Correct me if I am wrong, but when Clark Foam or whoever makes their close tolerance blanks, they use a very hot wire to cut the blanks out of a larger block of foam. The heat from the hot wire is what causes the foam nearest the outside of the blank to be strongest. If this is true, would it be possible to heat the blank after you rough shape it to again make the foam nearest the outside stongest? It would seem, this technique would allow one to make concave decks that weren’t so fragile.
From what I know the conventional blanks (like Clark and Walker foam)are molded, not cut, and the skin strength/density comes from the foam compressing when it expands and meets the surface of the mold. I think that you are thinking of polystyrene and styro blanks when you refer to the hot wire cutting method.
yeah they look more like there blown in a mold not hot wire cut…i cant say i know why the crust is formed but im shure its not cut with hot wire…so if u want a stronger board leaving a little of the hard smooth crust must help …but as far as heating it to melt it to a hard shell .? well im not an expert but that sounds like a bad idea.
WARNING: Never hot-wire polyurethane foams (Clark/Walker). One of the vaporized compounds contains cyanide. Toluene-Di-Isocyanate also could be present and is nasty stuff…
It would be best to get a different foam blank than a Clark to shape a concave deck. Walker foam makes polyurethane blanks with a constant density throughout the blank, so you could shape it however you wanted and the foam still has the same structural integrity. Or you could cut your own polystyrene foam blank, those foams are also constant density foams. http://groups.msn.com/thegrasshoppersurfboard/shoebox.msnw