The Latest

Epoxy and Finishing

On November 28, 2012, in Shop Talk: Tips and Techniques, by Gayle Brantuk

As a general rule, we advise against spray application of paint systems unless you’re already an expert and have the proper facilities to assure sound, safe results. With a good paint system, properly applied, excellent results are possible by the amateur without using spraying methods (rollers and brushes work well with many systems).

Before doing any finish work or applying finishes, allow the last coat of epoxy to cure 5 to 7 days at 70 degrees F, longer at colder temperatures. Wipe down the hull with a water/ammonia dampened rag or sponge. This will eliminate the greasy feeling amine blush to make final finish sanding easier and minimize clogging of the abrasive.

lf you have been careful in your application of resin with all coats, making sure each is evenly applied, and have taken care to prevent runs and sags, and to correct mistakes along the way, the finishing process should be relatively easy. Final finish work will vary depending on the quality of surface which is desired, whether the surface will be naturally finished or painted, and whether or not a sanding undercoat will be used.

Final finish sanding is usually done with either an orbital sander or hand sanding block. lf you wish to use a disc sander, equip it with one of the foam backing disc pads which will minimize gouges. lf you have not used a disc sander, some practice may be in order since these can easily damage a surface. The rpm of the disc sander should be kept relatively low (around 2000 rpm) since it is possible to scorch the resin surface if rpm’s are too high.

Start out sanding with a 60 to 80 grit open coat paper, advancing to a 120 to 180 grit. For many builders, this will yield good enough results for painting, but for a high-gloss natural finish, work up through finer grits as required, ending off with a 220 to 280 or even finer grit wet-or-dry paper using wet sanding techniques. Be careful not to remove too much resin by sanding, and if it looks as though too much sanding will have to be done, it may be better to apply more coats of POXY-SHIELD®.

Note that POXY-SHIELD® will not in itself provide a perfect “bar top” finish, even when flow coating. Although the epoxy has high gloss properties, it is not a final finish. An ultimate final high-gloss brightwork finish is best achieved through finish sanding and coating with varnish or comparable clear coating products, and such is required for all exterior use for U-V protection.

lf using varnish, apply at least two coats (more is usually better) of a U-V stabilized varnish or clear polyurethane product. lf your surfaces are to be naturally finished, it is preferred to use only Fast hardener for all coats for a faster cure and better long-term clarity. lf the resin cures more slowly, such as with the use of the Slow hardeners, a potential exists for clouding of the clear coating in the presence of moisture.


Epoxy resin products can be messy and get on surfaces where they are not wanted. They should be removed before they cure to avoid having to grind them away later. This is especially important when gluing around interior areas or on surfaces where visual appearance will be important. While the resin should be cleaned up before it cures, there is no particular rush to remove immediately as it exudes from a joint. In fact, as it stiffens up a bit, removal is actually easier since there won’t be as great a tendency to spread it around while it is still fluid, especially with POXY-SHIELD® due to its thin viscosity. However, don’t wait too long or the resin will cure hard. Nothing can remove the resin at this point other than sanding (an oscillating tool works great too).

Excess resin can be removed with thin sticks of wood, putty knives, or similar tools. Don’t let the uncured epoxy fall to the ground or floor where it will stick to anything and everything or get tracked around; scrape it off into a container. Then wipe surfaces that are to be cleaned using a lint-free rag soaked with a proper solvent. Don’t use tack cloths as they will add wax to the surface.

DENATURED ALCOHOL is the best and probably the safest solvent from a bodily contact standpoint (although it is flammable). Ordinary mineral spirits (paint thinner) is also relatively safe. Other solvents are more hazardous, from a vapor inhalation and/or flammability standpoint, as well as from long-term health affects.

ACETONE is a very effective solvent but has a relatively high evaporation rate, making it necessary to keep the container closed at all times when not in use for safety and economy. The main problem with acetone is that it is highly flammable. Any wood boatbuilding situation offers the potential of a fire hazard, and therefore fire safety is always important.

LAQUER THINNERS are a generic group of solvents which function similarly to acetone, however, there are different formulations. Fumes are also easily detectable in most, but they are not quite as volatile as acetone, yet still considered highly flammable.

TOLUENE, a common constituent of lacquer thinners, is not quite as flammable as acetone nor as volatile, but can reach anesthetic affects at much lower levels. A 50/50 mix of toluene and acetone is sometimes used as a solvent to moderate the qualities of each.

Just about all solvents are dangerous products from one or more respects, and costly. Skin contact should be avoided, especially when working around epoxy products. Most of these products tend to open the skin pores and remove protective skin oils, driving both the solvents and the resin more deeply into the skin and perhaps ultimately into the system of the user. The results are a much greater risk of skin reactions of greater severity.

For personal clean-up of uncured resin from skin, ordinary water and soaps or detergents (including ammonia), or denatured alcohol can be used. However, we prefer the use of waterless hand cleaner products which are specifically intended for use with resin products. These usually have added protective oils that keep the resin from being absorbed by the skin and don’t tend to dry the skin. Of course, personal clean-up is much easier if barrier cream has been applied-and protective clothing and gloves worn.

Again it should be emphasized that neither POXY-SHIELD® or POXY-GRIP® products should be thinned with solvents or thinners. This will distort and adversely affect the properties of the resin, perhaps to the point where they simply will not work.

Epoxy Troubleshooting & Tips:

“Help! There’s bubbles in my resin!”

There are two common causes of bubbles in resin. One, air escaping from newly coated wood. This usually only happens on the first coat, but may occur on subsequent coats if the wood is not sealed with the previous coat. Sometimes the bubbling is minimal, sometimes there are lots of bubbles. Why? I’ve heard… differences in temperature between wood and ambient air temperature, between wood and resin temperature, when the wood is warm… so maybe it has something to do with temperature. Anyway, what do you do about it? Lightly sand and recoat. If you are going to fiberglass, lightly sand and fiberglass.

Two. The other cause produces bubbles that look more like foam, that make the resin look milky, and can occur any time you apply resin. What causes it? You do. When you use a roller to apply resin (as we do) you may sometimes roll the roller quickly back and forth in order to wet out a particularly stubborn patch of bare wood or cloth. What you are doing is “whipping” the resin. To correct the problem, drag the surface lightly with a brush. The bubbles may migrate out of the resin on their own, if the resin doesn’t set up too fast, but if the surface is ultimately going to be clear, it’s best to brush them out.

How to Increase Working Time

The moment epoxy resin is activated, the chemical action creates heat and heat shortens working time. To lengthen working time when working with larger quantities, get the activated epoxy into a container with a lot of surface area. Mix small batches and have the ingredients for the next batch measured and ready to mix when needed. At higher ambient temperatures, cool the resin components or store them in a cool place. Do not work in the sun. At approximately 70 degrees in a large surface area container, we expect to have 20 minutes working time; more if the mixture is removed from the container quickly.


Your Thoughts?

One Response to Epoxy and Finishing

  1. Tom Weyand says:

    Several folks on a multihull boatbuilders list reccomended vinegar as a solvent for uncured epoxy.

    I haven’t had reason to test but if it works it would be immensely better than some of the traditional solvents listed.


Leave a Reply

Your email address will not be published. Required fields are marked *