The Rot Doctor


Subject: renewing fiberglass deck applications
Date: Tuesday, December 17, 2019


I have an older 1985 trawler, the boat overall is in good shape, except for the fiberglass over plywood decks (in some places). I’ll be replacing the deck over the aft cabin this winter, probably starting sometime over the Christmas holiday. Water leaked in under the fiberglass and damaged the plywood underneath.

I’m trying to figure out what the best application and product would be for my boat issues. The aft deck will be new/rebuilt fiberglass over plywood. The rest of the decks are in decent shape, but I can see what appears to be hairline cracks and/or questionable areas on the boat. Also the previous owner repainted the decks at one time but the new paint is releasing itself from the old surface in some areas (bad preparation), but sticking well in others

After reading your website this is what I’m thinking:

Let me know if this sounds like the correct application and what you would recommend for the final top coat. This will be done in two stages as half of the boat will be exposed to the weather and the repair half will be enclosed in shrink wrap, so weather depending (winter, spring).

Thanks for your advise.


Fiberglass over plywood can be troublesome to repair. Definitely doable, but to get quality results you have to be more careful with your procedure, and more certain that the correct products are gotten where they need to be.

Plywood tends to delaminate before it rots. So with plywood, the main issue is getting the products between the various layers. Fiberglass to plywood, and the plywood layers themselves. We have a fiberglass deck repair section of our website, which is worth looking over if you have never done this kind of work before.

I think that you have the correct products in mind, mostly. A couple of things. We have sold CPES for many years. But due to some technical issues, we have switched to selling S-1 Sealer instead. In addition to this product, and the coatings you mentioned (I would go with the Elastuff 120 as a base coat and either the Elasta-Tuff 6000 or the Rhino Top as a top coat), you will need some of the General Purpose Epoxy Resin (GP Resin) to glue the layers back together, and fill any internal voids. An additional tip, make sure that the inner and outer fiberglass layers are in the position you want them in. Sometimes when the layers delaminate, bows or ripples can form. Once you start with the GP Resin, any deformation will be fixed in place.

For smaller repairs, all this can be fairly simple. For doing larger areas, it can get more involved. Since we have a lot of experience in these kind of repairs, calling and discussing things, before, or during the repair is always encouraged. We want to do everything possible to make sure things go right.