To seal or not to seal, that is the question...

Builder's Forum
1

...with apologies to Wm. Shakespear. I'm about ready to 'glass the outside of the hull of the fourth duck in the fleet, and I've done it both ways, but I'd still like to get opinions: What are the pros and cons of applying a seal coat of epoxy and sanding the raised grain BEFORE putting on the fiberglass cloth -- or putting the 'glass cloth over the unsealed wood and working the epoxy into the weave and the wood at the same time? If doing it both at once is just a time saver, that's not a factor for me. The real question for me is which way provides better adhesion. It seems to me that doing it over bare wood lets the epoxy seep into the wood and create a better bond with the 'glass, but I've had the experience of returning to a section that I thought had adequate saturation only to find that the wood had absorbed enough epoxy to leave the 'glass a little starved for epoxy, and subsequnt attempts to fill the weave still left it showing through. So, what's the collective wisdom?  Thanks.

Jim

2

I would always put the cloth onto dry wood, for the 'pro' you describe. It also avoids the risk of getting amine bloom under the cloth, which would be a disaster.

On the inside, I often put the tape onto wet fillets, wet the tape, and then wet the inside surface of the hull, then cloth onto this wet epoxy. I probably wouldn't do this on the outside, as I couldnt get it round the compound curves.

3

One rationale for sealing seems most pertinant for stripped designs- the thought being that the bare wood might absorb too much of the initial epoxy and "starve" the lamination. I tried glassing with and without a seal coat on the inside and outside of a cedar vessel and didn't detect a difference. With plywood I would guess there'd be even less concern. I suppose, too, that going overboard with the seal coat could also compromise strength and would just add weight. Says the guy with little experience and no real data before him...

Best,

Patrick