Not sure what kind of coatings you deal with, sounds interesting, but some of these automotive coatings and phosphoric rust treatments do very little other then putting a coating on top of the rust. If you scrape them off or sand through them there's still rust. Maybe they help, but blasting or replacing to the end of the rust seems to be the best, for me, solution. Some can cause adhesion problems if not neutralized properly.
Wipe it down with phosphoric metal prep to remove flash rust, then neutralize with water. Ok, I'm right back where I started lol
We deal with making a car baby lol. So right as the car is being stamped & constructed, we sell the pretreatment the bodies are dipped into and treated with; Zinc Phosphate & now thin film zirconium technology. In my mind, nothing was as good as the old Zinc Phosphate from the the late 80's up until the early 90's. The Ecoat which went over that layer was also better- had lead in it.
That's just it, if you're sanding stuff down to bare steel, you're already at a disadvantage. The doors, fender & bedsides were galvanized, which is just a fancy way to say they've got a layer of sacrificial zinc on top of the steel which helps slow corrosion down when it does start. If you've ever seen those Mercedes Sprinter vans, you'll know why it's important. Those things seem to rot right from the dealer lot, least the early ones did. Seem to be steel bodies only. So a homebrew repair on old sheet metal where someone has grinded away all the rust and such, slathered on filler or welded in patch metal, that is going to rot right out if exposed to elements. There's no waterbreak free cleaning, no awesome phosphate, no zinc and no ecoat.. At best, just some crappy 1455W wipes, primer surfacer, primer sealer, basecoat and clearcoat.. The paint sold to OEM's had to meet strict standards. The **** sold to aftermarket jobbers & paint shops doesn't have to meet anything, except color. Something to keep in mind..
