Smelly and messy is all I can say about that stuff. Make sure you get some ventilation and/or wear a respirator when working with it.
In preparation for the foaming process, I am filling the grooves (fluting) I made in the outside of the hardboard wall pieces with Bondo to help strengthen and keep their shape if things ever need to be disassembled. The filler foam will be sprayed on top of that and then shaped with hand tools and automotive finishing sanding blocks (used for body fenders and such).
Learjet 45 Shell (Now with Bondo!)