantage isin not having to stock another product. Thedisadvantage is that gel coat is designed to cure inthin films and therefore is very reactive. To get thecoverage or ‘hide’ of spray granite, 20 to 30 mils filmthickness is required. Depending on granite particlesize, thicker film thicknesses may be required. If thelayer is too thin, the matrix behind it will showthrough. At 20 to 30 mils film thickness, standard gelcoat may cure too fast and exotherm too high,resulting in a variety of problems such asprerelease, excessive shrinkage, distorted



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Cultured Granite continued:

surface, etc. Specially formulated gel coat hasbeen developed to resolve this issue. Theadvantage is that the specially formulated gelcoat is very highly thixed to help suspend thegranite particulates and will cure at a muchlower exotherm than standard clear gel coats.The disadvantage is in having to stock anothermaterial.

The typical application process for spray graniteis to:

• Apply 10 to 12 mils of wet clear gel coatto the mold (this will give the finishedproduct a smooth glossy surface andadd depth to the finish appearance).

• Wait for the gel coat layer to dry to atacky finish, then spray on 25 to 35 milsof the wet spray granite mix (gel coat orresin plus spray granite effect filler).

• Wait for the spray granite layer to dry toa tacky finish, and then pour on themarble matrix (it is recommended topigment the background of the marblematrix the same general color as thespray granite for cosmetic purposes).

There are differences between granite effect fillersintended to be mixed into the matrix versus spraygranite intended to be mixed into gel coat. Makesure to specify to the supplier which product isneeded.

E. Matrix Mixing Methods—There are severaldifferent methods for mixing the matrix (incorporatingthe resin, pigment, catalyst, and fillers). If possible,add and mix the catalyst to the resin first beforeadding the filler. Mixing in the catalyst first willensure even distribution of the catalyst throughoutthe mix. Also, if adding separate fine and coarsefillers, mix in the fine or lightweight fillers first sincethey are more difficult to wet out before the coarsefillers. When using dry pigment, make sure thepigment is well-mixed into the resin before addingcatalyst. If dry pigment comes into direct contact withcatalyst, it creates a gaseous reaction that will leavemany air voids in the matrix.

1) Hand Batching/Small Batching Method—Materials are manually measured and mixedin a batch mixer, making 100 to 400 poundsof matrix per batch.

a) Premeasure all ingredients first.b) Add measured resin into mixing pot.c) If adding background color, add pigment

to the resin. Mix for one minute. Add asmall amount of filler to help dispersethe pigment.

d) Add catalyst to the pigmented resin. Mixfor one minute.

e) If using lightweight filler, add to themixing pot and mix until all is wet out.

f) If using separate fine and coarse fillers,add fine fillers first. Mix until all is wetout. Then add coarse filler and mix untilall is wet out.

g) Scrape down sides and mixing blade forunmixed material.

h) Mix for additional three minutes toensure thorough mixing.

i) Add veining pigment(s) if desired.j) Pour onto molds.

2) Auto-Dispensing Method—Auto-dispensingequipment is designed to deliver measuredamounts of resin and filler into the mixingpot. The primary advantage is that mostauto-dispensing units have resin heatingcapability that allows higher filler loading.This equipment eliminates the labor andtime previously required for measuringmaterials, delivers consistent materialquantities, and reduces material costs byheating up the resin to increase fillerloading. Maintenance is critical. As for anymachine, calibration should be performedregularly to ensure proper delivery ofmaterial amounts.

a) Operator chooses preset formulationand enters batch size into the machine.

b) Heated resin is dispensed into themixing pot.

c) Catalyst may be added by hand or bymachine. Mix for one minute.



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Matrix Mixing Methods continued:d) Add background pigment by hand and

mix for one minute. May add smallamount of filler to help disperse thepigment.

e) Machine dispenses filler into the mixingpot. Mix until all is wet out.

f) Scrape down sides and mixing blade forunmixed materials.

g) Mix for additional three minutes toensure thorough mixing

h) Add veining pigment(s) if desired.i) Pour onto molds.

3) Auto-Casting Method—As the namesuggests, auto-casting equipment isdesigned to measure, mix, and dispensematrix directly onto the mold. The machineis programmed with a formulation. Itmeasures the heated resin, filler, catalyst,and background pigment. The materials are

dispensed into a tube called the barrel. Inthe barrel, there is an auger screw thatserves as the mixing mechanism andtransports the matrix through the tube.Veining pigment, if desired, may beautomatically added as the matrix nears theend of the barrel or may be hand-applied tothe mold. Once the matrix emerges from thebarrel, it falls onto the mold or can be put ina bucket and then hand-poured onto themold.

Like the auto-dispensing equipment, auto-casting equipment has resin heatingcapabilities which allow higher filler loading.The whole process is automated, reducingthe labor force. Matrix output is high, greaterthan 50 pounds per minute, which increasesproduct output. Finished product should beconsistent. No need for measuringmaterials. Keeping the machine calibrated iscritical.

Matrix Viscosity Temperature Vibration

• Thick matrix will produce

crisp sharp veins.

• Thin matrix will produce

blurred veins.

• Hot temperatures will decrease

or thin the matrix viscosity.

• Colder temperatures will

increase or thicken the matrix

viscosity.

• Long vibration time will produce blurred or less defined

veins.

• Short vibration time will produce crisp, sharp veins.

• It is important to keep the vibration time constant in order to

maintain consistent appearance.

F. Veining—Veining is an art that becomes anidentifying mark for each manufacturer. Veiningtechniques vary as widely as the resulting designs.No one method is better than another, it is purely asubjective preference.

The table below lists some factors that will influenceveining results.

G. Pouring Methods—Transferring the matrix fromthe mixing pot/bucket to the mold can be done usingpaddles, scoops, gloved hands, or simply pouringout of the bucket. Pouring method, again, is thepreference of the manufacturer based on thecosmetic appearance of his product.

In general, the veined matrix is applied on the moldfirst. Once the vein pattern is established, the

remaining matrix is transferred and fills up the mold.

1). Pouring Vanity Tops/Bowls

a) One-Pour Method—The full hat, in thiscase with a lip that covers the wholemold, is positioned and clamped intoplace to stop matrix leakage. The rest ofthe mold is then filled as necessary.Some techniques utilize overfilling of themold areas, followed by quicklyclamping down the hat to force the extramatrix into the bowl area of the hat.Vibration is continued an additional fiveminutes to ensure air removal.

b) Two-Pour Method—This method isrequired with partial hats. It is similar to



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Pouring Methods continued:

the one-pour up to the point of adding thehat. Also, the initial pour can be a higherviscosity because the semiclosed moldsituation in single pouring, which hampersflow and air release, is not a factor. Crisperveining will result. Once the cavities of thedeck are filled, along with a matrix cover of1/8 to 1/4 inch on the bowl area, a hat with a3 to 5 inch lip is positioned around the bowlarea only. This may be removable orpermanent. Once the first pour has gelledand has enough strength to hold the hat inplace to prevent leakage, the second mix ismade to fill the cavity of the hat. This mixcan be lower in viscosity to allow it to flowmore easily. It may be any color as it will notshow through the first layer of marble.

The second pour, to fill the hat, may beadded shortly after the first pour gels, or itmay be delayed until after the first pour hasexothermed. Timing of the second pour isimportant. If either pour shrinks significantlywhile the other pour is soft, cracking canresult. The catalyst level of the second pourmay be reduced to delay and lowerexotherm development.

2) Pouring Large Parts (tubs, shower pans,etc.)—Tub castings can present uniqueproblems because of their mass. The largerthe mass, the higher the exotherm duringcure. The high exotherm may lead toexcessive shrinkage and cracking. Tubsmay also vary in wall thickness, which canlead to differential shrinkage and cracking. Athicker area may begin shrinking and createa tear or crack if adjacent to a thinner, lesscured area. Tubs are often cast in multiplepours, which are catalyzed at different times.

The following are points to consider incasting tubs:

Catalyst Level

• Catalyzation should be appropriate for the

ambient temperature.

• Catalyst levels may range from 0.5 percent

in the hot summer months to 1.25 percent in

the cold winter months. The norm is approx-

imately 0.75 percent (based on resin

content).

• Low catalyst levels coupled with variable

thickness can contribute to cracking due to

low green strength development.

Special Formulated Tub Resins

• Tub resins are high viscosity versions of

marble resins. (With higher viscosity, there is

less styrene monomer in the resin.)

• Lower styrene content reduces the amount

of shrinkage during the cure.

• Also, it is desirable to have thick matrix

viscosity for tubs so that the matrix will

adhere to the mold during the mold filling

process.

Demolding

• Remove the hat as soon as allowable to

dissipate the exotherm.

• Suspend the mold so that the part is right-

side up one inch above the floor to allow

gravity to aid in demolding the part.

• Demold the part as soon as possible to

alleviate any stress on the matrix.

H. Vibration—The effect of vibration is a result oftime, frequency, and amplitude. Frequency is therate at which vibration occurs. Amplitude is thepower or energy of the vibration. Ideally, vibrationcauses the mold and matrix to resonate at thevibration frequency. Heavier parts and mold candampen the amplitude and make the vibrationineffective. Likewise, the vibrator motor can makeloud noises but not actually transfer its power(amplitude) to the mold. It is recommended to



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Vibration continued:

periodically check the effectiveness of the vibratormotor.

Vibration is used during the process of filling themold to help the matrix flow over the mold surface.As the matrix moves, filling the mold, air bubbles areable to come to the surface and break. Once themold is filled, the vibration continues to help theentrapped air move off the gel-coated side andmigrate to the back of the part.

Vibration should commence during the filling of themold and stop several minutes after the mold isfilled. Vibration should never continue once thematrix has gelled. Excess vibration can wash out thevein pattern and cause the filler to settle to the moldside, which can contribute to warping. If air bubblesare seen on the gel-coated side, it may be due toineffective vibration or vibration time that is too short.

I. Demolding—Once the matrix has gelled, themold should be trimmed. This requires removal ofthe tape, the overspray gel coat, and the matrix fromthe mold flange. This helps the gel coat to releasefrom the mold and reduces the potential problem ofedge peel. As the part cures and begins to shrink, itis good practice to remove the back hat (of a bowl),open the back splash, remove inserts, and eliminateother constraints as soon as possible. Do not forcethese parts off because that will stress and possiblycrack the part. During the curing process, the matrixwill release or shrink away from these parts and itsremoval should be relatively easy.

Demold the part as soon as possible to avoiddeveloping internal stress as the part shrinks on themale mold. In extreme cases, it is possible for thepart to shrink and lock itself onto the male mold. Asstated before, do not force the part out of the mold. Itshould release on its own. If it requires too muchenergy or pressure, then the part is not curedenough to come off. When working with large partssuch as tubs, the mold can be suspended upsidedown to allow gravity to demold the part.

Once the part is demolded, it should be supportedon templates or tables to reduce the possibility ofwarping while it is completing its cure. This isespecially critical if the demolded part is still very

‘green’ (flexible or soft).

J. Finishing and Repairing—Once the part iscured, it will need to be finished. Typical finishingincludes:

• Sanding the edges and the back orbottom of the part (smoothing off thesurfaces)

• Polishing the top surface (gel-coatedside)

• Drilling or smoothing the edges of thefaucet and drain holes

• Repair or patching of surface defects

If the defect is in the gel coat only, patch using thegel coat. If it is deeper, use catalyzed matrix almostto the surface. After it cures, patch with the gel coat.With granite or solid surface, repair using the matrixmix.

K. Influence of Temperature—Gel and cure of thegel coat and matrix are influenced by many factors;for example, catalyst levels, catalyst type, humidity,types of fillers, and pigments can shorten orlengthen gel times. Gel and cure rates can bemanipulated by variations of catalyst type and level.The use of higher catalyst levels produces faster geltimes but will also produce hotter cures. The use oflower catalyst levels produces slower gel times butwill also lengthen total cure times.

The most influential factor and the hardest to controlis temperature. Often, attention is given to thetemperature of the resin, but temperatures of thefillers, mold, and room are neglected. If the resin iswarmed to 100°F (38ºC) and it is mixed 75 percentwith filler at 50°F (10ºC), the combined matrixtemperature will be approximately 60 to 70°F (15 to21ºC). The gel and cure is further inhibited bypouring the matrix onto a 50°F (10ºC) mold sitting at50°F (10ºC) ambient temperature.

Heat is another catalyst to the cross-linking reaction.The exotherm generated by the reaction is neededto help drive the cure through. If the ambienttemperature and the materials are cold, theexotherm is lost to heating its surroundings. In coldtemperatures, viscosity of matrix thickens, curetimes are extended, and degree of cure issues andair entrapment problems are predominant. As



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Influence of Temperature continued:

ambient temperatures go up, matrix viscositydecreases and high exotherms and inconsistentshrinkage become the main problems. As catalystlevels and resin contents are lowered to account forthe higher temperatures, the green strengthdevelopment becomes affected, which can lead tocracking or tearing problems.

A crack is characterized by a sharp straight line andis primarily due to excessive shrinkage caused byhigh exotherms. Cracks can be controlled byreducing catalyst level and optimizing the filler toresin ratio. A tear will have a haphazard directionand is ‘whitish’ in color and appears in areas ofmaximum stress. Tears are primarily due to poorgreen strength development.

A mix will hold significantly more fillers at highertemperatures. For example, a resin adjusted to1,500 cps when used in a mix of 23 percent resin,and 26 percent fine and 51 percent coarse fillers hasa viscosity of 344,000 cps at 77°F (25ºC). The samemix at 99°F (37ºC) is only 152,000 cps and is toothin to be workable. Often times, mixing viscosity isfine-tuned by adding resin or filler. In this case,adding more filler will bring up the viscosity. As thisis done, resin percentage can drop to the pointwhere green strength development is significantlyslower, which can result in edge peel, stressing, andpossibly tearing of the part.

A recommended procedure would be to alter thecoarse-to-fine ratio to maintain proper matrixviscosity while maintaining the original resin content.It is advisable when using a two-component fillersystem to increase the percentage of fine fillerduring the hotter temperatures. A standard mix usinga two coarse-to-one fine filler ratio will require 2percent additional filler at 99°F (37ºC) versus 77°F(25ºC) to keep the same viscosity. At ambienttemperatures over 85°F (29ºC), fine fillers should beincreased to a ratio of three coarse-to-two fine fillers.If preblended fillers are used, it is suggested to keepbags of fine fillers available for such adjustments.

Another alternative to keeping mix viscosity constantwithout changing filler ratios at higher temperatureswould be to use higher viscosity resins. From themanufacturing side, whatever opportunities are

available to keep materials as cool as possibleshould be used. Problem parts should be cast duringthe coolest point of the day. Starting earlier andfinishing earlier for summer hours to take advantageof cooler mornings deserves strong consideration.

5. TROUBLESHOOTING GUIDE—This section providessome possible causes or explanations for typicalproblems encountered during production of cast polymerproducts.

A. Filler Particle Packing—Filler particle packingrefers to the distribution of the individual fillerparticles within the matrix. The looser thedistribution, the larger the spaces between particles.The tighter the distribution, the smaller the spacesbetween particles. Use of all coarse or large fillerparticles results in the loosest distribution ofparticles. Use of a combination of coarse and finefillers results in the tightest particle packing. See theFigure 7/II.1 and Figure 7/II.2 on the next page.

Tight filler particle packing in cast polymer productsenhances the performance of the finished part. Incast polymer products, resin fills in the gapsbetween particles. If the gaps are large enough, theresin may shrink and pull away from the fillerparticles creating small fissures within the matrix.This is referred to as resin laking. The fissurescaused by resin laking may go unnoticed until stressor impact, such as thermal cycling, causes it to opento a visible surface crack.

Filler particle packing and particle size also affectthe matrix viscosity. See Figure 7/II.3 on the nextpage. Use of all coarse filler particles will result inhigher viscosity due to poor packing. Use of all fineparticles will result in high viscosity due to poorparticle packing and high resin usage. Again a blendof coarse and fine particles is ideal. Use of two partscoarse and one part fine fillers will yield the lowestmatrix viscosity.



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Figure 7/11.1 - Poor filler particle packing.

Figure 7/11.2 - Good filler particle packing.

Figure 7/11.3

B. Temperature—Temperature affects theviscosity of the resin which can lead to changes inthe resin content of the matrix. The higher thetemperature, the lower the viscosity; the lower thetemperature, the higher the viscosity. Examples of

viscosity versus temperature relationships for tworesins are shown in Figures 7/II.4 and 7/II.5 on thenext page. Low temperatures affect the viscosity

Figure 7/11.4 - Viscosity poor filler particle packing data.

Figure 7/11.5 - Good filler particle packing data.

Figure 7/11.16



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Temperature continued:

much more dramatically than high temperatures.The higher the original resin viscosity the moretemperature changes will affect the viscosity.

Temperature also affects the matrix viscosity. SeeFigure 7/II.6 on the next page. Starting with resin at1,260 cps viscosity and blending 25 percent resinand 75 percent filler, the resulting matrix has a200,000 cps viscosity. When the temperatureincreases to 95ºF (35ºC), the 1260 cps resinviscosity can thin down to 600 cps. To get the same200,000 cps matrix viscosity using the 600 cpsviscosity resin, the matrix composition will be about22.7 percent resin and 77.3 percent filler. This is a2.3 percent resin reduction in the matrixcomposition. While 22 percent resin is acceptable,care must be taken if resin percent gets too low (lessthan 20 percent). Too low resin content may lowerthe finished product’s performance, such as thermalshock.

C. Cracking and Tearing—As temperaturesincrease, cracking and tearing problems will alsoincrease.

Cracks (sharp straight lines) are primarily due toexcessive shrinkage caused by high exotherm.

Tears (lines which are haphazard or lack direction,and may have frayed appearance) are primarily dueto low green strength* and will appear in areas ofmaximum stress.

Cracking and tearing can be avoided by adjustingfiller ratios in relationship to increases intemperature.

As temperature increases:

DO

NOT

Increase filler percent to increase matrix

viscosity.

- Increased filler percent will lower the

resin percent.

- Lower resin percent will reduce green

strength* development which can lead

to tearing.

DO Maintain resin percent and increase ratio of

fine fillers.

- Standard filler mix is two parts coarse

to one part fine.

- At temperatures over 90°F, a ratio of

three parts coarse to two parts fine will

maintain original viscosity.

DO Switch to higher viscosity resin.

- Allows use of standard filler mix (two

parts coarse to one part fine).

D. Gel Coat Delamination—This situation occurswhen gel coat adhesion to the mold is so strong thatthe matrix is not able to pull the gel coat free fromthe mold as it shrinks; subsequently, the matrix pullsaway from the gel coat.

Some possible solutions for gel coat delaminationare as follows:

1) Improve the mold release application orchange mold release type.

2) Increase in catalyst level of the gel coat toaccelerate the cure time. This will preventthe styrene from dissolving the releaseagent and improve the cure of the gel coatand increase shrinkage.

3) Take care to ensure the gel coat is sprayedon 20 to 25 mils wet (cures to 18 to 20 mils).Thin films cure slowly.

4) Use a resin with faster green strengthdevelopment.

E. Gel Coat Delamination on Edges of Part—Gelcoat delamination on the edges of a part has twoprimary causes. These causes along with solutionsare described as:

1) Gel Coat Overspray—Overspray tends to bethin and cures at a slower rate. Flange areastypically are not waxed and gel coat doesnot easily release from the surface.Adhesion of the gel coat to the unwaxedflange area of the mold is stronger than theadhesion of gel coat to matrix at the edge.Thus, upon demolding, the gel coat will peeloff the marble matrix edge.



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Gel Coat Delamination on Edges of Partcontinued:

To avoid this problem, tape the flange areasup to the edge of the marble part. Afterspraying the gel coat, remove the tape whilethe gel coat is still wet.

2) Thin Gel Coat on Vertical Edge—Gel coaton a vertical edge may be thin, causing it tocure at a slower rate and not shrink awayfrom the mold.

To check for this problem, measure the milthickness on the vertical edge to ensure thatit is the same as the rest of the part. Also,increase the catalyst level of the gel coat toaccelerate the cure time.

*WHAT IS GREEN STRENGTH?

In a filled polyester system, green strength is the

strength development between gelation and the point of

peak exotherm (cure rate). This is measured by the time

required from catalyzation to a measurable Barcol

hardness.

Soon after gelation, the matrix begins to shrink. It is not

immediately apparent due to the adhesion of the gel coat

to the mold. During the shrinking process, the strength is

building up to a point when it is able to sufficiently

overcome the adhesion of the gel coat to the mold.

Hence, the part releases from the mold. If the shrink rate

exceeds the strength development, tearing occurs.

Slow green strength development may be caused by:

1. Slow reactive resin

2. Cold resin, fillers, mold, shop

3. Catalyst level too low or wrong type

4. Filler loading too high

5. Moisture in the fillers

6. Influence of pigment

F. Prerelease of gel coat on bowl perimeter andedges of parts—Prerelease of gel coat on bowlperimeter and edges of parts has a number ofpotential causes. These causes along with solutionsare described as follows:

1) Uneven Gel Coat Thickness—The gel coatmay be too thick in the creases due todrainage. These thicker areas will curefaster and have a higher shrink rate. Toavoid, check gel coat thickness whilespraying. Keep spraying as evenly aspossible (20 to 25 mils wet).

2) Motion—If using floating bowls which are notsecured, movement or vibration will causethe bowl and gel coat to move and releasefrom the mold surface. To avoid, make sureall mold parts and edges are secured.

3) Prerelease When Using Clay—When usingclay around the bowl perimeter and edges,oils from the clay can cause prerelease ofthe gel coat. Potential for this problem ismagnified in the summer months, as hottertemperatures soften the clay and releasemore oils to the surface. These oils serve asmold releasing agents to the gel coat. Takeone or more of these steps to avoid thisproblem:

a) Keep clay as cool as possible.When cold, the oils remain in theclay and are not drawn to thesurface.

b) After placing the clay on the mold,lightly sprinkle talc or powder on it toabsorb the oils. Be sure to blow offthe excess powder.

c) After placing the clay on the mold,put a layer of mold release on theclay; this will help seal in the oils.

d) Before applying the clay onto themold, draw the oils out of the claywith a microwave oven. Put the clayon an unwaxed paper plate or papertowel and microwave for 30 to 60seconds. The oils will come to thesurface and be absorbed by thepaper. CAUTION: If microwavedtoo long, the clay will become dryand crumble.



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G. Gel Coat Stress Lines—The main cause ofstress lines is high gel coat adhesion to the moldwhich causes incremental release instead of asmooth continuous release.

To avoid, check the following areas:

1) Mold Releasea) Make sure molds have good layer of

mold release.b) Be sure mold release is applied properly

over entire mold, including the edges.2) Gel Coat

a) Make sure gel coat is sprayed evenlyover part (20 to 25 mils wet). Rememberthat thin films cure slowly.

b) Catalyze gel coat to get reasonably fastgel and cure. Slow gel times will allowgel coat to dissolve release agents.Overcatalyzing will cause too muchshrinkage.

c) Check catalyst line of spray gun to makesure catalyst is not ‘spitting’ and makinghot spots. Thick films will cure andshrink more.

3) Matrix Shrink Rate Greater than Gel CoatShrink Ratea) Reduce catalyst level of matrix to slow

down gel and cure rate.b) Use lower shrinkage resin.c) Reduce lightweight filler amount.

Lightweight filler increases peakexotherm, causing higher shrink rate.

d) Increase filler loading.e) Check fine to coarse filler ratio. Too

much coarse filler will increase numberof resin lakes between fillers andincrease shrinkage.

H. Cracking and Delamination of White GelCoats —White gel coats (as opposed to clear gelcoats) are more heavily promoted and containtitanium dioxide (TiO2-white pigment). TiO2 inhibits(slows) the gel time; therefore, higher catalyst levelsare required.

Higher catalyst levels can lead to higher exothermthat in turn leads to exothermic cracking. On theother hand, if the catalyst level is not sufficient, thegel coat will cure very slowly. Upon curing of the

matrix, insufficiently cured gel coat may tear due tolow green strength and fail to release from the mold.

Once the gel process has occurred, because ofhigher promoter levels and extra catalyst, the curerate is quicker than with clear gel coats. If the gelcoat has overcured, the matrix will not bond well.Delamination will be further enhanced by the TiO2,which reduces the surface tack of the gel coat.

To avoid this problem, be sure to:

1) Determine the appropriate catalyst level.2) Be aware of the cure rate of the gel coat.3) Pour the matrix at the appropriate time.

I. Gel Time Too Fast or Too Slow—There arethree main factors that can promote too fast or tooslow gel time.

These influencing factors are:

1) Influence of Fillers and Pigmentsa) Change of filler sources.b) Change from coarse to fine particle

ratios (the more fine particles, theslower the gel time).

c) Moisture in filler (or resin) which willinhibit gel time.

d) Change in pigment colors andconcentration. Dark colored pigmentsand TiO2 inhibit gel time.

2) Influence of Temperaturea) As a rule of thumb, a resin temperature

increase of 18°F (-8ºC), will cut the geltime in half. A decrease of 11°F (-12ºC)in temperature will double the gel time.

b) Temperature of filler. If resin is warmand filler is cold, matrix is cold.

c) Mold temperatures. Cold molds will cooloff a warm matrix.

3) Influence of Catalysta) Change in catalyst supplier.b) Change of catalyst ratio.c) A change from or blend of MEKP

catalyst to 2,4-pentadione peroxide (2,4-PDO) catalyst, (i.e., Azox Trigonox-44).A 2,4-PDO catalyst will have a slowergel time but a faster relative cure.



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J. Too fast or too slow cure times have twoprimary causes. These causes along with solutionsare described below.

1) Influence of Pigments, Fillers, Temperature,and Catalysta) Any influence of the above factors that

affect gel time will also affect cure time.NOTE: Gel and cure times are directlyrelated. The faster the gel time, thefaster the cure time.

b) Use of lightweight fillers tends toincrease peak exotherm and cause afaster cure rate.

2) Casting Size and Thickness (the larger andthicker the part, the faster it cures and thehigher the peak exotherm)a) Lower the catalyst level or use a ‘cooler’

catalyst.b) Remove or open molds as soon as

possible.c) Use air or water to dissipate the heat

from the surface of the part.

K. Warpage—Warpage has two basic causes.These causes along with solutions are describedbelow.

1) Filler Settling—This produces resin-richbacks, which cure, shrink, and pull inwardcausing the parts to warp upward in themold. Solutions include:a) Increase fine filler particles to increase

or thicken the matrix viscosity.b) Increase total filler loading to increase or

thicken the matrix viscosity.c) Reduce vibration time to reduce the

chance of filler settling.d) Increase the catalyst level to shorten the

gel time.2) Excessive Shrinkage—Excessive shrinkage

causes warpage on the decks around thebowl. Solutions are described as follows:a) Increase filler loading. The lower the

resin content in the composition, thelower the peak exotherm and shrinkage.

b) Check fine to coarse filler ratio. Toomuch coarse filler will increase thenumber of resin lakes and increaseshrinkage.

c) Reduce the catalyst level. The longerthe gel time, the lower the peakexotherm.

d) If back-pouring the bowls, reduce thecatalyst level in the second pour. Theexotherm of the first pour will helpcatalyze the second pour.

e) Remove the parts from the mold whilestill warm and support it right side up tocounter the warpage.

f) Check mold release application to makesure it’s not a prerelease problem.

3) Post Demold Warpage—Warpage of partsafter demolding due to lack of full cure canbe avoided by the following:a) Lay the part down so that it is better and

fully supported until cured.b) Increase the catalyst level to quicken

the cure or try a secondary curingcatalyst such as a 2,4-pentadionecatalyst (Azox, Trigonox-44, etc.)

c) Check the mixing procedure and makesure the catalyst amount is bothmeasurable and a large enough quantityto ensure a good even distributionthroughout the matrix.

L. Cracking—Cracking is mainly caused byunrelieved cure shrinkage stress which exceeds thegreen strength of the resin. Solutions to this probleminclude:

1) Reduce Matrix Shrinkagea) Increase filler loading.b) Use lower shrinkage resin.c) Cure matrix slower by reducing or

changing catalyst.d) For tubs and shower pans, use higher

viscosity resin.2) Increase Matrix Crack Resistance

a) Increase green strength by doing one ofthe following:a1) Use hotter catalyst or increase

catalyst level.a2) Use 2,4-Pentadione type catalyst.

b) Increase matrix elongation.b1) Use higher elongation resin.b2) If using lightweight fillers, try using

lightweight fillers with added



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Cracking continued:elongation or glass fibers (e.g., R. J.Marshall Thermolite 100).

c) Relieve stress by allowing the part tomove as it shrinks.c1) Remove hats, open back splashes.c2) Check mold release.c3) Check gel coat gel and cure.c4) Check mold design.

M. Air Bubble Entrapment—Air bubbleentrapment has three possible causes. Thesecauses and suggested solutions follow.

1) Matrix Viscosity Too Higha) Check temperature of resin, fillers, shop,

and mold. The colder it is, the thickerthe matrix.

b) Check for high concentration of fine fillerparticles. The higher the quantity of fineparticles, the thicker the mix.

c) Increase the resin ratio of the mix.d) Use lower viscosity resin.e) Add wetting and air release agents to

the resin.2) Ineffective Vibration

a) Check for sufficient and uniformvibration force around the table.

b) Lower catalyst level to decrease geltime and allow more time for vibration.

3) Catalyst Reaction with Pigment and/or FillerGenerating Gas Bubblesa) Mix catalyst thoroughly into resin before

adding dry pigment and filler.b) Make sure all dry pigment and fillers are

thoroughly dispersed (no lumps) beforeaddition of the catalyst.

N. Soft Spots—Soft spots are caused by resin thathas not gelled or cured evenly. Possible solutionsare:

1) Increase catalyst levels, using lower-strength catalyst and increasing volume.

2) Mix catalyst to resin thoroughly beforeadding filler.

3) Check for moisture in filler (wet filler tends toclump; water retards gel and cure).

4) Check for pockets of unmixed pigment.

O. Blurred Vein Lines—Blurred vein lines are

caused by matrix mix that is too low in viscosity. Thisproblem can by resolved as follows:

1) Increase filler ratio.2) Increase catalyst level.3) Reduce vibration time.

P. ‘Guesstimating’ Resin Gel Time—Temperature versus resin gel time is an exponentialrelationship (see graph on this page). For example,if a resin gel time at 70°F (21ºC) equals 15 minutes,what would the gel time be at 60°F (15ºC) or 80°F(27ºC)? The formula is:

Use 60 – 70 = -10

Multiplying factor for -10 = 1.90 (see chart)

15 X 1.90 = 28.5

Gel time at 60°F (15ºC) = 28.5 minutes.

Use 80 – 70 = +10

Multiplying factor for +10 = 0.68 (see chart)

15 X 0.68 = 10.2

Gel time at 80°F (27ºC) = 10.2 minutes.

As a general rule of thumb, for every 11°F (-12ºC)

decrease in temperature, the gel time doubles (2x).

For every 18ºF (8ºC) increase in temperature, the

gel time halves (0.5x).



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RESIN GEL TIME GUESSTIMATOR

Temperature

Difference

Multiplying

Factor

Temperature

Difference

Multiplying

Factor

-2

-4

-6

-8

-10

-12

-14

-16

-18

-20

1.15

1.31

1.51

1.67

1.90

2.09

2.31

2.59

2.95

3.46

+2

+4

+6

+8

+10

+12

+14

+16

+18

+20

0.92

0.85

0.79

0.73

0.68

0.62

0.58

0.53

0.50

0.45

Q. Catalyst Ratio—Remember that increased

temperatures can cause high exotherms and increase

shrinkage, which will result in cracking. When

temperatures increase:

DO NOT DO

Reduce the catalyst

level.

- Catalyst amount

may be too small to

disperse thoroughly

in the mix.

- This will slow green

strength

development.

- Full cure may not be

achieved.

Change to a lower strength

catalyst.

- This allows an increase in

catalyst amount for better

mixing and to ensure full

cure.

Switch to a longer gel time

resin.

- Allows an increase in

catalyst percent or …

- Maintains ‘normal’

catalyst percent.

The general rule of thumb for catalyst ratio is that

the level should be maintained between 0.5 percent

minimum and 3 percent maximum.

As the catalyst level moves outside this range,

change, as appropriate, to a cooler or hotter catalyst

type.

6. SUPPLIES FOR MARBLE PRODUCTION—CookComposites and Polymers supplies gel coats, resins,and cleaners for cast polymer production. Otherresources are listed here:

A. Mold ManufacturersGruber Systems25636 Avenue StanfordValencia, CA 91355-1117Ph: 800-257-4070

661-257-4060Fax: 661-257-4791www.gruber-systems.com

J. R. Composites Inc.1251 GoForth RoadKyle, TX 78640Ph: 800-525-3587

512-268-0326www.JrComposites.com

Ken Fritz Tooling & Design, Inc.1945 Puddledock RoadPetersburg, VA 23803Ph: 800-426-1828

804-862-4155Fax: [email protected]

B. Filler SuppliersAlcan Specialty Aluminas6150 Parkland Blvd.Suite 220Cleveland, OH 44124Ph: 440-460-2600Fax: 440-460-2602www.Riotinto.com/riotintoalcan

Imerys100 Mansell Court East, Ste 300Roswell, GA 30076Ph: 888-277-9636

770-645-3700Fax: 770-645-3384www.imerys-perfmins.com

R. J. Marshall Company26776 W. 12 Mile RoadSouthfield, MI 48034Ph: 800-338-7900

248-353-4100



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Fax: 248-948-6460www.rjmarshall.com

ACS International4775 South 3rd AvenueTucson, AZ 85714Ph: 800-669-9214

520-889-1933Fax: 520-889-6782www.acstone.com

Huber Engineered Materials1000 Parkwood Circle Ste 1000Atlanta, GA 30339Ph: 678-247-7300Fax: 678-247-2797www.hubermaterials.com

Filler Suppliers continued:Sanco Inc.207 Brookhollow Industrial Blvd.Dalton, GA 30721Ph: 800-536-5725

706-279-3773

C. Dry Pigment and Pigment DispersionSuppliers

American Colors1110 Edgewater DriveSandusky, OH 44870Ph: 419-621-4000Fax: 419-625-3979www.americancolors.com

BroCom Corp.2618 Durango DriveColorado Springs, CO 80910Ph: 888-392-5808

719-392-5537Fax: 719-392-5540www.marblecolors.com

Plasticolors2600 Michigan Ave.P.O. Box 816Ashtabula, OH 44005Ph: 888-997-5137

440-997-5137Fax: 440-992-3613

www.plasticolors.com



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COOK COMPOSITES AND POLYMERS CO.

WARRANTIES, DISCLAIMERS, AND LIMITATION OF LIABILITY (Rev. 03/09)

Seller warrants that: (i) Buyer shall obtain good title to the product sold hereunder, (ii) at Shipment such product shall conform to Seller’s specifications; and (iii) the sale or use of such product will not infringe the claims of any U.S. patent covering the product itself, but Seller does not warrant against infringement which might arise by the use of said product in any combination with other products or arising in the operation of any process. SELLER MAKES NO OTHER WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE, EVEN IF THAT PURPOSE IS KNOWN TO SELLER, ANY APPLICATION INFORMATION OR ASSISTANCE WHICH SELLER MAY FURNISH TO BUYER IS GRATUITOUS AND SHALL IN NO WAY BE DEEMED PART OF THE SALE OF PRODUCT HEREUNDER OR A WARRANTY OF THE RESULTS OBTAINED THROUGH THE USE OF SUCH PRODUCT.

Without limiting the generality of the foregoing, if any product fails to meet warranties mentioned above, seller shall at seller’s option either replace the nonconforming product at no cost to Buyer or refund the Buyer the purchase price thereof. The foregoing is Buyer’s sole and exclusive remedy for failure of Seller to deliver or supply product that meets the foregoing warranties. Seller’s liability with respect to this contract and the product purchased under it shall not exceed the purchase price of the portion of such product as to which such liability arises. Seller shall not be liable for any injury, loss or damage, resulting from the handling or use of the product shipped hereunder whether in the manufacturing process or otherwise. In no event shall Seller be liable for special, incidental or consequential damages, including without limitations loss of profits, capital or business opportunity, downtime costs, or claims of customers or employees of Buyer. Failure to give Seller notice of any claim within thirty (30) days of Shipment of the product concerned shall constitute a waiver of such claim by Buyer, Any product credit received by Buyer hereunder, if not used, shall automatically expire one (1) year from the date the credit was granted. Notwithstanding any applicable statute of limitations to the contrary, any action by Buyer in relation to a claim hereunder must be instituted no later than two (2) years after the occurrence of the event upon which the claim is based. All the foregoing limitations shall apply irrespective of whether Buyer’s claim is based upon breach of contract, breach of warranty, negligence, strict liability, or any other legal theory.



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102017315 Cultured Marble Making

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