Hi Bob,

See my comment in the other lead about home-built beachcat. If your Hi-load 60 and 100 foam is of the extruded polystryreen version then it is by nature unfit for board or hull construction (closed cell). Twenty five years we already tryed this type of foam in surfboards and we jumped them after 10 times in two pieces!
Here in Europe we know the foam also from Dupont in a green version.

Personally I have a great deal experience with this foam in building a highspeed trailer from this foam which broke the speedrecord for trailers on the road. I had to beat the foam on forehand with a steelbrush in order to create holes for better connection with the laminate. That is to say, after first removing the very thin rollerskin of the foam due to its fabricationmethod.

I think that the foam you mean is or PolyUrethan foam (clark foam for surfboards) or PVC foam which is known for its high pressure load. Weight of these foams are always a threshold for using it other then in sandwhich cores.

regards ronald