Rust Converter Recommendations. Aerosol for sun faded/surface rust car.

Ddaddy said

Phosphoric acid converts rust (orange oxide) to black oxide that creates a barrier to further corrosion. That’s what the POR products use to achieve their results.

Just spray with phosphoric acid in the nooks and crannies and carry on.

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I agree but be careful coming back with an epoxy primer that an react to the acid. Call Southern Polyrethanes and they will tell you that a reaction can occur with their epoxy primer. They recommend if using the phosphoric acid sol. (Ospho), then wet it all down good again with the Ospho and follow right up with a water bath to neutralize the acid.
I am no chemist but I have also been told in other places, the the reaction might occur of the epoxy prime contains any acid. I really have NO idea if any epoxys contain any acid!!!
I had a rusty hood a few years ago, I hit it with a DA 80 grit, came back over it with a big wire cup on the right angle grinder, there was pitts (rust) in the metal. I wiped it down good with Ospho. DID I let it dry overnight???? Don't remember. I coated it real good with Plain ole Rusteolum , the real stuff in the Gal can. After it finally cured, there ere some places the R. enamel sorta wrinkled. It sat outside for months, the R. kinda faded as usual, but it all was stuck on there like ugly on an ape. Point is, there was some reaction between the Ospho and the R. in a few places, and it all was darn near impossible to sand off when I later tried. Interesting experiment.