What I've learned about epoxy, catalyzed paint/primer, 2 part silicone, fiberglass resin is that ANY contaminant can be what goofs things up for you. In the matter of 2 part silicone it can mean it will never, ever set up no matter how long you wait. Actually it seems to get more watery. And the contaminant can be as simple as a bit of Elmer's glue left in a seam of the mold tray or oil from your fingers, a bit of moisture, lint, dust, nearly anything foreign. Very sensitive stuff. In the case of fiberglass resin some contaminants can prevent hardening for as long as two weeks or more. Except for IMRON or DELTRON, that is. I painted a lot of that and the only way you could prevent it from setting up was to forget the activator. In fact two years ago I found what remained from a quart of PPG DELTRON black left from 1998. It had been stored in the garage the whole time. The fellow at English Color said there was no hardener that would work with it today and that the paint had probably deteriorated beyond using. Curious, I tried some hardener I was using with some catalyzed primer. Uncertain of the strength, I added in to the paint at 1/2 the suggested amount, thinned it and it set up fine overnight. But as Jerry correctly said, you have to remember to clean your gun. Good luck!
