Thinning

[420TEE]

As the beard gets longer the memory gets shorter. What besides xylene is used to thin finishing epoxy? My local hobby, hardware store (Wally's Joint) doesn't carry xylene.

[patmat2350]

Lacquer thinner or denatured alcohol (but not the stuff from the drug store, too much water).

West Systems says that thinning degrades epoxy's properties (strength and long term water resistance). It just isn't necessary to thin it to get good coverage and penetration.
But if you want that last coat to flow, they then recommend HEAT over thinning... preferably warm the substrate, but you can also warm the applied epoxy VERY CAREFULLY with a heat gun, or in the back of your truck camper on a sunny day!

Pat

[yacht boy]

From years of experience in the marine industry I would agree. Best not to thin.
Also try to use RADIANT heat, not a hot air gun or hair dryer, or even a fan heater.
If you have no alternative then use the blown air to heat a sheet of metal or the floor underneath the work piece.

[bill g]

If you absolutly have to thin the epoxy, use acetone. It works, BUT slows the cure time considerably

[420TEE]

Interesting comments considering I was chastised for not thinning the epoxy in my comments under the Lyman build thread.

[scififlyer]

In his "Vacuum Bagging" DVD Phil Barnes keeps his epoxies in a foam-slab box with an oil filled heater set for 100 degrees. Very good results, his epoxy mixes well and spreads with a paint roller easily. He also cures his layups in these heated boxes made from insulating styrofoam in 4'x8' slabs.

[boat_builder]

I've used the Lacquer thinner method and it worked out ok for me. It did make curing take longer but it got the results that I was looking for. I mixed in the thinner as 8:1 ratio (8-parts epoxy 1-part thinner). It thinned the epoxy pretty good but hasn't seemed to have any real serious negative effects. I liked doing it this way because it really cut down on sanding because there were aloooot less brush marks left after curing. I never could get acetone to mix with the epoxy that I use, don't know why but it wouldn't, just made a mess. I didn't have any luck with denatured alcohol either, once again, not sure why. Both acetone and denatured alcohol were in pure form bought in gallons from a paint shop.

I have also used the heat method which worked real well also. Heat may be a better way of doing it because it wont effect the quality of the epoxy in strength, longivity, ect.. To heat my epoxy I always just filled up the kitchen sink with hot water and then put the epoxy containers in the hot water and let them sit for about 15-20 minutes before mixing. I have also used a heat gun after the epoxy was applied but learned very quick to keep it a good distance back from the work so it doesn't make the epoxy bubble. A hair dryer has worked best for me in that method because it doesn't get as hot. :)

Some of the other members here may have better advice for you on this than I because alot of them have been doing this longer and have more experience. I'm not trying to contradict any advice of the others, these are just the methods that I have used and experimented with that have worked pretty well for me even if they may not be considered the best methods. :) :) :) Good luck to you!!! :)

[frankg]

:) 420TEE- In all the years of building models I have always used XYLENE to thin my epoxy finishing resin. The reasons are as follows, and I have never had a problem with strength or finish when using it. First when using the resin as a penetrating resin I thin the mixture 40/60 or the consistency of water to penetrate right thru balsa wood hulls and seal end grain of light ply wood. Second when using the resin for build up for finish I put just the slightest touch of XYLENE to the epoxy mix to eliminate any bubbling that occurs when brushing on the epoxy. The reason this happens is that with the addition of the XYLENE the surface tension of the epoxy is broken to allow the air bubbles to escape more easily. This will give a bubble free coat of resin that you are looking for when building up for finish especially on a mahogany planked hull. I find for my own preference that XYLENE is far superior to ALCOHOL or LACQUER thinners. By the way I have been using the Z-POXY finishing resin made by PACER which is available at any good hobby shop or from M.A.C.K. Products. www.mackproductsrc.com By the way XYLENE can be purchased at any Home Depot or LOWES home center. I also buy 99% of the spray paints I use on my model there. :)

[time4420]

I had my own lengthy post going then I just googled it...



Thinning West System Epoxy


by Brian Knight

This article appeared in the Fall 1999 issue of Epoxyworks, published by Gougeon Brothers, manufacturers of the West System epoxies. Our thanks to Gougeon for permission to publish this in the December 1999 Falco Builders Letter. For more information on West System epoxies, please visit the Gougeon Brothers website.


A question frequently posed to our technical staff is "can I thin West System epoxy so it will flow or penetrate better?" The answer to that question is "yes, but not without consequences." Many of the advantages of thinning epoxy are offset by disadvantages in other areas of epoxy performance.

Thinning epoxy means lowering its viscosity. Low viscosity epoxy flows better, is easier to roll or brush, saturates fiberglass fabric quickly, and penetrates more deeply and more easily into porous surfaces like partially rotted wood. There are two methods of temporarily thinning epoxy. One is to heat the mixture and the other is to add solvent to the mix. The goal of both methods is to reduce the epoxy's viscosity. This article explains what happens to West System epoxy when it is thinned either by heating the components or adding solvent to the mixture.

Through knowledge gained from our comprehensive test programs and from 30 years of practical experience, we have learned that epoxy formulation is a balancing act. When one characteristic is altered-e.g. changing handling attributes by adding a volatile solvent-other characteristics like moisture resistance and strength are also changed. Our chemists formulate a well balanced, versatile epoxy that provides excellent structural strength and moisture resistance. If you elect to modify it, you become an epoxy formulator and need to understand the effects of your changes. Armed with the information in this article, you can decide if thinning epoxy is worth the tradeoff in performance.

Is thinning necessary?
There is a perception that epoxy needs to penetrate deeply into wood to be effective. Sometimes this is true, but most of the time it is not. Some common misconceptions are that deep penetration of epoxy 1) makes rotted wood as strong as new, 2) increases adhesion, and 3) makes wood more waterproof. The following is a brief discussion of these points.

1) Rotted wood impregnated with epoxy does not make the damaged wood as good as new. Deep penetration of epoxy into rotted wood will make the wood hard but it will not restore its original strength. This is not important if the rotted material is non-load bearing. A rotted door threshold does not need to be strong, just hard. However, when the wood fiber is damaged, wood loses its ability to carry loads and unless the fiber is replaced, it will not regain its full strength. A rotted deck beam or sailboat mast needs more than epoxy consolidation to return the wood to its original load carrying capacity.

2) Adhesion in all but the highest density wood is not enhanced by deep penetration of the glue into the wood. Research performed at the Forest Products Laboratory showed that adhesion to birch was increased slightly by using thinned epoxy. In lower density wood species like Sitka spruce or Douglas fir, the weak link is the cross grain strength of the wood. It does not matter if the epoxy penetrates l/4" into the wood or 0.005". The strength of the wood, the amount of surface area and the adhesive ability of the glue determine the strength of a glue joint. Most types of wood glue do not penetrate deeply, yet, if used properly, they can exceed the grain strength. Epoxy is no exception.

3) Water resistance of a piece of wood is not enhanced by deep penetration. Wrapping wood in plastic makes a pretty good waterproof seal without any penetration at all. Likewise, an epoxy coating on the surface is more water-resistant than a thinned epoxy coating that has penetrated deeply into the wood because, in most instances, the epoxy thinned with solvent is porous.


Figure1. MEE of various combinations of thinned and unthinned epoxy at six weeks exposure to 100% humidity.

The USDA Forest Products Laboratory developed the Moisture Exclusion Effectiveness (MEE) test. It is a measure of how much moisture is absorbed by wood when it is continuously exposed to 100% humidity. Higher numbers mean the wood has absorbed more moisture while lower numbers indicate less moisture is absorbed. You can see that epoxy with solvent added is not nearly as moisture resistant as un-thinned epoxy (Figure 1). However, if you need an epoxy coated surface that is less of a vapor barrier, thinning West System epoxy with solvent is a valid way to achieve this.

Thinning epoxy with heat
Heating the resin/hardener components and then mixing them together results in a thinned epoxy mixture that, when cured, retains all the characteristics of epoxy cured at room temperature. The viscosity of epoxy is very sensitive to changes in temperature, and warming the components (resin and hardener) and/or the substrate substantially lowers its viscosity (Figure 2).


Figure 2. Viscosity of 105 resin vs temperature. Resin viscosity is reduced as the temperature is raised.

With wood, the best method of thinning epoxy with heat is to warm the wood and have the resin and hardener at room temperature. Mix the components and apply the mixture to the warm wood surface. Remove the heat source just before the epoxy is applied. When the epoxy mixture comes in contact with the warm wood, it gets warm and its viscosity becomes lower. As the temperature of the wood falls, the thin epoxy is drawn in deeply before it begins to gel. By heating the substrate instead of the components, you get the best of both worlds-low viscosity epoxy on the work surface and longer working time in the mixing pot.

Potential Problems
Thinning epoxy with heat can create problems, however. Warm epoxy cures much more quickly than you may be accustomed to. Have things organized before you mix the resin and hardener and move quickly. Use one of the slower hardeners-206, 207, or 209-to increase the working time.

How warm is warm? You should be able to comfortably touch the substrate or the component containers when they are appropriately warmed-about 115°F maximum. Excessive heat will cause the epoxy to harden too fast, especially in thick applications. Very rapid cure will overheat the epoxy. If smoke rises from the curing epoxy, it is likely the epoxy is damaged and should be replaced.

Thinning epoxy with solvent
Adding solvent is a quick, simple method of thinning epoxy, but unlike using heat to thin it, the strength and moisture resistance of the cured epoxy are drastically affected. Below are some of the effects adding solvent has on West System epoxy. While there are a large number of chemicals available to thin epoxy, we selected acetone, lacquer thinner and denatured alcohol for this discussion because they are commonly available and do a good job of reducing viscosity. Additionally, these solvents evaporate quickly and are less likely to be trapped in the cured epoxy-an important characteristic. For a variety of reasons, fast evaporating lacquer thinner appears to be more appropriate for thinning purposes than acetone or alcohol.


Figure 3. Viscosity of 105/206 epoxy vs percent of solvent added.

· Adding a small amount of one of these solvents has a significant effect on the viscosity of the epoxy. For example, adding 5% lacquer thinner makes about a 60% reduction in viscosity (Figure 3).


Figure 4. Compressive strength of 105/205 epoxy vs percent of solvent added.

· Adding 5% lacquer thinner to epoxy reduces the epoxy's compressive strength by 35%-a big hit in the mechanical properties of West System epoxy (Figure 4). The addition of more than 5% solvent results in an excessively flexible cured-material. Thinning epoxy with solvent causes enough loss of strength that we (and most other reputable epoxy formulators) cannot recommend using it as a structural adhesive.

· Adding a volatile solvent extends the pot life and cure time of epoxy and jeopardizes the reliability and predictability of cure. Additionally, with slow rate of cure, it takes longer before work can be sanded.

· Adding volatile solvent may cause shrinkage of the cured epoxy. Applying thinned epoxy in large, confined areas (like consolidating a large pocket of rotted wood) is likely to trap some of the solvent. In thick applications, the epoxy cures very quickly and not all of the solvent has time to evaporate before the epoxy hardens. Over time, the solvent works its way out and as this happens, the cured epoxy shrinks and in many instances cracks.

Shrinkage also causes print-through. You may have a surface sanded smooth only to have the resin shrink. This shrinkage often reveals the texture of the substrate. Shrinkage can continue to be a problem until all the trapped solvent works its way out of the cured epoxy.

· Adding solvents, especially acetone, alters the color of the cured epoxy. While the effects are not immediate, adding acetone to epoxy causes the color to change from slightly amber to very dark amber.

· Adding solvent results in a temporary reduction in viscosity. Volatile solvents evaporate quickly as they are agitated during brushing or rolling, causing the viscosity to continually change as time passes.

· Adding solvent to epoxy may damage the substrate. Many materials (Styrofoam for example) are not attacked by epoxy but may be attacked by the solvent used to thin the epoxy. Be certain to test the substrate with the solvent before using it to thin the epoxy.

· Adding volatile solvent to West System epoxy has some adverse health and safety effects. West System epoxy components are nonflammable but the chance of fire or explosion goes up in proportion to the amount of solvent you add. Also, the vapors of many volatile solvents are hazardous to your health and proper ventilation is mandatory to prevent inhaling harmful quantities of them.

· Adding volatile solvent to epoxy which is then applied as a coating may cause problems with various regulatory agencies. If your business is inspected for air quality, adding volatile solvents to West System epoxy may make your business noncompliant.

· Adding solvent to epoxy to enhance fiberglass wet-out will result in more "drain out" of the resin on a vertical surface. The fabric will wet-out quickly but it may become resin starved when too much epoxy runs out of the fabric.

Does thinning epoxy make sense? In some situations, thinning is appropriate. In others, it is not. We feel that in most circumstances using heat to thin epoxy is preferred to using solvents. As long as the epoxy does not overheat during cure, the full physical characteristics of the cured epoxy remain. Adding solvent is a quick, simple method of thinning epoxy, but the strength and moisture resistance of the cured epoxy are signiflcantly reduced.

We will continue to research this subject and publish our findings in Epoxyworks.

[RC-Archer]

I'm currently restoring an old kayak and I needed some penetrating epoxy to restore and preserve some of the old plywood. Old plywood tends to start delaminating but fortunately for me I just had some minor surface delaminations that were easy to sand away.

Anyway, according to current controversial practices preached by the aficionados of the Wooden Boat forum, the proper way to treat the old plywood is to use CPES (Clear Penetrating Epoxy System). I agree. I've used it and it works very well in sealing the wood altho this epoxy has NO mechanical strength. BUT the one thing I HATE about CPES is that it is 70% solvent. The fumes alone would make your Aunt Gertrude's hair fall flat two blocks away.

After doing a lot of research, I've settled for System 3 Clear Coat. It is a penetrating epoxy but unlike other penetrating epoxies, Clear Coat is a very low viscosity solution that is 100% epoxy. Also because Clear Coat is 100% epoxy, it will soak into the wood and bond with 100% of it's mechanical strength.

So what I'm saying here is, if you need a particular type of epoxy, get the right epoxy for the job and try not to spoil the soup by changing the recipe.

[frankg]

:) RC-ARCHER- I understand whole heartedly with what you have stated and agree with the findings of the chemist talking about the west system of epoxies. But if you look at different manufactures of epoxies such as MAS or PACER they have different findings and formulas for their products. I do not dispute your findings , but I stated what worked for me, and I stand by what I said. We were talking about epoxy in terms of a modeling use, and the cost and availability of epoxy from the local hobby shop were the customer already shops. West system is a very good product but I can get pricey for use on a model. :)