I completely agree with the other two guys. I have been painting for about 40 years. Rattle can primer may have its place, but that is not on a car. The problem with rattle can primer, and a lot of other primers for that matter, is that they absorb moisture and let air through. Hmm, let's see, what happens to metal when air and water can get to it? RUST. I only do one kind of paint job; down to bare metal and up from there. I always put epoxy primer on the bare metal. It will completely protect the metal. I like
@flingdingo 's idea of different color primers. I use a dark grey epoxy and a lighter grey high build. You really need to get rid of all the rattle can primer and then spray a few coats of epoxy on the whole car. Then give it a few days to totally cure and then lightly block it with a 12-18" Durablock (or similar) sanding block and 220 or 320 paper. Do not go through the primer, this light blocking is just to show you if you have any low spots that need to be filled now. The more perfect you can get the body now, the better the blocking will go after the high build primer is sprayed on. I really like Evercoat G2 high build polyester. Some people like the 2K urethane. Whatever you use, you really do need to get rid of the rattle can primer. If you don't, there is a chance that the solvents from your paint can react with it and react in a bad way. Not worth the chance.
