flex deck case study

by: Paul Oman

Progressive Epoxy Polymers, Inc,

The cockpit floor of my 30 year old 15 ft sailboat needed resurfacing. The surface is actually the bottom (hull) of the fiberglass boat and is where the boat sits on its trailer supports. The existing fake wood patterned original surface was faded, chipped and contained many hairline gel coat fractures. The area consists of a rectangle with a centerboard trunk projecting down the middle of the forward 1/3 of the rectangle. Total surface area was about 17 square feet.

1) After standard cleaning of the surface and taping (masking) the edges a layer of 621 epoxy paint was brush applied (note: 4/05 the 621 epoxy has been replace with our CM 15 epoxy paint) 621 epoxy was used because it has extreme flex which would allow for movement of the surface without cracking. Within a minute or two the epoxy leveled out to a thin, essentially smooth surface. Just under 1 pint (16 oz) of the 621 epoxy was used.

2) after the epoxy was applied the epoxy surface as completely covered with ground walnut shell grit until the epoxy was no longer visible. Two quarts of walnut shell was used (beginners might need more as it takes a bit of practice to get a uniform and even coverage with the minimum amount of grit. The applying of the epoxy and covering it with the grit took 20 minutes (rubber grit could have been used too - about the same coverage rate).

3) Several hours later the epoxy had set and excess ground walnut shell was sweep and then vacuumed up. My wife commented that the resulting surface looked like dark cork. I agreed how attractive it looked (nicely complimenting the brightwork trim elsewhere in the cockpit) and decided to clearcoat the surface to seal it rather than cover the walnut shell with a latex paint topcoat (good quality water based latex is a nice, thin, color stable paint that would 'lock in' the walnut shell grit. Note that in commercial settings the topcoat is usually a coat of epoxy paint). To seal the surface I used our 2 part linear polyester polyurethane - polyester polyurethanes are the best urethanes you can purchase. Nearly 1 quart of urethane clear was used in topcoating the surface as the solvent based polyurethane seemed to quickly soak in/around the exposed walnut shell grit. The resulting topcoated surface was slightly darker and much more glossy than the uncoated exposed walnut grit surface.

The high solvent urethane drained through the walnut shell and formed a small puddle at the forward end of the cockpit. It was 'sopped' up (still very liquid) with a paper towel 14 hours after application. An epoxy topcoat would have been hard in a few hours. Later that day, I 'tore up' a bit of the surface with my shoe heel as the urethane was still not rock hard and it's strong solvents seemed to have retarded the curing of the epoxy below it.

A day or two later and everything is fine!

(4/05 note: other folks have used the walnut shell on their boats and liked the results. One sent pictures!)

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