View Full Version : Epoxy pre-coating
I had asked a question on another board and got an answer from someone whose opinion I respect and his answer was seconded by another that I respect so I gotta beleive them. I just thought I would post the question here for all you guys (and gals).
I will be moving my keel (SYP) for my Weekender outside to my open air boat shop where it will be protected from UV rays. I was wanting to pre-coat with epoxy to help stablilize and protect it from moisture. Here is a link to the orginal discussion:
I was adviced not to pre-coat as it would give me a mechinacal rather than a chemical bond when I went to put on a layer of glass. I was also adviced that one layer of epoxy wouldn't protect the wood.
Thoughts and opinions
03-20-2002, 05:49 PM
I think in this case that their chemical bond is more theoretical than reality. It's been my experience that fiberglass adhesion to wood is nowhere near as good as hinted in their replies, whether you pre-coat and later apply cloth to a roughed-up surface or do all the coating and glassing in one shot. Epoxy also doesn't penetrate anywhere near as far into the wood as many people believe. Glass a piece of wood and then pull it off and you'll see what I mean.
Make no mistake about it, if you hit something hard enough to peel or delaminate the glass sheathing from the wood on a pre-coated surface, the result isn't going to be much different, if at all, from one with the best chemical bond possible. The issue that they didn't address, which is probably more important and the reason you asked the question in the first place is all the potential humidity gain that moving the piece outside will expose it to. You always want to epoxy the wood in the driest state that you can get it to. If it sits outside for long, the moisture that the wood picks-up will probably be a much bigger problem in terms of getting a good glass/wood bond than pre-coating or not precoating and getting the mystical chemical bond between resin layers - and we haven't even covered the possibilities of dimensional stability, warping, etc. I'd put two coats of epoxy on any piece of wood that I intended to move outside and leave there for a while before glassing.
03-20-2002, 09:32 PM
Assuming the boat will be living outside, I would let the keel stabilize in your open air shop for a few weeks before coating it. Then I would coat it with either one coat of epoxy or CPES. The idea of coating is just to slow down moisture absorption and loss and to keep the wood from checking until you are ready for the final finish. Chances are you will sand off most if not all of that first coat preparing for your final coat. The chemical/physical bond argument won't come into play until you are ready to do your final finish.
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