Postby foam-n-fibre » Thu Dec 15, 2011 6:48 pm
I built lots of windsurfers with that stuff in the 80's and 90's. Be careful, though, it is not all created equal. I seem to recall that the blue Dow stuff came in 2 compressive strengths, 20 psi and 30 psi, or something like that. Actually, if you check their website, at least here in Canada, you'll find many different types, some up to 100psi, for going under foundations (much heavier though). But, in terms of what you find in the big building center, here there are sometimes 2 different weights. If you don't go with a sandwich construction, try to find the heavier of the two.
Above answers have been great too. They are sensitie to heat and the foam does off-gas over time, potentially leading to delam in the long run. Also very true that you need some structure for the resin to grip in, don't sand it super fine.
If I was making one for kiting, I'd put 2 6oz on the bottom (or a 4 and 6?), and might throw in a 1/8" corcell deck patch with a layer of glass underneath and 2 more on top.
As for bonding the stuff, I've only really used epoxy. Seams at shallow angles suck for shaping. Some of the later ones we did involved using 4" foam with vertical glue joins, so if you want you could put glass in the join and have stringers every 4".
I MIGHT build a surf-type board with this stuff. If I do, I would consider trying to use a single piece and having a rocker table to form it to, to bend the rocker into it while glassing. Not sure tough, have not fully thought it through.
Peter