Ed has made a good and important point. Even for solvent two pot epoxies, the thicker the coat, the slower the cure. So building more coats on un-cured coats will only make the problem worse. In single
pot epoxies, the solvent, water
or whatever used, is there to hold the crosslinking chains apart and stop them linking. If the solvent is trapped, the chains don't link. Something that can help is heat. It speeds up the movement of the molecules and thus the chains come together and link faster, but once again, if the solvent can not escape through the skin, it is either trapped in the film making it porous or it stops or slows the cure process.