I have made my plaster of Paris molds and they turned out great. I am now in the process of making a two part injector mold. The only issue i am having is after i have poured the plastic, bubbles start to seep through the plaster mold. I know its not the plastic itself but rather the plaster mold. What should i use to seal it properly? I have tried five coats of clear nail polish and a gloss spray paint enamel. Neither have worked 100%. Both worked slightly but wore off quick. Should i maybe try Mod Podge? what do you recommend. Thank you !