When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
What is the correct process for priming? What i mean is do i prime over small dings and dents, and then use filler and prime again? The other approach is to do the filling, getting the body nice and straight and then priming. Which is correct? I like the idea of epoxy priming to protect the metal forever, and then using filler and re-prime....but if the filler won't stick because of the primer then that's no good...
First you want a max thickness of 1/8" or less of body filler. I use a stud welder to pull out dents then body filler directly to bare metal. Some body fillers tell you to bond only to bare metal due to heat generated. Then metal prep bare metal, epoxy primer (2 coats), 2 coats of 2K primer, then base and top coats. I like the 2k and epoxy primers different color. I want to know when I'm getting close to epoxy primer, don't want to get into it.
You can do bondo work on bare metal or epoxy primer, but both need to be roughened up to give the bondo something to adhere to. Some guy on one of the forums I frequent did a test where he tested the bond strength for applying bondo directly onto bare metal and on top of epoxy primer coated metal and he found both techniques worked very well and there was no clear winner. To test the bond strength of the finished test samples, he bent by hand and struck the 6'x6" test panels with a hammer to test the bond strengths. I tend to prefer to epoxy prime first before any bodo application, since I know bondo can adsorb water if exposed, so if it does absorb water it will not be in direct contact with the metal surface.
If you are just fixing a dent then apply the mud to the bare metal and prime over that, but if you are stripping a car down and restoring it, spray the bare metal with vinyl wash (NAPA martin senor product) It is a very old fashion rust inhibitor but there is no better spray on rust proofing available anywhere. I guarantee you that any bare metal sprayed correctly with vinyl wash will never rust ever. Over the vinyl wash, spray a good epoxy primer/sealer. Then mud over the epoxy when dry, but you will have to sand it first, I would use 320 grip paper.