If you are getting bubbles then you are pouring them in. It's possible you are getting the plastic too hot too fast......or you are shaking the heck out of the container an putting the bubbles in the plastisol before you even start. If you see a bunch of bubbles coming up, stir for a bit and nuke for another 15 or 20 seconds. This will thin the plastic and allow the remaining bubbles to rise to the surface as you stir some more. Stir, don't whip and if you have one, use a metal butter knife.