Yep, I did a board with that stuff…It sounds like Dow brand Styrofoam (the white beaded stuff is NOT Styrofoam, Dow has the trademark on that brand name, it’s their extruded foam, which does not have beads) It does tear easily, but usually a gentle touch remedies that…80 grit sandpaper works really well, use a gentle touch when surforming…
This is not the beaded stuff, so don’t spackle the surface, you will just get a weak bond. One of the biggest draws is that it does not take in water whatsoever.
Don’t forget, you have to use epoxy. Poly will melt the foam…
The stuff has really good physicals–good dent resistance, strong, stiff and light. I made my board stringerless, with 3x4 oz bottom and 3x4 oz deck, with a 6 oz deck patch, and it’s a little lighter and WAY stronger than a PU / polyester board I have that’s a similar size.
The other problem with the stuff is that nothing sticks to it very well, and since it doesn’t take in water or any liquid, epoxy will not seep into the foam at all. The usual solution is to leave the blank rough sanded, and baste it before glassing it, really squeegeeing the epoxy into the foam, hard. I went an extra step, and cut shallow parallel razor cuts into the foam. the resin went into these grooves, creating a physical bond with the foam. I did some peel tests before glassing, and this produced the best result, big hunks of foam were coming up with my test strips.
I would not reccomend this stuff if you are going to be in a hot area. Apparently it gasses out when heated, and will delam. I live in San Francisco, so no problems—I’ve been surfing my dow board HARD for about three months now and it’s doing fine.
There’s plenty of discussion about it’s utility as a foam in the archives, with advocates and foes, and what I took from it all is that it’s great for backyard boards, but not reliable enough for production. I think the production guys would love to use it because it has the best physicals and does not take in at all, but the delam issue has not been solved.
BTW, I managed to get a four inch sheet, and cut the rocker in six slices, then glued them up sideways to make my blank. (as if I had five stringers, but they are just glue-lines) I clamped a rocker jig on either side of the 4" block, and used wound guitar string in a sawing motion, running along my rocker templates. The friction with the foam heats up the wire just enough to cut, and no nasty fumes. (if you hotwire, USE A RESPIRATOR! AND VENTILATION! the stuff gives off nasty fumes. basically if you can smell it at all, it’s too much. I think there is cyanide there, as well as other stuff!)
hope this helps…