I asked Gougeon Brothers about that and I got some info sent back to me. As long as you get a fresh surface on the polyester you shouldn’t have any problems. So, sand it down a bit, don’t touch the spot to be adhered to with your bare hands or greasy rags and you should be golden! Now, the other way around is a different story…a little more critical on the sanding to get through the amine blush that occurs on epoxy, but I think still doable. Vaya Con Dios! Mark “Mad Dog” Pearson