First make sure you are using epoxy resin and not polyester resin. Poly will melt EPS foam. You are experiencing exotherm of the resin which is melting your blank. Read our Epoxy tips (particularly #3 and #4) and as soon as you mix the resin dump most of it out on the blank so it is not concentrated in the bucket and getting hot. A thin layer of epoxy will give you plenty of working time to fully saturate the cloth.