Ok, this is just an idea.
Epoxy will begin to soften at a temperature above that at which it cured. So lets say the epoxy was cured at 22 degrees C. If exposed to temperatures above that it will begin to soften again. You then apply polyester resin on top of the epoxy, you take the part indoors 24 degrees C, the polyester starts to cure. Most polyester resins reach temps of 60 degrees C once the chemical reaction kicks in. This would cause the epoxy to soften and react with the polyester. Just an idea?
Warren