The Stovebolt Site Forums The Shop Area Paint and Body Shop prep for Epoxy Primer

I"m working on the doors for my 53 project truck. They are mostly covered in surface rust, but are otherwise in fairly decent condition. I'm curious. If I take a stiff wire wheel to them, knocking off the worst of the rust, then sand them smooth, will that be clean enough for epoxy to adhere well. I"ll say that they will be 95% rust free bare metal at that point. There's a small number of spots that have small pits. Those will still have a little rust in them. In the past, I've normally sand blasted sheet metal prior to applying epoxy. But this time, I don't really want to sandblast the doors.

I would sand with 80 grit down to 220-320 grit, then use Metal- Prep to clean and etch, then water wash, when totally dry shoot the epoxy.

If Metal-Prep is phosphoric acid based, be sure that the epoxy used is tolerant of that. Even washing down with water may not get rid of all the iron phosphate, which most epoxy doesn't go well with. I don't think you'd need to go as file as 220 or 320 grit with your sandpaper. Generally rougher is better for paint adherence.

The Metal - Prep that I have used leaves a zinc phosphate surface, I have only used one type from the auto paint supply, possibly other sources have a different chemical make-up.

Epoxy primer is designed to adhere to properly sanded …. Scratched bare metal. Sometimes you can use an acid based primer to etch the metal but sanding is best. If you have something between the metal and the epoxy, it won’t adhere properly and anything you put on top will have problems. All of your money products are on top of the primer so if the primer fails to adhere, you loose a lot…. And it looks bad.
You can use phosphoric acid to get to the hard to reach spots then sandblast but you run the risk if leaving the residue ….. just where you don’t want it.
Mechanical metal preparation by sanding, sandblasting is the best way.

Mike