Hey boots,
I sealed that particular board with epoxy/microballoons, 1:1 ratio by volume, looks like marshmallow creme. I have also used Dap Fast’N’Final spackle, and both have strengths and weaknesses. These are my personal impressions of both:
Epoxy/Microballoons: much stronger than spackle, but less good for cosmetics, and harder to sand. Also less forgiving. Best to apply it in sections if you are doing it for the first time, because any drips/uneveness you leave will be a bitch to sand, as just as you sand the drip flat, you sand into the foam right next to it…That’s why the right side of the board pictured is so crooked near the tail, I tried to do it all in one shot, got lumps, sanded lumps badly; it was a 10 footer, and I should have done it in sections. If you add some white pigment, the cosmetics look much better (can’t see as many of the foam beads). Also, if you are airbrushing on the foam, epoxy/microballoons works better as far as masking goes (adjacent/multiple colors), with the harder surface.
Spackle: Much more forgiving to use, easy to sand, leaves the blank bright white (can’t see the foam beads), and you can keep re-applying and fine sanding until you get a surface smooth enough to do good looking resin tints. Not as hard a surface, though, so spraying adjacent/multiple colors can mean trouble, with the masking tape pulling up the paint and spackle underneath it from the previous color. Also, you can spackle both sides of the board at the same time, saving time, but the downside is since the spackle is thinned with purified water to make it easy to spread, the blank soaks up a lot of that water. You have to let it dry or you can have epoxy blush/bloom problems from the moisture left in the blank.
Your choice, but either way, mask off your stringers/noseblocks/tailblocks, both methods tend to ‘dull’ their appearance…or just get a 2.5-3+ lb/cu.ft EPS blank and you don’t have to seal.
Also, I would advise you do your artwork on your first few on top of the hotcoat, if at all. That way you can sand off mistakes, and you won’t be hard pressed to do a perfectly clear lamination. It’s very hard the first time (hell, anytime) to not froth up the resin with lots of tiny bubbles that look like a cloudy, whitish, haze, especially the laps…
If you do the artwork on the hotcoat, you will open up a whole new can of worms when you are wetsanding/polishing it if you sand through the gloss coat, so I did all the wetsanding by hand on that board…
Good Luck, and let us know how it turns out!
JSS