Bare Metal Preparation
Okay, your automobile body is stripped down to bare metal, now what? We need to get some kind of sealer on it to prevent surface rust, which can occur rapidly depending on weather conditions. It must not get wet, so keep it out of the rain. But what about humidity? If humidity levels are high, surface rust can start almost immediately and you could notice it overnight. You need to get a sealer on it to insulate the bare steel from the moisture in the air. How do we do that? The following methods are ways to seal bare metal.
Note: If a chemical metal conditioner for rust removal was used, be sure to neutralize the acid in the metal conditioner.
Epoxy Primer - There are many brands of epoxy primer...I’ve used several different ones, all with good results. It likes to have an 80 grit finish for proper adhesion. This can be accomplished by sanding or abrasive media blasting. I like the epoxy best because it has more body to it and seems to protect the metal longer, which may come in handy as restoration projects usually take a little longer than just a simple repaint.
Etch Primer - This seams to be the “old school method” but still works. It, too, likes to have an 80 grit finish for proper adhesion. Being thinner, it's a little easier to weld through making fabrication a little easier, however, I still prefer the epoxy for the extra protection.
Sometimes I hold off on the primer/sealer on bare metal, if I’m going to do fabrication to the body right away. It's better to weld on bare steel, rather than steel with primer on it. After fabrication is complete I always follow up with a little media blasting for a final clean up of the panels, and to clean up all the welds prior to primer/sealer.