Auto body repair & detailing: primer paints., light coats, epoxy primer

Question
I asked Mr. Forester a few weeks ago about using epoxy primer on new fenders that were electroplated but forgot to ask him about using the primer over already primed surfaces. I bought a project car that someone had already started and some areas were already  coated with a coat of primer. Also, can this primer be used on fiberglass that  has been primed also? Mr. Forester told me to sand my new fenders with 320 grit. Do i sand all the black off or just enough to scuff them up? Thanks for your help. Fred

Answer
Hi Fred,

Sorry it's taken so long to respond to your question.

I'm not sure if I understand all of your question, but will answer to the best of my ability.

First, in my opinion, the epoxy primer will work fine on new panels. I generally would use a self-etching primer on the bare metal spots and seal the rest of the panel with a primer-sealer, but epoxy should do the job just fine.

Second, the epoxy primer should work well on fiberglass as well, but I would start off with a few very light coats, to make sure it doesn't react with the fiberglass & fillers and lift on you.

Lastly, only sand the new panels as much as you absolutely have to. Leave as much of the factory primer as possible. The more bare metal you end up with, the more likely the part is to rust later on.

I hope this has helped you out. If you have any other questions, feel free to ask.

Good luck, and have a good day!

Aaron