As I'm stripping the paint off the car I noticed some bubbles on the surface of the paint. When I got down to bare metal I noticed black spots in the metal. Took Ospho and put it over the entire fender and let it set an hour the first time and it didn't do anything to the black spots so I did it again and left it on over night. Still no success. My question is do I need to remove the black spots from the metal and what do I use if the answer is yes.
Grind it off? Some look a little deep.
