What are the upside/downside of using these materials for a kite/surfboard?

I've cut model airplane wing's with the blue one before ; may
be a bit too light in density for a board ?
Unless maybe Ya place a Bunch of ply-wood supports from top skin
to the bottom skin in order to keep it from being crushed.
Also maybe if Ya cut the blank length-wise and then wrap each section
with 5 oz carbon like they did on that video a bit ago. should be easy
to find that.

Bille

I built my first kite surfboard (directional) back in winter of '99 using a 2" thick panel of blue. I shaped it while flat. It had a natural concave on the "bottom" so I kept it. I used 1/8" Divinycell for the bottom with 6oz glass under it to set the rocker. I used oak veneer with 6oz glass under it for the deck. I think I finished with 2 layers 6oz on the deck with extra patches under the heals and 1 layer of 6oz on the bottom. Using epoxy for the layup. Paint (I think I used water colors) and simple rice paper graphics under hotcoats.

It actually turned out better than other DIY boards or any other board I tried. I rode it exclusively for 3 years.

Thanks gents,
For gluing pieces together what would you use? I presume epoxy, but I would like something a bit faster as my epoxy is very slow hardening.

You can use XPS, cross linked polystyrene, the blue/pink foam
from the home center for a surf board style shape. You will need
to very careful with leaving it in the sun, letting it get hot, etc or it will delam.
finish sand your shape with 40 or 60 grit, to leave some tooth for
the epoxy to adhere. For a surfboard, 2x4oz on deck with a 4oz
deck patch, 1x4 on the bottom. For kiting, look into a sandwich
style board with a wood veneer deck, for straps, either bury a
high density foam or wood insert under the lam.

Do some research over at swaylocks on xps boards.
Good luck with the board.
Pete

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

There is a good reason not to use this type of foam. At first glance it sounds good but it will totally delam after a while. The blowing gas will escape and end up between the foam and your layup.

As strange as it seems EXPANDED polystyrene which is blown beads does not do this. If you use the 1.5lb/ft3 expanded and any sandwich construction like a wood veneer and you are golden. Go to swaylocks and mine the posts there. Lots of people have been down this road of hard knocks.

You mileage may vary.

Stan

Mileage may vary is true. I have one windsurfer in the garage still from 1996 which has no delam. Some other boards delamed in a year or 2. I would only consider making one with this stuff if it was a quick job on a budget, without using any fancy materials. It might last well, but then again, it might not....

If you DO make one, make it white and don't leave it in the car or in a board bag where it will get hot.

Peter

I think the foam from the early days had a different blowing gas that was bad for the ozone but good for cores. I too had a few windsurfers that held up fine but then after that change it was crap. As far as I know all the epoxy surfboards that are styro these days are expanded beads of 1.5-2lb/ft3.