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I have been sanding 2 layers of paint and sealer off of my project car. Once I get down to original paint, I use it as a guide to find the irregularities in the metal, dings small dents, scrapes. I then work on fixing those problems along with any rust.
Rusted metal is replaced. Bondo used to smooth out. Any bare metal is primed with etch primer except where bondo is needed.
I then spray sealer on after all body work is done. The sealer has set past it's spray window, I plan to spray a sanding filler primer on and do a final block and wet sand on the whole car, once I get to that point.
My question is, since the sealer has set for so long, what would be the best procedure to insure a good bond? I don't think a scuffing would be enough, but I dont want to sand the sealer off. Is there a chemical method to let the next coat get a bite on the sealer? Can adhesion promoter be used on primer instead of plastic?
 

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A lot of sealers aren't good over bare metal. As far as the time window, contact the manufacture.
 

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In my experience, yes, your going to have to sand your sealer. I dont think you need to go crazy with it but you should do something to give the next coat of whatever something to bite onto. I would NOT spray adhesion promoter on it. Adhesion promoter for plastic is some nasty stuff. I think it would just melt your sealer and make a big mess.
 

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Sand with 180-240, on a DA sander where possible. Or consult the primer's techical data for recommended grit range when preparing an existing finish.

Whether "sealer" means cured epoxy or urethane, that ought to work for a urethane primer-surfacer.
 

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Take it back down to bare metal and the skim bondo.

Prime it and work up.

One of things where doing something that might work is not worth the expense of paint and clear when it does not.

Take it back down and work up.
 

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Take it back down to bare metal and the skim bondo.

Prime it and work up.

One of things where doing something that might work is not worth the expense of paint and clear when it does not.

Take it back down and work up.
^^^This^^^
 

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Depends on the "sealer". If it was sealed with epoxy, just sand it and go. if it was sealed with non-sanding sealer, take it off, and start over. Or squirt a coat of "Jamb It" on there and run with it. (like Earl Schieb) LOL
 
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