Hi Jason, the only thing I have ever cast was plaster of paris. I know that some folks have made molds and filled them with Great Stuff but the mold has to be sturdy and air-tight for that to work. What are your molds made from...plaster or latex?
Hopefully Vlad will get on here and put in his 2 cents, he's the mold master

He has a how-to page on mold making that may help you
http://www.hauntproject.com/projdeta...olding/Casting look for the Terror on Beechwood page.
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