Re: gel coated the hull today.
West System claims that their epoxy is an excellent base for polyester gelcoat. The kicker is that they are talking about after a full cure is achieved, the amine blush has been removed, and the surface has been roughed up. It is strictly a mechanical bond. Which is all you get in a repair instance if you were using polyester or Vinylester resins (unless you can make your repair layup smooth and even with no resin runs or sharp edges).
Anyway, I have been making repairs with West System on the Mako for 3 years now. All of them have been gelcoated and no problems thus far. The first project I did was to grind out all the gouges from the stem (about a 5ft long section up each side about 6". I laid 2 layers of 1.5oz mat then a layer of 6oz cloth to top it off. Sanded and filled, sanded and filled, and sanded and filled. Then sprayed gelcoat. It came out really nice, and hasn't shown any signs of blisters, cracking, or chipping. Its all in the surface prep though.
You cannot spray a mold with gelcoat then lay up the glass with epoxy though, they are incompatible and will not chemically bond to each other or cure correctly for that matter.
I did some repairs for my father in law, and he had already filled some spots with an off the wall brand epoxy filler. The filler was cured and sanded, and I put gel coat over it... The gel coat would not even kick off over that stuff. No cure what so ever! I scraped it all off and tried again. No luck! So some epoxies will not even allow gel coat to cure after they have cured! So West Ststem is correct and their stuff is compatible after cured and prepared.
Heres a new idea of mine. I have heard that vinyleseter is compatible with epoxy as well as polyester. So use vinylester filler over the epoxy or even hot coat with vinylester resin before you apply gel coat. That way the vinylester will be the middle man which both parties will adhere to. Haven't tried it yet, but I am planning to. Just a thought from a fool who hasn't come over the the simple world of painting yet.
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