The Rot Doctor


Subject: CPES and Bulkhead installation
Date: Thu, 09 Nov 2000

I'm just about to start installing 3/4" and 1/2" marine mahogany ply as bulkheads into a bare hull of polyester glass layup. The hull was laid up in 1976 and I just purchased it from the original owner who never got around to building his boat. I just came across your web page tonight and read that CPES is more effective than git rot in sealing plywood bulkheads. I've also been told that epoxy is a better choice when tabbing bulkheads to a glass hull as old as the one I'm completing. My concern is: In using epoxy I've been told I can't use an alternating mat and roving tabbing schedule because epoxy and mat aren't compatible. I read on your site that CPES and polyester based resins are not compatible either. I want to use mat with roving because of the increased bonding strength associated with that lay-up schedule. Can you offer any solution to the conflict of mat with epoxy and CPES with polyester.
Michael Y.


Here's the way it is:

1) CPES (Clear Penetrating Epoxy Sealer) can and should be applied to your bulkheads before installation, after they've been cut and trimmed. Special attention should be paid to the edges and the end-grain areas, since this is where deterioration/delamination usually gets started. CPES is MUCH more effective than Git-Rot.

2) Epoxy is by far the superior choice for tabbing bulkheads. Much stronger than polyester, and, if you use a resin like our Layup & Laminating Resin, it retains just enough flexibility to keep it shatterproof. Our resin also has a long pot life and remains blush-free.

3) Epoxy will adhere to a cured polyester surface quite well, as long as the surface is rough or scuffed and is clean (wipe down with lacquer thinner or acetone). BUT, polyester resin will NOT adhere well to an epoxied surface.

4) Epoxy and glass mat are usually incompatible because the manufactured mat contains some chemistry to bind it together, and this is incompatible with epoxy resins. Mat is generally used with polyester resin because it can capture and hold a lot of resin quickly, and it takes a lot of polyester resin and cloth/mat to give strength. Epoxy layups are so much stronger than polyester layups that you can eliminate the mat sequence without worry.

So, the bottom line is there is no conflict with putting epoxy on polyester, but there with putting polyester on epoxied surfaces.

Come on back if you have additional questions.