Oddy,
SO what you are saying is that when you took the plug out of the mold you just made, the plug stuck to the mold? Or was this a part that you just laid up in the mold?
If the plug stuck in the mold (
when you made the mold) I would think that the heat build up from the resin might have caused the paint on the plug to get too hot and come off the plug. I haven't used polyester resin to make a mold, but I think it can get hotter than epoxy and this could have caused the wax barrier and/or paint failure and stuck the plug in the mold. I use Part-all #2 wax and Part-all #10 PVA release with a very slow laminating resin (
lower heat build-up). I also had a plug issue in a mold a couple of years ago from using cheap rattle can paint and no PVA on the plug before molding; Never again!!
I would think the polyester resin would be fine, as long as you start with a good catalyzed paint on the plug, good high temp molding wax and a molding barrier(
PVA) on top.
If you have the molds and the first part was what stuck in the mold, I would look at the wax/PVA you used as the culprit of the sticking issues.
Maybe a little more info may shed some light on it.
By the way, how's that donkey getting along these days?