Urethane bubbling in silicone mold under vacuum

[sp1nm0nkey]

I'm using shinetsu ke-1310st addition cure silicone and innovative elastomers ie-3075 urethane elastomer. I degas the urethane under 29.9 inhg in a polyethylene cup until it stops bubbling (minus the few popping off from co2). Then I pour the urethane into the silicone negative, and pull a vacuum on that, and it never stops bubbling. I was told to hold the silicone negative under vacuum for a bit due to the porosity prior to pouring, but that didn't seem to help. Any ideas?

[awerby]

Silicone molds need to age a bit before they'll take urethane without reacting to it (by creating bubbles). This could be what's happening here. The other thing might be residual moisture - urethane's very sensitive to that.

Andrew Werby
www.computersculpture.com

Originally Posted by sp1nm0nkey I'm using shinetsu ke-1310st addition cure silicone and innovative elastomers ie-3075 urethane elastomer. I degas the urethane under 29.9 inhg in a polyethylene cup until it stops bubbling (minus the few popping off from co2). Then I pour the urethane into the silicone negative, and pull a vacuum on that, and it never stops bubbling. I was told to hold the silicone negative under vacuum for a bit due to the porosity prior to pouring, but that didn't seem to help. Any ideas?