The Rot Doctor


Subject: boat construction
Date: Thu, 30 Jul 1998

I am in the process of building an 8ft sailing dingy. The hull covering is luan plywood. Before discovering your page on the web I had already given the hull 1 coat of polyurethane spar varnish. Is it too late to use your penetrating sealer on the hull and would your lay-up epoxy give a nice glossy finish to the boat?
Thanks for your help.

It's really too late to apply the penetrating epoxy (CPES) -- the varnish will limit its penetration considerably. I wouldn't worry about it though, at this point. Go ahead and finish off the boat, and then watch your seams. When the poly starts breaking down and coming off, you'll need to scrape it away and at that point you can apply the CPES and then re-poly over it. It's a new boat so hopefully that should take awhile. Put on at least five coats of the polyurethane, though.

Epoxy applied to the polyurethane doesn't make much sense, since it will only stick to the poly and then would have to be re-poly'ed to protect from UV light. Anyway, you'll get a smoother finish by layering up the polyurethane, with light fine-grit sanding and wiping between coats. Follow the directions on the can label.

Anyway, I'm not a big fan of applying raw epoxy to wood. It's hard to get it smooth because of the density and temperature considerations. As a coating combined with glass cloth, yes, but that is a structural issue and your boat specs don't call for it. Just finish her off with the polyurethane, pop her in the water and have some fun!