The Rot Doctor


Subject: Delamination in plywood cabin structure.
Date: Mon, 18 Jun 2001

My 41' sailboat has a plywood cabin structure which is now thirty years old and showing it. The plywood was protected with fibreglass when new and painting over the years has provided some protection to the flat surfaces. It now seems that water is penetrating the plywood and causing delamination from the edges. The cabin top to cabin side joint is covered by teak trim. The plywood is delaminating on inside and outside surfaces, spreading mainly from this joint. After rain there are black streaks running down the cabin sides from the teak trim line. I assume this means the glue has gone away and water is getting into the edge of the ply and causing rot. Any suggestions? I would prefer to spot treat the ply rather than replace the cabin top completely!
Regards, John S.


Yes, what you are describing is common. It's what plywood does!

The treatment is, actually, fairly simple. Remove the teak trim and any paint from the edges to be treated, allow the ply to become dry, and then treat with CPES (Clear Penetrating Epoxy Sealer). Allow the wood to absorb all that it will. You may have to just sit there and keep dabbing at it until the CPES starts to pool. Allow a few days for the epoxy to vent away the carrier solvents, and then put the teak trim back on. If there are nail/screw holes, those should be treated with the CPES as well. You can paint right over the cured CPES. It acts as a prime coat.

Inside you would follow the same procedure. Be sure when working inside the hull that you have good cross ventilation. You should probably use a cartridge respirator, one capable of filtering organic fumes.

This process should solve your problem. We have tested CPES on plywood in many different ways and it always prevents delamination and rot.

Come back if you have additional questions.