I don't know what type of plastic that you are using. also if you are staring too much you are going to get a lot of bubbles in whatever you do when you're stirring do not use wood use a metal steering rod also like it said above if your mold for not properly made so the air can escape when you are shooting you are going to have problems make sure that all the error can escape properly again do not over mix your plastic. I won't get into the issue on plastics but some of the different plastics have more bubbles than others when you are mixing them. in which mold are you having problems with.