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Originally Posted by swamp rat
Ok I chased every last pin hole I could see with a light shining from the back side, what a pita! Recoated everything with GEM and its drying overnight.
Is there a difference between self etching primer and Acid etch primer??? One in the same?
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I think, generally speaking, acid etch (or wash) primer refers to products like the GEM Rustkiller which is a mild phosphoric acid that converts the rust and helps keep the metal from forming new rust in moderately dry environments. You may also hear the term alodine coating in the same sentence with acid etch primer, although I've personally only seen it applied to aluminum.
Self etch primer usually refers to a coating that cures and has a heavier film build (thickness). Unlike epoxy, it is typically a single stage coating with chemical additives that grip the metal tighter than lacquer or 2K primers. It is a suitable base for most subsequent layers of primers / paints.
Some two part epoxy primers don't adhere well to metal that has been treated with phosphoric acid and has residual iron phosphates on the surface. So if you want to be safe, don't squirt epoxy over the GEM without first wetting the surface with a mild solution of GEM and water, flushing it thoroughly with water and then allowing it to dry for 24 hours. Some epoxies don't care, but I don't have a thumbs up, thumbs down list, so treat them all as if they are sensitive to iron phosphate.
Techniques for prepping bare metal for paint are varied and success depends on what's underneath and what's intended to go on top of the bonding layer. New metal with no history of rust can be treated to a much different regimen than old rusty, pitted metal.
The one thing you can be sure of is that rust is the worst where moisture gets trapped between two layers. We've all seen pictures of old cars in fields that are rusted all over. However, the metal on the exposed surfaces is often in surprisingly good shape. But down at the bottoms of the doors and adjacent to any double walled construction, the rust will have created blisters and gaping holes. So proper metal restoration means not only replacing or neutralizing the rusted metal, but also finding and fixing the source of the rust... which is usually water migrating from somewhere above and collecting in the tight spaces. If you don't address the root cause, you're wasting your time.