The Epoxy Test

Trying to decide on the right marine epoxy for your clear coating project is not an easy task. It is especially hard when you have invested money and hundreds of hours in your wooden shell. You cannot afford to make a mistake. My hope is that this test shows how clear coating epoxies behave with or without varnish and most of all, how much care needs to be taken to protect our craft from sun damage.

Wanting to satisfy my own curiosity as well as to find the best epoxy coating for my kayaks, I am currently testing six popular epoxy types side by side to see how they compare over time while exposed to the elements – freezing, rain, sun, heat.

Click for true size version (large file)

All in all, epoxy is an amazing substance. A combination of a liquid epoxy resin and hardener creates a chemically inert plastic that can be cast to any shape, used as a filler, glue, or coating of a wide range of mechanical properties. Most important of all, it is a superb bonding agent for high tensile strength fibers and other materials.

There is a weak spot, however. Despite advances in chemistry, epoxy has one big drawback. When exposed to UV (ultraviolet) radiation such as full sun, sooner or later it discolors, turns very brittle, and eventually disintegrates. Adding pigments helps but this is no consolation if you want a clear coated fiberglass over your mahogany deck on a sailboat or a wooden kayak or canoe. A varnish or other coat with UV absorbing additives is the only solution.

Objectives and questions are listed in a decreasing order of importance.My findings and opinions about these epoxies are on theTest Resultspage.

(varnished or unvarnished) over a long period of time ( at least one year ). Can clear coated canoes and kayaks be exposed without protection over a long period without damage?

If light is completely excluded, will heat and freezing affect the coat? Can kayaks overwinter outside?

does the epoxy wet-out the 4.oz fiberglass? (dense 40×40 weave)

How quickly does the epoxy set and its

Blushing and haze when exposed to humidity and water.

A panel (5 9 x 14) simulating a deck of a wood strip kayak was coated with six types of epoxy formulations. Roughly two fifths of the panel was varnished and three fifths remained raw, unsanded epoxy. Part of the varnished as well as the unvarnished surface was covered with a 5 band of light-proof material to exclude all light. The panel is exposed to 100% unshaded south direction for the largest sun damage. It was taken outside on March 1, 2000.

1/4 wood strip bead & cove core, filled staple holes, sanded and covered by 4oz. fiberglass. Three layers of each epoxy type cover the fabric. Four thick coats of 2015 z*spar varnish cover the varnished section. Varnish coats were sanded bettween coats with 320 grit wet-dry sandpaper.

West System 105 resin and 206 hardener

West System 105 resin and 207 special coating hardener

System Three resin and medium hardener

East System 1032 resin and 834 slow hardener

All epoxies were fresh and used according to instructions. All were applied in the same environment and under the same conditions in a dry, heated workshop at 683F. The samples cured for three weeks before four coats of varnish were applied on four consecutive days (one coat each day). Note that the surface is just coated but not sanded. This is intentional to reveal blushing and the overall quality (clarity) of the free cured epoxy.

The picture below shows the panel after varnishing. There is no large difference in the clarity of the coats at this point (especially the varnished section at the bottom). Click on each section to see the detailed view. This is where the difference in the epoxies really starts to show. Coincidentally, this should represent the color of the new deck. With time the wood will darken. This darkening should be quite noticable when the light blocking plastic is removed during periodic checks.

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