It's very important to give time for the vapors and thinning agents to release inbetween coats otherwise well this happens. You end up with a crust shell and sponge underneath it. Part of what Pabs said is correct aswell when your finish is too thick. When you polish it does heat the clear which is why a two stage polish works well. You must however on wood not over polish as the clear will not stick to tree as it would steel. I use ntro nowdays due too how thin you can get it to spray.