Originally Posted by 64falconsix
Ray , I know not the correct area to ask but I did not see the site search or I would have looked it up, I plan to cut out the rust and replace with good metal but in the areas where there is some slight surface rust and pitting I was wondering what the best procedure was. I had thought about either blasting or wire wheeling the small area ( chips and scratches ) that have rusted and a few places where there is surface rust coming up. I was searching if the use of a phosforic acid to make sure the rust in the metal pores or bottom of the pits is dead and gone is a bad idea.... maybe because of later adheasion problems or un nuetralized acid. any advice? I currently have 3 coats of paint to contend with 1 the original 2 a repaint and the last paint which was a single stage uerathane, does this need to go back to the bare metal?
If the surface rust areas have pitting, you need to get the rust out of the pits...You mentioned that you have experience with welding and fabricating so I'm going to assume that you have experience with sandblasting. If 80 grit on a DA (Dual Action Orbital Sander) doesn't clean up the surface rust and get into the pitted profile I would sandblast...as I'm sure you know if you sandblast there is a chance that if done incorrectly it could warp the metal...done correctly there shouldn't be a problem. I haven't had the best of luck using a wire wheel on pitted metal to remove rust.
As far as using an acid, there is a product that many swear by called OSFO if I'm correct, I've never used it my self but you could look that up on the forum. Anything I've done in the past if 80 grit on the DA or sandblasting doesn't clean up the surface rust, I don't consider it surface rust anymore and replace the rusted part of the panel by welding in new pieces...(I feel that if either of those 2 methods don't work, the pits are to deep and the metal is to thin...that's my opinion, others may disagree).
As far as having to deal with 3 existing paint jobs...I would say it's time to take it down to bare metal and bring it back up using a quality sandable epoxy primmer immediately over the properly prepped bare metal. That way you know exactly what your substrate is and don't need to worry about, 1 factory paint, 2 a repaint and 3 the single stage urethane paint job that's on it now...just to many variables in the substrate and the old paint is getting thick.
These are my opinions, others may have different views, I'm expressing what has worked for me over the past many years and now it seems most of what I do is older vehicle restorations and customs.
Hope this helps to start, we can get into much more detail whenever your ready.