Iíve rolling fender lips and fixing a bunch of stuff hidden under some bondo on the back of my new project car, and Iím trying to make every effort to prevent future rust.
Iíve had to use the stud welder in a few places to get stuff right where I want it (so far everything I finished shouldnít take much mud, really everything looks like Iím just going to wipe it with a skim coat and go, I doubt that I need more then 1/16Ē anywhere, Iím pretty anal retentive when it comes down to it).
What Iím wondering is if itís OK to wipe it down with some metal prep (or if I run into a spot that had more rust even navel jelly) before I skim it to MAKE SURE that any rust that was there is gone? So far Iíve been using a nylon wire wheel (quickly removed bondo without removing much of anything else so I can see what Iím dealing with first) and a 36 grit roloc to cut down to the bare metal where I have to do some work so the surface has a nice bite to it.
I understand that the phosphoric acid in metal prep can do weird things with body filler (keep it from setting up right I think), but they recommend washing it with water to neutralize it, which makes me think that this is all going on on bare metal that Iíd just be causing rust.
What do you guys do? Am I better off skipping the metal prep, just finishing my stud puller/hammer work, hitting it with the 36 grit again and slap on the filler (not sure how much I trust that to get rid of any surface rust that might start while Iím working)? Maybe 60 grit instead of the 36 just to make sure that the grit actually touches more of the surface? Iíd really feel better if I use some metal prep, but I donít wan to hurt anything that goes over it (and this would be a totally different deal if I had the whole body or even a large section totally stripped).