Working on my son's 66 GMC pickup and have a question. I've ground all the paint off the door and am welding and gluing patch panels on. I have a fiberglass strand waterproof filler and PPG Omni AU epoxy primer. Should I prime the door and then use filler or use filler on the bare metal and then prime?
Dave I'd check the procedure page on that primer. Some epoxy primers aren't designed to be topped with filler. DP series epoxy primers are. Some fillers aren't meant to be applied over epoxy. Best bet, ask the EXPERIENCED paint rep. I used DP40(lite coat) under the filler on my car. The car has a new quarter installed around '74 and when I stripped the car I had to rework the filler. When I removed the filler, there was plenty of surface rust under the filler. It gets trapped as the filler hardens and creates condensation.
I think the correct procedure is 1) sand to metal 2) prime the whole thing to prevent flash rust 3) sand to metal and apply filler to areas as needed 4) repaint the areas you filled. The main goal is to prevent rust from forming by leaving lots of bare metal exposed while filling. I'm no body expert though. Or you could just get a can of spraycan filler-primer and spray globs of it on :laugh:
Here's a picture of the installed quarter after I got the filler and the rust off. You can still see traces of rust in the picture.
The material sheet for "MP170 Epoxy primer" says " Background- MP170 is a two component, gray non-chrome epoxy primer designed to provide adhesion to cleaned and sanded bare metal, fiberglass and painted surfaces." Then for " Compatible substrates" it says "Cleaned and sanded steel, galvanized, aluminum, fiberglass, old finishes, and body filler." I bought the primer and filler from a body shop supply store and was told I could prime and then fill. Then I looked at www.autobodystore.com and they suggest filler first. I talked to a body man today and he says prime then fill because of what you found on your car. When filler hardens it gets warm which may cause condensation to the bare metal underneath which of course rusts eventually. The data sheet for the primer seems to say it can be used over or under filler so that doesn't seem to be a concern. I kind of like the idea of having the primer on the metal first to avoid rust so will probably go that way but I'm going to call my supplier first just to double check. Thanks for the replies.
One important factor with epoxy primers is to let them dry thoroughly before putting anything over the top.
