I need help! I am stripping down some old doors of there paint. A heat gun is doing a good job of removing the numerous layers of paint. However, I have come across a layer of what Im persuming is a prima and when I heat this is just goes sticky and gummy. Basically, it wont come off. I have tried a chemical paint stripper and it does absolutely nothing to it at all. I have tried an electric sander and again no result really. Can anyone point me in the right direction?