I have some Micro Mark CR-300 urethane resin I've been using for over a year. Recent castings have tiny (less than 1 mm) bubbles just below the surface of the bottom of the piece, i.e., next to the detailed part of the slush mold. I've squeezed the resin bottles to get as much air out as possible. Is there any cure? Sanding causes the bubbles to expand and once their surface is open I have not been able to fill or seal them. BTW, I greatly prefer CR-300 to any alternative I've tried: little smell, easy to work (a little softer than model car styrene).