So I finally have the firewall holes welded up and the trans hump transition welded and shaped. Infact I had to cut up the firewall about 1-1/2 inches at the trans tunnel then shape and hammer fit another piece of sheet metal back into that 1-1/2 to go from round to flat at the top of the trans tunnel area.. Anyway I've gotten the firewall finished and ready for bondo so here is my questions, I've sanded, power wire brushed the metal and now ready to move on to the next step. Due to heavy pitting I want to do some bondo smoothing to fill those pits and where I filled holes so should I use like rustoleum rusty primer or rustoleum rust reformer first then come back with the bondo on top? Plans are to use auto base/clear later down the road to paint the firewall. So would I be safe to use rustoleum rust spray bomb, bondo, then filler primer then later on base/clear?
Use quality filler, not bondo, on the areas that need smoothing. When you're happy with those areas, use a quality surfacer. I personally like house of kolor kd series. Block it and if everything is to your liking, paint it. If not, prime and block it again.
One you use Rust-Oleum, stick with it. Nothing else will stick properly to it. If you plan to use a real automotive top coat, stick with it for the primers.
I think you already got the good advice you don't want...use filler, then a good surfacing primer (2K type urethane), if you plan to use automotive paint over the area later.
Don't put filler over rattle can primer. If the pits are rusty, you need to sand blast til you have clean metal. Then epoxy primer or filler. You can use filler over bare metal but it must be super clean. Rattle can/uncatalyzed products have no place in proper body/paint work IMO.
Decide what brand of paint you are going to use if you decide to put a finish color on the car. Then buy that brands version of self etching primer and the appropriate thiner/hardeners etc. Then apply the same brands high fill primer over the etching primer and sand to perfection. Then if you decide to colorize it.........same brand of paint.
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