I am having a real problem with rust on my old F150. It's a 95 and I just got done grinding off the paint down to bare metal yesterday to try to fix it. I couldn't get any metal conditioner before spraying on epoxy primer. I couldn't find any of that stuff. I put on one good wet coat and then my compressor blew a line. Darn, I hate my air compressor. I got it from harbor freight. So, I got one really nice coat on. It looks super. Very smooth with no runs. I wanted to get another coat on and get some paint on, but couldn't. Rats, now there are two little bubbles where some of the rust once was. Why is this?? Moisture is all I can say. I am going to sandblast the area to give it another shot. Is this happening because I didn't use metal conditioner and didn't have time to get a coat of paint on? How long should I wait before topcoating? It doesn't really say on the paint can, about an hour? Thanks for the help guys. I want to get all the rust to go away on my truck and I was hoping I could spray it with some epoxy primer and then be able to do some body filler work before spraying on some paint. Is this possible to do in time without these bubbles and rust coming back through? I am about ready to just get some new sheet metal.