Starters,.... it's not the first time I've painted a car. I've got a car that had significant surface rust on the roof. ( Bad pic - you get the idea. )



The other day I spent some time with 80 grit and removed the top layer of rust.



Once I got to the 'electro-coating' ( or whatever it is ) I continued to sand until getting thru to the bare metal. It seemed as if there was still a layer of rust between the metel and the electro-coating. The area circled in red looked like the area circled in white before I sanded thru.



I just kept at it & sanded the whole roof back to metal.




As soon as it was completely sanded I coated it with spray-bomb Primer/Sealer to inhibit any additional rust from forming until the car is more ready for paint. Sanding it back to metal took all afternoon, but removing the Primer /Sealer will take very little time using a couple rags soaked in Acetone.

There is very little rust anywhere else on the car other than little spots here and there. I expect to sand most of the previous finishes off ( paint & clear) and leave only the electro-coating on the rest of the body. The plan is to coat the car in high build 2K primer and top-coat with a single stage eurethane. ( Solid color, no clear, heavy top-coat so I can wetsand it for days. )

Question,........

What should I do about the bare metal areas before priming the WHOLE CAR with the 2K primer ??

In the past I've used spray-bomb etch coating on all bare metal before applying primer. Never had a problem; but would like some input from those with more experience before I prime it.

 

Bare metal must have either etch primer or epoxy primer applied before spraying high build primer. Rattle can primer/paint offers little corrosion protection especially in the long term. For proper protection of bare metal, a 2-part primer should be used.

Rattle cans have their place, but priming/painting the exterior of a car isn't one of them.

 

You need to use a product to treat the rust that is still present before you prime over it.
That's step one. It is impossible to just sand it all clean.

Talk to your local paint supplier and they should be able to suggest something, and then use an epoxy primer to cover it all.