Another question regarding the '89 Civic project, which is now in the process of being painted. I've applied several coats of U-tech primer over the original paint (sanded first of course), then applied a thin guide coat, and sanded that to highlight the damaged areas. There are tons of dents - some of them must be close to 1/16" deep - and filling them with primer would take forever. But I've read that body filler will adhere to primer, if properly sanded and cleaned, so I'm wondering if it might be better to just fill these dents with body filler, then sand, prime again, and move on to the topcoats. The car is now in someone else's garage and I don't want to tie up their space any longer than I have to. Thanks for any advice.
You can't trust _any_ body filler to work over _any_ primer (lead over lacquer primer, for instance, would be a disaster...), but _some_ body fillers will do a superlative job over _some_ primers. In fact, there's every reason to believe that the _right_ body filler over the _right_ primer would do better than many body fillers over bare metal.
Unfortunately it's been 20 years and I can't remember brand names. You want to use a primer that adheres well enough to the metal to have the body filler hanging off of it, and body filler that not only adheres well to the primer that you're using but that your primer will stick to.
(note that some combinations of plastic over plastic are complete disasters -- epoxy seems to inhibit most polyesters from curing out, so if you try to stick the wrong filler to epoxy primer it'll all harden except for the interface between the filler and the primer, and make a big gawdaful mess).
If you're buying your materials from a decent paint store as opposed to a cheapo auto parts outfit then they should be able to point you to the right combination.
Pay attention to toxicity -- epoxies and other catalyzed paints/resins have a life-long cumulative effect that doesn't cause you a single problem when you're 25, but which can force you to change careers or give up favorite hobbies when you're still relatively young. (others will just drop you dead). I've dodged the epoxy bullet, but if I use too much cyanoacrylate glue (superglue) all at once I get a reaction, courtesy of a too-loose protection policy while building model airplanes in my teens and 20's. Now I use it sparingly, and build far slower as a consequence.
If it's the same old lacquer primer putty that I used to see used it works great, but it shrinks a bit -- so you have to go over deep spots (1/16" is deep) more than once.
And you still have compatibility issues if it won't stick to what's underneath, or if it melts when you apply the next coat of primer (although it's great with lacquer primer, obviously).
You can get body putty, too. It doesn't harden as hard as Bondo or other fillers, but is used for finishing before final painting. If it goes on thin enough, it hardens anough to last for 5+ years.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.