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Epoxy

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Understanding epoxies

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Epoxy

  1. 1. UNDERSTANDING EPOXY JANUARY 2000
  2. 2. Table of ContentsIntroduction .............................................................................................................................................................. 2Chemistry .............................................................................................................................................................. 2-4Industrial Formulators’ Epoxies ................................................................................................................. 4-5Safety and Handling ............................................................................................................................................ 5Measuring and Mixing Epoxy Systems ................................................................................................. 6-7Techniques of Epoxy Use .............................................................................................................................. 7-8Coating with Epoxy Resin ............................................................................................................................ 8-9Fiberglassing with Epoxy Resin ............................................................................................................. 9-11Using Fillers with Epoxy Resins .......................................................................................................... 12-13Epoxy Resins as Strustural Adhesives ............................................................................................. 13-14Filleting, Fairing and Molding with Epoxy Resins ..................................................................... 15-16Painting and Finishing ............................................................................................................................. 16-17Troubleshooting ................................................................................................................................................... 17
  3. 3. Introduction about the use of these products as outlined in this booklet is a distillation of the knowl-When you begin to work with epoxy resins, edge we have gained over the years. This isit’s always useful to know a little of their to help you, the user, to be in charge. Yourhistory. The dictionary defines epoxy as responsibility is to make sure that all the“heat setting resin made by the chemical products you use, including ours, are usedbonding of smaller molecules into larger properly. The section on chemistry mayones.” seem a bit of a mystery to some of you, but a rudimentary understanding will help youWhile that may be over simplifying things a complete your tasks more efficiently.little, in all epoxies, that is basically what ishappening. What becomes complicated is You’ll find here sections on basic chemistrythe thousands of variations that make each and safety regarding all epoxies. Properchemical compound used in the manufacture measuring and mixing techniques are next.of epoxy resin formulations specifically And we finish with a useful section ondifferent to perform the job it was designed troubleshooting.to do.Scientists have been aware of epoxy resins Chemistryfor many years but the first commercialexploration of their properties was undertaken A thorough knowledge of epoxy resinin the 1930’s. This was in Germany by the chemistry is not necessary before you start,firm of I.G. Farben Industries. However, it but having a basic chemical knowledgewas not until the 1950’s that use of the will help you complete your project morecompounds in a commercial way was effectively.introduced in North America. At about thistime the founder of Industrial Formulators, The resin that is the basis for most of ourJim Peters B.Sc., began experimenting with epoxy formulations is the diglycidol etherthem and over the years became one of the of bisphenol A (DGEBA). Bisphenol A isleading formulators in the world. produced by reacting phenol with acetone under suitable conditions. Bis means two,Epoxies are among the “thermoset” family phenyl means phenol groups and the “A”of resins, along with polyester, silicones, stands for acetone. Thus, bisphenol A is theurethanes, melamines, acrylics and phenolics. chemical product made from chemicallyOnce curing of epoxies has taken place combining two phenols with one acetone.they cannot be melted by heat. This makes Unreacted acetone and phenol are strippedepoxies the opposite of such other plastics from the bisphenol A which is then reacted(thermoplastics) like polyethylene, vinyl, with a material called epichlorohydrin. Thispolypropylene, etc., which can be melted reaction sticks the two (di) glycidyl groupsand solidified over and over again. on ends of the bisphenol A molecule. The resultant product is the diglycidyl ether ofIndustrial Formulators, Inc. supplies epoxies bisphenyl A, or the basic epoxy resin. It isfor industries such as construction, electronics, these glycidyl groups that react with themarine, automotive, sporting goods and amine hydrogen atoms on hardeners tohobbies. Our epoxy formulations have been produce the cured epoxy resin.used to solve problems and are used regularlyin pulp mills, submarines, dams, museums, Basic epoxy resin is very viscous andrailroads and research labs along with more unsuitable for use except as a thick gluestandard uses like boat building and electrical for specialized applications. At Industrialpotting. We are experimenting with new Formulators Inc., we purchase the materialuses for epoxy resins all the time. in this basic form, then modify it using formulae developed by us. The result isOur responsibility is to provide quality the various epoxy resin systems we offer.products to our customers. The information 2
  4. 4. Hardeners used with room temperature that can accommodate one, or by changingcured epoxy resins are most commonly the temperature and mass of the resin/polyamines. That is, they are organic hardener mix.molecules containing two or more aminegroups. Amine groups are not unlike ammonia The epoxy curing reaction is exothermic.in structure except that they are attached to This means that it gives off heat as it cures.organic molecules. Like ammonia, amines The rate at which the epoxy resin cures isare strongly alkaline. Because of this similarity, dependent upon the curing temperature.epoxy resin hardeners often have an ammonia- The warmer it is the faster it goes. The curinglike odor, most notable in the dead air space rate will vary by about half or double within containers right after they are opened. each 10°C (18°F) change in temperature.Once in the open this odor is difficult todetect because of the low vapor pressure For example, if an epoxy system takes 3 hoursof the polyamines. to become tack free at 21°C (70°F), it will be tack free in 1.5 hours at 31°C (88°F) or tackReactive amine groups are nitrogen atoms free in 6 hours at 11°C (52F). Everything towith one or two hydrogen atoms attached do with the speed of the reaction follows thisto the nitrogen. These hydrogen atoms react general rule. Pot life and working time arewith oxygen atoms from glycidol groups on greatly influenced by the initial temperaturethe epoxy to form the cured resin - a highly of the mixed resin and hardener.crosslinked thermoset plastic. Heat willsoften, but not melt a cured epoxy. The The gel time of the resin is the time it takesthree-dimensional structure gives the for a given mass held in a compact volumecured resin excellent physical properties. to solidify. Gel time depends on the initial temperature of the mass and follows theThe ratio of the glycidol oxygens to the above rule. Cure time is surface area/massamine hydrogens, taking into account the sensitive in addition to being temperaturevarious molecular weights and densities sensitive.involved, determines the final resin tohardener ratio. Varying the recommended What’s happening is this: as the reactionratio will leave either unreacted oxygen or proceeds it gives off heat. If the heat generatedhydrogen atoms depending upon which is immediately dissipated to the environmentside is in excess. The resultant cured resin (as occurs in thin films) the temperature ofwill have lower strength, as it is not as the curing resin does not rise and thecompletely crosslinked. reaction speed proceeds at a uniform pace. If the resin is confined (as in a mixing pot)Epoxy hardeners are not catalysts. Catalysts the exothermic reaction raises the temperaturepromote reactions but do not chemically of the mixture, accelerating the reaction.become a part of the finished product. Epoxyhardeners mate with the epoxy resin, greatly Working time is about 75% of the gel timecontributing to the ultimate properties of the for the size and shape of the pot. It can becured system. lengthened by increasing the surface area or working with a smaller batch. MaterialCure time of an epoxy system is dependent left in the pot will increase in absoluteupon the reactivity of the amine hydrogen viscosity measured at 24°C (75°F), foratoms. While the attached organic molecule example, due to polymerization but initiallytakes no direct part in the chemical reaction, decrease in apparent viscosity due toit does influence how readily the amine heating. Material left in the pot to 75% of gelhydrogen atoms leave the nitrogen and react time may appear quite thin (due to heating)with the glycidol oxygen atom. Thus, cure but will actually be quite thick when cooledtime is set by the kinetics of the particular to room temperature. Thick, partially curedamine used in the hardener. Cure time can epoxy is not as effective in wetting outbe altered only by selecting a different fiberglass cloth and bonding surfaces.hardener, adding an accelerator in systems Experienced users either mix batches that 3
  5. 5. will be applied almost immediately or exposure will induce chalking and eventuallyincrease the surface area to slow the reaction, the epoxy will disintegrate, losing itsthus increasing working time. mechanical properties. The solution to this problem is to protect the epoxy coatingAlthough the cure rate of an epoxy is with paint or with a varnish which containsdependent upon temperature, the curing an ultraviolet light shield.mechanism is independent of temperature.The reaction proceeds most quickly in the Caution must be observed when usingliquid state. As the cure proceeds the system epoxy resins along with polyester resins.changes from a liquid to a sticky viscous soft Observe the general rule that epoxy resinsgel. After gelation the reaction speed slows may be applied over cured polyesters thatdown as hardness increases. Chemical have been dewaxed and well-sanded butreactions proceed more slowly in the solid polyesters should never be used over curedstate. From the soft sticky gel the system epoxy resins. Unreacted amine in the epoxygets harder, slowly losing its stickiness. inhibits the peroxide catalyst in the polyesterIt becomes tack free and continues to causing an incomplete cure at the interface.become harder and stronger as time passes. Sanding does not get rid of the unreacted amine. The result is a poor bond evenAt normal temperatures the system will though the surface appears cured.reach about 60 to 80% of ultimate strength Debonding will be the inevitable result.after 24 hours. Curing then proceeds slowlyover the next several weeks, finally reachinga point where no further curing will occurwithout a significant increase in temperature. Industrial Formulators’However, for most purposes, room temperature Epoxiescured systems can be considered fully curedafter 72 hours at 25°C (77°F). Industrial Formulators’ epoxies are formu- lated systems, meaning that we start withIt is usually more efficient to work with as basic epoxy resins manufactured by largefast a cure time as practical for the application chemical companies and modify them toat hand. This allows the builder to get along make them suitable for the required end use.to the next phase without wasting time In the first modification (for most products)waiting for epoxy to cure. Faster curing films we reduce the viscosity by the addition ofwith shorter tack times will have less chance diluents or low viscosity solvents, which areto pick up fly tracks, bugs, and other airborne also epoxies. This makes an epoxy systemcontaminants. thin enough to wet fiberglass cloth, coat wood and bind various fillers to produce gapA surface film may form in some epoxy systems filling glues and putties. Because theduring the curing process. Technically, this diluents we use are also epoxies, they aresurface film is an amine carbamate that can called reactive diluents, reacting with theform in the presence of carbon dioxide and amines the same way the basic resin reacts,water vapor. More appears on cool damp becoming a part of the cureddays than on warm sunny days. This film system. Other materials protect against longis water-soluble and should be removed term embrittlement and im-with soap and water before sanding and prove resiliency and impact resistance.re-coating or painting. This occurs mainly Finally, trace materials designed to lowerwhen using 51-Cure or Cold Cure with surface tension, promote substrate wetJet Cure Hardener. All epoxies should be out, reduce cratering and “fisheye” forma-sanded lightly but thoroughly before tion, aid in breaking bubbles and detrainingrecoating, or recoated within 72 hours. air are used to produce the finished product.Unprotected exterior epoxy resin coatings These modifications are what make our epoxyare not ultimately sunlight resistant. After systems unique and different from others.about six months of exposure to intense We develop the chemical formulations for oursunlight they begin to degrade. Additional epoxy resins and hardeners. To ensure our 4
  6. 6. desired level of quality, all of our epoxy Keep Epoxy Resins and Hardeners off your skinproducts are produced in our manufacturing Wear disposable gloves or barrier skin creamsfacility. Every batch gets tested for both gel (available from Industrial Formulators Inc.)time and “thin film set time”. Nothing is when working with epoxy resins. Never useshipped to a customer that does not meet solvents to remove epoxies from your skin.our high standards. Everything we ship Solvents, in addition to having problems thatcures if properly measured and thoroughly are as bad or worse than epoxies, can helpmixed. drive the hazardous ingredients into your body. If accidental contact occurs, use aThe diverse background of our staff gives good handsoap and lots of water and paperus the unique advantage of knowing and towels to remove epoxy from your skin.applying epoxy technology far better than Then apply a good medicated skin creamothers in the business. The development, to replace the natural oils removed by themanufacture, and distribution of Industrial handsoap. Using a solvent to removeFormulators products is our only business, partially cured epoxy from your body isand our staff takes pride in being personally not an acceptable alternative.available to all of our customers. If a rash develops when working withThe dominant factor in the design, develop- epoxies you should stop until it clears up.ment, and evolution of Industrial Formulators If the rash is bad or persists see a doctor.products has been this: Take him a copy of this book and have himAn Epoxy System should adapt to the conditions of contact us if he needs additional information. Don’t continue to work with epoxy if youthe user - Not the other way around. break out every time you get near it. This is your body’s way of telling you to cool it. Pay attention. Safety and Handling Working cleanly and keeping epoxy off youWe select our resin and hardener raw are the keystones of epoxy safety. Work in amaterials with the health and safety of our throwaway mode. Don’t try to clean brushescustomers in mind. However, it is not with solvent - toss them out. Tools like puttypossible to make a hazard-free epoxy resin knives can be wiped with a paper towel thensystem. As with all chemical products, they sanded clean after the epoxy cures. Curedmust be handled properly to minimize epoxy doesn’t stick to polyethylene or waxhealth risks. Material Safety Data Sheets paper. Gloves, disposable brushes, and one(MSDS) are available upon request for time use roller covers are expendable. Yourall of our products. health is not. Think of gloves and dust masks as another part of the cost of the project,The primary hazard when working with an being prepared to spend some money onepoxy system is skin irritation leading to these items designed to help protect you.possible skin sensitization from prolonged We like the inexpensive disposable glovesand repeated direct skin contact. Most as opposed to heavier, more permanentpeople who become sensitized are unable gloves. The problem with the heavier glovesto continue working with epoxies without is that they eventually become contaminatedbreaking out in a rash commonly on the with uncured resin or hardener on the insideinside of the forearms and on the forehead long before they wear out. The very thingabove the eyebrows. The effect appears to be that you started using to protect you is now acumulative. That is, you might be able to get source of contamination. Disposable glovesaway with getting epoxy on your skin for wear out about the time they become dirtyawhile but sooner or later it can catch up to and are replaced.you and you will be sensitized. We wouldlike to emphasize that these products canbe used safely for a lifetime – if handledproperly. 5
  7. 7. The vapor pressure of epoxy resins and Develop a measuring technique that ishardeners is so low that vapors rarely cause sufficiently accurate and then stay with it.problems, unless you have already become Doing it the same way each time will minimizesensitized. Well-cured resin should cause no the chance for error. In the interest of simpli-problem, as it is largely inert. fication the following discussion assumes a 2:1 volume ratio. Refer to our catalog forWhenever sanding or creating any kind of specific product mix ratios.dust wear a mask along with safety glassesand gloves to keep the dust out of your If you are using some type of graduated cuplungs. If you sand fiberglass and allow the or a straight-sided can, get in the habit ofdust to get on your skin you will probably get measuring the same way each time. If youan itch from the glass fibers. Shower in cool pour the resin first, then always pour thewater to wash the fibers off you. The itch resin first. Before you add the hardener,usually goes away after 24 hours. notice how much resin is already in the container, divide this by two (for a 2:1Epoxy resins and hardeners have a low system) and then add hardener to bringflammability risk generally burning only if the total to the correct mark. Measuring inexposed to a high heat source. BUT, the the same order each time will avoid thesolvents found in S-1 and Titanium are common error of two parts of hardener toflammable, and vapors can even be explosive one part of resin.in the right concentration. Be smart andavoid any possible source of ignition when Using a vertically held stir stick marked in ausing solvents. two to one ratio will only work for vertical sided containers. Don’t use this method onMost people never develop health problems containers with sloping sides.working with epoxy resins. If we scared youa little then it’s our hope that you’ll work with If you use the “two measures/one measure”these materials a little smarter and cleaner method and mix in a separate pot, be surethan you might have otherwise. to scrape the sides each time you pour from your measuring cups to the mixing pot. Measuring and Mixing Make sure the graduations on disposable cups look right. Some paper cups are not Epoxy Systems rolled correctly when made – the first graduation sometimes is too high or too low.Measuring and mixing is really easy because We can’t inspect each cup to make sure itmost of our epoxy systems mix at a 1:1 or was properly made – this is your job.2:1 volume ratio. This doesn’t mean youdon’t have to pay attention to what you’re For small batches less than 90 ml (3 oz.)doing. Occasionally a customer will call use the syringes or accumeasure kit.suggesting that something is wrong withthe epoxy because it didn’t cure properly. Industrial Formulators Inc. offers oneWe know of no situation where the resin/ mechanical pump for those who desirehardener has gone bad or has been the convenience that is devices provides.contaminated and wouldn’t cure. It always These pumps are the kind that you find atresolves that the batch was either improperly the ballpark and use to get mustard out ofmeasured or insufficiently mixed in the the jar to put on your hot dog. Completeuser’s shop. Epoxy chemistry just will not instructions come with each plunger pumpallow it to work any other way. kit. We recommend using the pumps to dispense, not measure. Pump into a graduatedMeasuring errors are insidious and can pop mixing cup or tub to be double sure of anup when you least expect them. These errors accurate measure.usually occur because you changed yourtechnique, were in a hurry, had someoneelse mix a batch, or were just not careful. 6
  8. 8. Be aware that any mechanical device cango haywire, lying to you with a straight face. Techniques of Epoxy UseValves can stick causing backflow into thereservoirs. Cool temperatures can cause the Four epoxy application techniques areviscosity to change. The rate or speed that commonly used. These are coating,you pump can alter delivery volumes. fiberglassing, gluing and filleting/fairing. Furthermore, the techniques are pretty muchEpoxy systems can be measured by weight the same whether they are involved in woodas well as volume. The correct ratios vary so or fiberglass construction and repair. Afterif you plan to mix by weight give our technical all, coating with epoxy involves the samesupport line a call. Don’t make the mistake of technique and tools regardless of whetherusing the volume ratio when measuring by the substrate is wood, fiberglass, or some-weight. The hardener is less dense than the thing else.resin you’ll use too much hardener and getan incomplete cure. What might seem to be other techniques are usually just variations or combinations of theLarge batches (a litre or more) are most above. Many of our epoxy users discoverefficiently measured by weight. A postal new variations. We will discuss a numberscale is usually accurate enough for the of these variations and the “tricks” that willlarger batches. An O’Haus triple beam make the epoxy work go easier and faster.balance will allow for the accurate weighing We don’t know everything and are constantlyof batches from as little as a few grams to learning something new. We invite you toover 2.5 kilograms. learn along with us.With the resin and hardener accurately If you come up with a variation that we don’tmeasured, mix thoroughly. Stir well, scraping mention, model it first to see if it will work.the container sides, and mix from the bottom Do this prior to using the whole project as ato the top. Keep stirring until that mixture is test. For example, we are often asked if Coldno longer hazy. Don’t worry about a few air Cure epoxy will stick to stained wood. Mostbubbles. That’s normal. Scrape the mixing of the time it will if stain used is water orstick several times on the side of the container alcohol based. However, the only way to be really sure is to conduct your own little test.Don’t make large batches. Keep in mind thatlarge batches take longer to mix, have a Suppose that you are staining a piece of firmuch shorter pot life, and if you get side that will later be coated with epoxy and havetracked cost more when they gel in the pot. another piece laminated to it. First, stain aEpoxy paperweights are expensive. scrap piece of the same wood; allow it to dry well (several days). Laminate on two piecesIf you measured or mixed incorrectly and of 3 or 4 inch wide fiberglass tape abouta batch doesn’t properly cure about the fifteen cm long. Leave a “tail” that can beonly thing to do is scrape it off and start over. grasped later with a pair of pliers by runningA hot air gun will help to soften the partially the tape about half way up on a plasticcured material. Then try removing any squeegee. Let the epoxy cure a day or two.residual with acetone, MEK, or lacquer Remove the squeegee and grab the tail withthinner (but not with the hot air gun or the pliers. Try to peel the tape off the substrate.source of ignition around). Wear solvent If the tape tears where the tail starts leavingresistant gloves and have plenty of ventila- the balance of the tape bonded to the surface,tion when doing this. Then examine your then the bond is good. If the whole thingtechnique to find out what went wrong. pops off intact then the bond is bad and the stain is interfering with the bond strength. Better find a new stain and repeat the test. This same procedure can be modified to test the ability of the epoxy to bond exotic woods. If the failure occurs in the wood when two 7
  9. 9. pieces are glued rather than in the glue line pull away from the surface creating craters.then it is safe to assume that the epoxy Overheating will also cause the expansion ofworks on that kind of wood. any air in the pores of the wood and may result in an epoxy coating full of bubbles.In order to simplify the following discussionof the four main areas of use for our epoxy Sometimes a coating will try to crater. Thissystems we are going to confine the discus- is most common with coatings that are toosion to using Cold Cure epoxy with plywood, thin, recoated surfaces that have not beena common building material. Where appro- thoroughly sanded or on contaminatedpriate we will mention the use of our other surfaces but may happen on other surfacesepoxy systems. The sections following this as well. While the cause of cratering is quitewill discuss modifications of the four tech- complex, the solution is pretty simple.niques for specific areas of building and Immediately after coating a surface look atrepairing fiberglass structures. We feel that if it from an angle, sweeping your eyes overyou can understand and use the following the whole surface. Craters will usually formtechniques then you will be able to skillfully within ten minutes after first applying thedo most kinds of epoxy work. coating. If cratering occurs, take the heel of the foam roller and really grind it in the area that has cratered. This wets out the dry spotsCoating with Epoxy Resin in the crater center. Then, re-roll the area treated to even out the coating.Whenever possible it is best to do coatingoperations on the bench. If the part is too Cold Cure epoxy will bond and cure in thinlarge or cumbersome to place on the bench, coatings in cold, damp conditions withoutthen whenever possible arrange your work any special tricks, but giving it an inductionso that it is horizontal. When working flat period will help speed things along. Afteryou’re not fighting gravity and the coated mixing the resin and hardener allow the mixpanel is easily sanded on the bench using a to sit in the pot for 15 to 20 minutes. Thendisc sander and foam pad. Coating a sheet apply it in the usual manner. The use of a hotof fir plywood will illustrate this method. air gun will help level a cold epoxy coating but it is not necessary to aid in the cure.Mix the resin and hardener in the correctratio. Pour this mix on the plywood in a After 24 to 48 hours (depending uponstream of “S” curves starting at one end and temperature and hardener used) the coatingfinishing at the other, making four or five will be cured enough to sand. First wipe thecurves along the length. Spread the epoxy surface with a damp sponge to remove anyback and forth with a squeegee into the dry water soluble amine carbamate surface filmareas, trying to get as even a coating as prior to sanding (for Jet Cure or 51-Curepossible without being too fussy. Use a dry only). At this stage of cure the epoxy coatingfoam roller to even out the coating. When can usually be sanded with a disc sanderthis first coat is cured to at least a soft set and a big foam pad starting with 60 grittack free stage it can be recoated. paper. Disk sanding can generate quite a bit of heat, especially when the sandpaper getsUse at least two coats for interior wood and dull or clogged, causing gumming of thethree in areas that may be constantly wet. sanding disk. Keep the sander moving and apply only light pressure. This keeps theSeveral tricks can be used to improve the heat down. If clogging still happens you’llappearance of the finished film. Bubbles that have to either hand sand, scrape as describedpersist in the coating can be broken with a below, wet sand or allow another day for thefoam brush by lightly dragging it across the cure to proceed.surface. Fanning the uncured surface with ahot air gun or hair dryer will accomplish this Scraping is an alternative to sanding thatwith greater speed. Avoid overheating an actually produces a better finish. This shavesarea as this could cause the epoxy film to off a thin film of epoxy leaving a surface that looks like it was sanded with 600 grit paper. 8
  10. 10. Small parts can be scraped using a single more coats of varnish and is much moreedged razor held vertically. Several companies durable. Revarnishing is much easiermake wood scrapers for working on larger because the old varnish is just removedsurfaces. Keep them sharp and be careful down to the epoxy coating.not to cut yourself. Epoxy coatings should be sanded beforeSanding dust should be removed by blowing varnishing or painting. These materials stickor brushing it off prior to recoating. The final to the epoxy by mechanical means and mustbit may be removed with a damp rag. Don’t have some “tooth” in order to bond well.use acetone, or other solvents. Tack rags mayleave an unbondable surface coating on thesanded epoxy surface. Fiberglassing withSome amine cured epoxy surfaces are Epoxy Resinquite alkaline and can react with any acidicmaterial such as moist carbon dioxide or Exterior surfaces usually use fiberglass orsilicates. Further epoxy coats may not bond other woven cloth material as a reinforcement,well to some of these reaction products. or substrate, allowing a thicker, strongerSanding, in addition to providing some epoxy coating which results in higher“tooth” for mechanical bonding, also cleans abrasion, impact and moisture resistance.since it exposes new, uncontaminated In the case of most wood composite structures,surface. If in doubt, sand. the purpose of this reinforcing cloth is to strengthen the epoxy coating, not to reinforceTry to work at a constant or falling temperature the part.when coating. When the temperature isrising, air trapped beneath the uncured Cold Cure epoxy is a much better choiceepoxy may expand and cause small bubbles over wood than polyester resin. Polyesterto form in the coating. Avoid working in is a poor adhesive because it shrinks anddirect sunlight for this reason. If you must delaminates then it lets moisture get betweenwork in sunlight, do your coating as the sun the fiberglass and the wood substrates.is going down. The surface will be coolingand air bubbles should not form. Evening Because the fiberglass is structural to thedew condensation does not harm the epoxy coating rather than the part, it’spartially cured Cold Cure epoxy coating. possible to use a lightweight cloth. Don’t use a cloth a that is too heavy for the intendedSome very porous materials are quite service, you’ll use a lot more epoxy and havepersistent at forming air bubbles. A trick we a heavier part, gaining little else. Tests runhave used is to heat the whole surface to a with Cold Cure epoxy show no appreciabletemperature about 60°C (140°F). Use a hot difference in peel strength between the twoair gun or place the wood in the sunlight for most popular finishes of fiberglass cloth,awhile. Stop heating and immediately coat Volan and Silane. Four and six ounce cloththe surface. The epoxy will thin on the warm are nearly invisible when wet out with clearsurface and at the same time start to cool it. epoxy resin. Heavier weight cloths begin toThe air in small pores will begin to contract show the weave pattern under certainpulling the thinned epoxy into them. Any air lighting conditions.that does rise will be going through thinnedepoxy and have an easier time of it. Avoid using fiberglass mat with epoxy resins. The binder that holds the mat together isCold Cure is an excellent base for varnish. designed to be dissolved by the styrene inThe application of multiple coats of varnish polyester resins. Most epoxies don’t useand sanding between coats can be eliminated styrene as a diluent, making it almost impos-with NO sanding between coats. The final sible to wet out the mat. Woven roving is wetepoxy coat is sanded to provide a base, then out well by epoxy although we know of noone or two coats of varnish are applied. The reason to use it when building a wooden boat.result appears to have the depth of ten or 9
  11. 11. Regardless of the type of the cloth or resin When this first area has been covered andsystem used, fiberglassing is done essen- the cloth has disappeared, take the squeegeetially the same way. There is no need to be and use a fair amount of pressure to squeezeintimidated by fiberglassing, what you are the excess resin away from the wet cloth,really doing is gluing the cloth to the surface working it down into the dry cloth area.with a minimum amount of resin. Use just This removes excess resin and trapped air,enough epoxy to wet out the cloth, you’ll fill sticking the cloth down right next to thethe weave of the cloth later with more epoxy. wood surface. The squeegeed cloth should now have a semi-dry look with the weaveWork on as horizontal a surface as possible. pattern showing; the cloth itself will beFiberglassing is much easier if you are not invisible.fighting gravity. Keep on going, section by section, until youThe first step in doing a good fiberglass job are finished. If you are working on a veryis to precoat the part. This avoids the problem large area use a dry roller cover on theof having an unsealed porous structure soak previous three or four sections to give aup too much epoxy, starving the bond. final smoothing. On smaller boats the rollerPrecoating doesn’t use any more epoxy can be used after the entire hull has beenthan the more difficult one step method fiberglassed.(for experienced fiberglasser’s only!) andhelps to assure that maximum peel strength Let the epoxy resin cure to the “green state”is achieved. After the first coat cures fill any stage where it is pliable but no longer tackyholes with an epoxy/microballoon mixture unless pressed really hard. Now’s the timeto provide a smooth base for the cloth. to trim the excess cloth. Trim by running aSand lightly but thoroughly to a uniform dull single edged razor blade around where thesurface. Clean the surface with clean, oil free glass overhangs the edge. Press down anycompressed air or brush off and wipe with a glass that may be lifted from the surfaceclean damp rag to remove any remaining while trimming.traces of dust. We do not recommend usingacetone or similar solvents for this. Much The selvege edges of the fiberglass have toacetone sold today is reclaimed and may be feathered before being covered by anotherhave impurities that interfere with secondary piece of cloth. Wait another hour or so andbonding by leaving a film of residue on the do the feathering with a Surform. Do it whilesurface. it is in the right state of cure. Too early and the wet fiberglass will lift, too late and it willNext lay the fiberglass out on the precoated, be too hard to cut. The alternative is to waittack free surface, smoothing it out and doing a day or so until it is hard enough to sand.any rough trimming. Masking tape may benecessary to hold the cloth in place if the It is not always possible to have a selvagesurface has any slope. edge on the cloth. Rather than have a cut edge fraying all over the place which canMix no more than 300 ml of resin and 150 only be cleaned up by a lot of sanding later,ml of hardener. Work with small batches here’s a trick that produces a very neat edge.until you get the hang of it. Start at one end Run a piece of 2” masking tape so that theand pour the resin out over an area equal to inner edge of the tape is where you want toabout 50 ml per square ft. (450 ml does a stop the glass. Lay down the cloth so that it1 square meter area). Pour in “S” curves as runs at least an inch past the outer edge ofdescribed in the coating section (on steep the tape. Wet out the glass past the innersurfaces apply the epoxy with a roller cover edge and about half way across the tape.and roller tray), spreading lightly into the dry When the cure reaches the green state run aareas with a squeegee. We like the rubber single edge razor blade right down the innersqueegee for laying down cloth. Let the resin edge of the tape. Pull off the tape and presto,wet the cloth out. Don’t try to “force” it through you have a nice edge right where you cutthe weave with the squeegee. Notice how the fiberglass. If a little of the cloth lifts, pressthe cloth disappears as it wets out. it back down. 10
  12. 12. The weave of the cloth can be filled once the roller cover and a roller pan. Use justresin has reached the green state of cure, enough epoxy to wet out the cloth. Whenpreferable the same day. If this is not practical, cured finish in the usual way.sand lightly but thoroughly before recoating.Don’t try to sand the weave smooth, fill it Corners and edges often require severalwith epoxy. Apply fill coats the same as layers of cloth. Giving thought to a “glassingdiscussed in the preceding section on pattern’ will allow doubling at chines andcoating. Several coats may be necessary sheers without going through extra steps.before the weave is filled. It is possible to Corners are most easily “patched”. Cutthicken the epoxy slightly and do it in one circles of different diameters from clothcoat using a squeegee. Anti-sag Powder scraps. Wet down, dabbing at it with an(Cab-O-Sil) works best but don’t use any epoxy soaked brush. Lay down the nextfiller on surfaces that are to be clear finished. larger circle over this wetting it with more epoxy, if necessary. Continue the processWhen the weave has been filled the surface until finished. Each larger circle will fray theshould be sanded to prepare it for painting cut edges of the smaller circle under it. Thisor varnishing. Sand the epoxy, not the process is called self-feathering. Use thefiberglass. Be sure to wear a respirator or masking tape trick for the last circle and thedust mask, gloves and a disposable paper job will require little sanding to look nice.suit while sanding. If you do get the fiber-glass itch take a cool shower, it will go away Heavy structural seams are best-done usingin a few hours. biaxial tape. Biaxial means that the fibers run at 45 degrees to the way the tape comesApplying fiberglass overhead is at best a off the rolls. When run along a seam ALLdifficult, messy job. Anyone who has tried it the fibers run across the seam at 45 degrees.once has no desire to repeat the experience With regular plain woven tape half the fibersand will do everything possible to try to turn run parallel to the seam and add nothingthe boat over or at least work on a slant. If to strength.this is not possible then there are severalsuggestions for accomplishing this job. Biaxial tape is heavy at 18 or 24 ounces per square yard and it won’t be clear like lighterIf you are working on a relatively small area, tape when wet out with epoxy so don’t usewet the surface with mixed resin/hardener it for bright finished seams. Rather thanand lay a rough cut piece of cloth into the featheredge biaxial tape by sanding weresin. Surface tension will hold it into place prefer to fair the edges using an epoxy/without sagging if too much resin is not balloon mixture.used. Using a squeegee overhead is a featno one has yet mastered. Use foam rollers. In summary, fiberglassing is a three-stepOnce the epoxy has cured you finish the process:overhead area in the usual manner. 1. Seal the porous surfaces to preventGlassing large overhead areas calls for a starving the joint. Do filling and fairingdifferent technique and a helper or two. on the sealed surfaces. Sand lightly butMost successful jobs are done by rolling on thoroughly.a coating, then allowing it to cure to a tackystate. The cloth is then rolled as smoothly 2. Stick the cloth down leaving a minimumas possible onto the tacky coating. This is amount of resin in the cloth.where you’ll probably need more than one 3. Fill the weave any time after the wetperson. Get the wrinkles out as you go along; cloth has reached the “green stage” andyou won’t be able to slide them out because is stuck to the substrate.the tackiness of the coating will hold thecloth in place. Once you’ve got the clothwhere you want it press it into the tackyundercoat with a dry foam roller. When itis all smoothed down, wet it out using the 11
  13. 13. filleting putties to improve tensile strength, Using Fillers with and are listed above in descending order of Epoxy Resins tensile strength improvement.Cold Cure epoxy properly mixed is intended Paste pigments (titanium dioxide), blackfor both coating and fiberglassing. When paste (Carbon Black) and aluminum powderused “right out of the jug” the mixture is said are generally used as pigments. Addingto be “unfilled” and it is too thin to be used white paste pigment produces a white resinas a gap-filling adhesive or for fairing and coating that is useful for areas where a lightfilleting compounds. For these applications color is desired and painting is difficult.certain fillers are added. These materials Pigments aren’t meant to serve as substituteschange the flow and density characteristics for paint in areas exposed to direct sunlight.of the epoxy system. White paste pigment is useful when added to the final fill coat when fiberglassing,All powders sold for use with Cold Cure allowing this coat to serve as a cover coatepoxy products are solid materials, falling for finish painting.into four general classes: thixotropic agents,bulking agents, fibers, and pigments. There Our pigments are pure dry colorants groundis some overlapping as to function of certain into epoxy resin to produce an epoxy pastefillers. For example, plastic minifibers is both pigment. Since they are dispersed intofibrous and acts also as a thixotropic agent. epoxy resin they may be added to the resin side of our epoxy systems to produce aAnti-sag powder (Zeothix), plastic minifibers stable pigmented resin. Measure the amountand wood flour are thixotropic agents. They of the pigmented resin used to determine theturn the epoxy into a thixotropic fluid. Most amount of hardener required. Used in verypeople are not familiar with the term “thixo- small amounts these pigments are transparenttropic” though everyone is familiar with the in an epoxy and can be said to act as dyes.properties of these fluids. They flow under In larger amounts they are opaque.shear stress but do not flow once the stressis removed. Adding these agents to the Fillers change the mechanical properties ofmixed resin and hardener produces a fluid, the cured resin, however, for all practicalwhich will easily flow under the spreading purposes these changes can be ignored.stress of a putty knife. Once the stress is Thixotropic agents have the least effect sinceremoved the thickened epoxy retains shape. they are used in the smallest amounts toIn short, these powders make the epoxy produce the desired result. Bulking agentsnon-sagging, being added to restrict drainage reduce tensile strength in proportion to theand make gap filling adhesives. amount added. Some will initially increase compressive strength. With increasingPhenolic microballoons, quartz microspheres, amounts of additives, though, compressiveand wood flour are bulking agents. They strength will decrease.“bulk out” the epoxy making a lightweightputty-like mix. Although all these thicken Numerous combinations of filler materialsthe epoxy, only wood flour will make it are possible and we have not tested them all.thixotropic. Attempting to add sufficient If you have an idea that a certain combinationmicroballoon or microspheres a non-sagging might do something special for you thenfairing putty will result in one that spreads check it out. Little pieces of scrap plywoodpoorly. These materials should be used are good for this. Think up some destructivealong with a thixotropic agent. Anti-sag tests that will simulate the stresses thePowder is the best choice because it produces material will see in service. Check to seethe smoothest compound. where the failure occurs. If the wood breaks then your combination should work wellChopped glass strands, milled glass fibers, with wood, at least.and plastic minifibers are fibrous materialsthat can be incorporated into structural 12
  14. 14. This is the correct sequence for the addition wood scarf joints are made at a minimumof filler materials: 8:1 slope. Fillets increase glue surface area and are used to relieve stress concentrations1. Correctly measure and mix resin/ that build at right angle corners. Stringers, hardener for example, should have fillets where they2. Add fiber fillers, if any and mix well butt onto planking.3. Add bulking agents, if any and mix well4. Add thixotropic agent and mix well. Second, make sure that the surfaces being glued are clean, free of grease, oil, wax, and other contaminants that could act as release Epoxy Resins as agents. If the surface is coated with cured epoxy, sand before gluing and wipe the dust Structural Adhesives off. Remove paint rather than trying to glue onto a painted surface. Epoxy resins stickThe mixed viscosity of Cold Cure epoxy is well to paint although the overall bondnot high enough to make a good gap filling strength will be no better than the paint toadhesive. Thixotropic agents like Zeothix, substrate bond.Plastic Minifibers, and Wood Flour are usedto thicken the epoxy and change the flow Third, do not overclamp. Epoxy resinscharacteristics. These fillers will turn the require only contact pressure. Overclampingepoxy from translucent to opaque depend- can squeeze most of the adhesive out of theing on the type and amount used. Anti-sag glue joint and the epoxy that is left may beand Plastic Minifibers make the powder absorbed if the surface is porous, starvingepoxy whitish while Wood Flour turns it the joint. A glue-starved joint is very weak.reddish-brown. Anti-sag makes a smooth Use only enough pressure to hold the jointmaterial while epoxy thickened with Plastic immobile and keep the two surfaces inMinifibers or Wood Flour will be coarse. contact until the epoxy has set – overnight at normal temperatures. Nails, screws,Microballoons and microspheres should not clamps, rubber bands, or staples can all bebe routinely used in an adhesive formulation utilized to do this holding job. Clamp justas they reduce tensile strength. Quartz hard enough to close up the joint.Microspheres may be used as a filler/thickener for cold molding where the surface Fourth, remember that epoxy resins continuearea to be bonded is large with respect to the to cure and build strength for several daysmass. Microspheres are acceptable here after they solidify. Joints that will be underbecause of the large glue surface area immediate stress once they are unclampedinvolved and the low microsphere loading need more cure time before the clamps arelevel. removed. Overnight cures are usually sufficient for most non-stressed joints. AMaking an epoxy glue joint is quite simple. common cause of epoxy joint failures is tooFirst, properly measure and mix the resin much stress before the epoxy has reachedand hardener, then coat both mating surfaces sufficient strength. Such a case might occurwith this unfilled epoxy to wet them out. It is where a scarfed joint is unclamped and bentnot necessary to let this coat cure. Next add into place too soon.the thixotropic agent to the balance of themixed resin/hardener blend and spread this Fifth, protect any finished wood glue jointthickened resin on either of the two surfaces from weather degradation. Wood that isto be glued and close up the joint. That’s all allowed to weather will cycle through moisturethere is to it – but there are some tricks and content extremes. Wood expands as thethings to keep in mind. moisture content increases. This expansion can set up enormous stress concentrationsFirst, remember that the ultimate strength of across the glue joint due to uneven rates ofany glue joint is a function of the glue expansion on either side of the glue line.surface area. The more surface area, the These stress concentrations can exceed thestronger the joint. This is the reason that strength of any glue, including epoxy resins, 13
  15. 15. causing failure. Protecting the joint by epoxy Epoxy resins usually bond well with curedcoating all surfaces of the glued wood stops thermoset materials like polyester, vinylthe moisture cycling and prevents failure ester, and other epoxy resins as long as thebecause of weathering. This is not a problem cured surface is sanded and wax free. However,for wood glued with epoxy that will not be you should not try to bond polyester, vinylsubject to deep moisture cycling. ester, or other polymeric materials which are cured with MEKP or other peroxide catalystsCold Cure epoxy works well for use as an to cured epoxy resins.adhesive for wood-to-wood and fiberglasscloth-to-wood bonds. When we are asked if There are too many materials and combina-it can be used to bond metals and plastics tions to cover every possibility. We suggestthe general answer is that it depends on the that you model any questionable materialsmaterials involved and their intended use. that you want to bond. Glue some scraps and test them. Try accelerated aging andMetal/metal bonding success depends retest them. If they survive an hour in 70°Cupon the type of metals bonded, the surface (160°F) water they will probably last for quitepreparation, and the intended service a while. You have the ultimate responsibilitytemperature. Generally, we recommend for your own work.against making structural metal/metal bondswith epoxy resins unless they are specifically Sometimes there’s a need for clear gapformulated for that purpose. Our testing filling thickened epoxy. It’s not possible toshows that these bonds degrade over time produce such a material using any of thedue to different thermal expansion rates solid thixotropic agents previously discussed.setting up shear stress and resultant interfacial Our G-1 glue is handy for this since it isfailure. For non-structural applications the clear and thick.flexible mastic materials appear to holdbetter than the more rigid epoxies as they 5-Cure is our 1:1 “five minute” epoxy. Itemsallow for thermal expansion. glued with 5-Cure can be stressed in as little as 10 minutes. It is very handy to have in theMetal/wood bonding for non-structural shop for this reason. Builders often find thatapplications may be done successfully with “missed screw hole” when ready to lay downCold Cure epoxy providing that the metal is the fiberglass cloth. Mix a little 5-Cure, addclean and bright. Structural applications are some Wood Flour or Anti-sag and you’ve gotbest when they are mechanically fastened. an instant putty to fill the hole. 5-Cure canDon’t put stainless bolts in epoxy resin. also be used in combination with Cold CureStainless steel works only in the presence as a “spot welder” where clamping is all butof sufficient oxygen. The epoxy will deprive impossible.it of oxygen causing crevice corrosion inthe presence of an electrolyte like seawater. Coat the pieces to be bonded with thickenedStainless steel fastener failure occurs where Cold Cure epoxy except leave several golfthe bolt emerges from the epoxy resin. ball-sized bare areas. Mix some 5-Cure and apply to the bare areas. Push the pieces toBonding to metal alone such as fairings on be bonded together with enough pressurelead keels will work well with Cold Cure to cause some “ooze out”. Hold in place forepoxy so long as the lead is bright and free about five minutes until the 5-Cure hardens.of oxidation. Now the 5-Cure will hold the pieces together while the Cold Cure epoxy sets.Thermoplastic materials like vinyl, PVCor ABS generally bond poorly with epoxy Unlike our other epoxy systems 5-Cure andresins. If you need to bond any of these test 30-Cure, like all similar epoxy products, isthem yourself. You will get the best results if water resistant, not waterproof. It is fine foryou first sand the plastic with coarse paper. intermittent water contact but should notEpoxy will not bond to polyethylene, be constantly immersed.polypropylene, or Teflon. It bonds wellto neoprene and polyurethane rubbers. 14
  16. 16. than sanding the whole fillet down to a Filleting, Fairing, and common level. Blow or brush off the sanding Molding with Epoxy Resins dust (wear a dust mask!). Make up some more filleting compound and use a broadCold Cure epoxy is mixed with phenolic putty knife to fill the low spots resting themicroballoons (purple), quartz microspheres blade against the fillet parallel to the long(white), or wood flour (brown) to make putty- axis of the filet. Allow the putty to cure andlike material that is used for making cosmetic do a final sanding. That’s it! Perfect fillets inor structural filleting, fairing, or molding two easy steps with little sanding.compounds. Rather than supply thesecompounds in a premixed form, we supply Before microballoons are painted theythe raw materials so that builders are should be sealed with epoxy or else theallowed the versatility of creating customized paint goes into the tiny hollows in thecompounds to fit a specific need. broken balloons and the finish will appear ragged. Brush or roll on a coat of epoxy onFilleting is the process of adding an epoxy the sanded balloons, allow to cure and sandputty to concave angled corners for cosmetic lightly before painting.and structural reasons. Cosmetic fillets aregenerally “low density” being made by the Structural fillets increase the glue jointaddition of microballoons which “bulk out” surface area relieving stress concentrationthe epoxy. Structural fillets are “high density” zones that occur at angled corners. They areand are thickened with anti-sag mini-fibers usually made at the same time that the pieceor wood flour. These fillets sometimes creating the corner is attached. For example,contain glass fiber. Thixotropic agents make when sheet plywood is glued onto a stringerthe mix non-sagging when sufficient the excess glue that oozes out can be usedamounts are used. Microballoons and to form a fillet. A gloved finger makes amicrospheres do thicken the epoxy, but good filleting tool, as these fillets don’twhen used in proper loadings do not need to be large.prevent sagging, and need the addition ofa thixotropic agent. Large structural fillets are generally made in a separate operation in a manner similar toCosmetic fillets are applied by putting an making cosmetic fillets. If they aren’t goingexcess of material along the length of the to show there really is no need to make themcorner with a putty knife or caulking tube. pretty. The addition of either milled glassBe careful not to force big air bubbles into fibers or chopped glass strands improves thethe fillet when putting the putty in the tensile strength of structural fillets.corner. A rounded tool is used to shape theputty by drawing it along the fillet. The sides Fillets in stitch-and-glue construction usuallyof the tool should touch both sides of the are fiberglassed. The easiest way to do this iscorner and the tool radius is determined to fiberglass the fillet when it is in a semi-stiffby how rounded the finished fillet will be. state so that it can still be pushed around withAlmost any material can be used to make an epoxy-saturated brush. This saves havinga fillet tool. Plywood paddles work well, to sand the fillet after it is cured.are easy to make and are inexpensive.The excess putty will be forced out on Fairing is the operation of filling the loweither side of the tool where it is scraped spots to the level of the high spots, eliminatingoff with a putty knife. waviness and hollows. The compound used is identical to that of the cosmetic fillet andOnce the fillet is cured it may be sanded. the operation is similar except that large flatA round edged sanding block with coarse areas are involved. Large drywall broad(50 to 60 grit) paper works best. Knock off knives, stiff boards with tapered edgedthe high spots with the sandpaper and then squeegees, and similar tools are useful forcome back and fill in the low spots with an fairing. Once the putty has cured it is sandedadditional batch of putty. This is much easier with large blocks to a level fair with the surrounding area. On very large areas low 15
  17. 17. spots may appear during sanding that will months of intense tropical sunlight onneed a second fairing. After final sanding the horizontal surfaces. Total breakdown willfairing compound should be sealed with occur about 15 months under these sameepoxy prior to painting. conditions.A slick way to fair a large area and avoid a Bright finished boats should be finished withlot of tedious sanding is to use a serrated a clear coating that contains a UV inhibitor.trowel like the metal one floor tilers use to This inhibitor is sacrificial so the coatingspread mastic. Apply the fairing putty using must be periodically renewed if the epoxythis tool leaving a series of parallel ridges is to be protected. When the clear coatingthat stand proud of the surface. Allow the starts to look dull it’s time to refinish. Oldputty to cure, then sand the area. Notice that coatings are removed by sanding or areall you are sanding is the tops of the ridges – chemically stripped with strong solvents.about one fourth of the total surface is being Test patch an inconspicuous area to makefaired. Sanding dust falls into the valleys. sure that the solvent used does not attackOnce the ridge tops are fair, the area is the epoxy base. Solvents and removerscleaned of sanding dust and the valleys are containing methylene chloride will etchfilled with fairing compound using a broad epoxy surfaces. Don’t use these. Be sureknife with a straight edge. Only a light to observe the usual precautions whensanding is then required for final fairing working with these solvents.following cure. Seal with epoxy beforepainting. Opaque paints do not allow the passage of UV light, offering the best protection of the epoxy coating. A primer coat prior to painting Painting and Finishing over Industrial Formulators epoxy with these paints is quite helpful for several reasons.Over the years nearly half of the technicalservice questions we’re asked involve Besides bottom paint, three broad classes ofpainting and varnishing. More than anything coatings are commonly used as boat paints.else this has been the area that has caused These are the “one part” alkyd and modifiedmost people trouble. We have solved these alkyd enamels commonly called “oil baseproblems by developing our own painting paints”, the “two part” epoxy and the two partsystem for epoxy resin surfaces – more on linear polyurethane (LPU) paints. Since allthis later. epoxy based materials eventually chalk in sunlight be careful to consider exposureIndustrial Formulators epoxy surfaces may when using the two-part epoxy paints forbe coated either with opaque paints or exterior finish coats. Two part epoxy primersfinished with clear varnishes. The epoxy are recommended as high build sandingsurface accepts finishes like any other non- base primers for LPU paints.porous surface except that it is chemicallyactive to certain materials because of Be sure that you are getting what you expectunreacted amines on the surface and when purchasing a marine paint. Paints soldthroughout the epoxy matrix. in marine stores today are a triumph of marketing over technology. Remember theAll outside epoxy surfaces exposed to adage: “The big print giveth while the smallsunlight must be protected from degradation print taketh away.” It is not uncommon to seeby ultraviolet (UV) light. This is the invisible the pretty face of a paint can staring back atshort wave length portion of sunlight that you screaming “Buy me! I am a one partcauses sunburn. The long-term effect of UV polyurethane”. Yet, when you read the back ofon unprotected epoxy is a dulling of the the can you find that the ingredients state thatclear film, followed by chalking and, finally, it contains polyurethane safflower alkyd resinfilm cracking and delamination. The initial or some other modified alkyd. If it says alkydeffects of UV degradation on Industrial anywhere on the can then it is an alkyd NOTFormulators epoxy start after about six a polyurethane. True polyurethanes often 16
  18. 18. referred to as LPU paints are two parts and “Test patches” are advisable prior to paint-cost about two to three times what an alkyd ing or varnishing over an epoxy coating.costs. If the ingredients are not specified on These test patches will give you a feel forthe can, then ask for a MSDS on the paint. how the various coating materials handle and point out any possible incompatibilityAlkyd enamels and related one part solvent- problems to their becoming a disaster allbased paints and varnishes are easy to work over your boat.with but may not properly dry on epoxyresins. They may be brushed, rolled or To do a test patch, coat a small area with thesprayed and dry to a glossy film that is easy painting system selected to make sure thatto refinish. Their main drawback as a finish each paint layer dries properly and adheresis that they are softer than LPU paints and well to its substrate. One reason for doingchalk slowly over a period of time. this is that epoxy resins, despite sanding and long cure time remain chemically active toLPU paints dry very hard with excellent certain components of alkyd paint andgloss, are not degraded by sunlight and varnish systems. Generally, epoxy primerswear very well. Their main drawback is that and LPU paints are compatible with epoxythey require immaculate surface preparation. resin coatings and may even chemicallyThe solvent based LPU paints contain some bond. However, some of the alkyd enamelsvery hazardous materials and are difficult to and other one part paints and varnishes mayapply. They can turn dull when curing if the not properly dry on epoxy resin coatings.humidity is too high. Our experience is that The free unreacted amine in the epoxy resinthe application of solvent based LPU paints coating interferes with the action of theis beyond the skill of most amateur mettallic driers in some of these paints.boatbuilders. If this happens the paint may surface dry but remain soft and tacky next to the epoxyBecause of the ultra high gloss and thin resin surface.film of LPU paints any imperfection in thesubstrate will show in the finished coating. A similar chemical phenomenon occursThus, the tendency of the alkyd paints to between the amines in epoxy hardeners anddull to a semi-gloss finish over time can hide the peroxide catalyst used in polyester andsome of the flaws that might otherwise mar vinyl ester resins and primers. The aminesan LPU finish. However, if the boat is perfect inhibit the action of the peroxide catalystand you are willing to spend the time and preventing cure at the interface. For thiscare required to use LPU paints, she’ll even reason, it is not possible to “gel coat” curedbe more beautiful. epoxy without specialty barrier coats and it is very risky to use peroxide cured polymersUse any color you want so long as it is light. directly over cured epoxy resins. Besides,If you paint with a dark color and the boat is gel coats don’t look all that good whenin the summer sun you are going to experi- applied to a male form. Their best use isence a number of problems especially if it is against a polished female mold.a wood boat. First, you’ll get “print through”.This is the telegraphing of the cloth weave Be sure to follow the paint manufacturer’spattern to the glossy painted surface. Second, instructions when doing the test patch. Withyou’ll see what appears to be shrinkage of the exception of the high build two partthe epoxy resin (microballoon putty over epoxy primers, all finish paint systemsscrew holes, for example). This is caused by should be applied thinly. Thick coats willthe expansion and contraction of the wood not dry properly and may take weeks tofiber due to changing moisture content “through dry”. Temperature and humidityrapidly aggravated by excess heat soaked play an important role in the speed of alkydup by your darkly painted boat. Finally, the paint drying. The higher the temperatureuseful life of the boat will be shorter. and lower the humidity, the faster drying. 17
  19. 19. You can gauge drying by digging yourfingernail into your test patch and scratching. TroubleshootingIf the paint film is still soft below its surfacethen it has not finished drying. A dry film is Following are questions we are commonlyhard all the way through. A simple test asked when something goes wrong. Wecalled the cross hatch adhesion test will show hope that you will read them because if youhow the new layer bonds to he substrates. Do have a problem the answer may appearthis test only on paint that has dried thoroughly. below. If it doesn’t then call us on ourTo do this test, take an industrial razor blade technical line and we’ll go over it with you.and score the surface with a set of 8 parallellines about an eighth of an inch apart. Score Problem: The epoxy has turned hazy and hasa similar set at 90° degrees from and crossing white material in the bottom of the jug.the first set. The finished lines should look Cause and Solution: The epoxy is crystallizinglike a giant tic tac toe grid. Take some tan due to storage at too low a temperature. Heatmasking tape and press the sticky side into resin to 60°C until crystallization clears. Youthe grid leaving a tail. Press the tape with the can do this by placing the material (enclosedback of your fingernail. Grab the tail and jerk in its original container) in a hot water baththe tape off the grid. Examine both the tape or in a black plastic bag in the sun.and the grid for paint adhesion failures.Except for the grid lines on the tape, no paintshould come off on the tape. If it does then Problem: The epoxy isn’t curing.you have an adhesion problem and it WILL Cause and Solution: It was mixed at the wrongshow up on your boat most likely in the form ratio. Resin was mixed with resin or vice versa.of paint blisters. Resand with a coarser grit Remove the uncured material thoroughly byor better, select a different substrate/top coat scraping and solvent washing. Mix at propercombination and test it. ratio and reapply.Once you are satisfied that there are nosystem compatibility or adhesion problems Problem: The epoxy keeps going off in the pot.then you can paint your boat with confidence. Cause and Solution: The batch is too big or leftBy this time you are probably wondering too long in the pot. The hardener is too fast forwhy we don’t just give you a list of what the conditions. Use a smaller batch and get itpaint brands you can use. We would if we out of the pot sooner. Change hardeners.could but because paint makers are free tomodify their formulations without notifying Problem: The epoxy is still gummy.Industrial Formulators we will not recom-mend a specific brand of paint. The batch Cause and Solution: The ratio was wrong. It waswe test might have changed by the time inadequately mixed. Not enough time hasinformation about our results gets to you. elapsed at the curing temperature. Make sureIt is not possible for us to keep up with all that the gumminess is not just the aminethe different brands and lot numbers. blush. Wait and see if the cure proceeds. Apply some heat if possible. If it is still gummy then remove the uncured material thoroughly by scraping and solvent washing. Mix at proper ratio and reapply. 18
  20. 20. 3824 William St. Burnaby, BC Canada, V5C 3H9Technical Support: (604) 294-5723 FAX: (604) 294-8052 Orders Only: 1-800-778-0833

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