Helping a friend paint a bathroom. She removed some wall paper and there are multiple damaged spots on the wall. The paint underneath is about 25 years old and is a flat white orange peel that seems very hard and durable. I was going to use GARDZ on the exposed paper. Question: Since the wall has so many places like this, can I GARDZ the whole wall of will the GARDZ have problems adhering to the original paint that is present around all the bad places?