When doing major or even minor work on older cars your going to run into rust. The steel that is your car wants to turn itself back into the puffy red iron oxide that it was when it was mined. Whether you’re sanding, sand blasting or chemical striping to get rid of the paint and getting down to the metal the first thing you need to apply to the steel is self etching primer.
Self-etching primer is composed of an acid and zinc. The acid, usually phosphoric acid, forces the zinc down into the top couple of molecules of the steel. Chemically impregnating the steel like this cannot reverse the rust but it can stop in from getting worse. So it’s important that you get all of the scaly rust off.
Wipe the surface with wax and grease remover to get it clean enough so nothing interferes i.e. fingerprints. The self-etching primer is usually gray or olive drab gray but the color is just there to show you where you’ve put it on and it is very thin and one thin coat is enough. Putting more of the primer won’t make it work better. You can apply it over paint or bondo but it is only effective on bare metal. You can apply your high build primer or body filler over the self-etching primer but be careful it is not a finished product by it self.
In other words you can’t apply it and then push the car back outside, it has to have a sealed surface over it, water will reverse the reaction and will pull the zinc back out.
Self-etching primer comes as two parts or ready to spray and also comes in aerosol.
I use it when ever I see bare metal or if I’m putting one metal against another. For instance steel screws in aluminum or on welds.
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