I have been messing with bodywork and paint since I was a kid. I was taught to grind a panel down to bare metal before using body filler. About 10 years ago I noted a trend where guys would do their metal work, sand the panel to bare metal, prime it, scuff the primer and then apply body filler. After speaking to many people about this it made sense to me as there would be less of a chance for corrosion to get between the primer and the filler as opposed to bare metal. I have been doing it that way ever since. If I am doing a big project I go through the effort of mixing epoxy primer suitable for bare metal and shooting the panel. My question is this. When I have a small repair to do, I sand the area to be filled to bare metal. Because I don't want to bother with mixing primer and cleaning the gun for such a small area I have been using rattle can self etching primer and then scuffing it and applying body filler over it. Does anyone know if this is proper. I have not had any problems with the filler reacting to this primer but I wanted an opinion on this. Thanks and Merry Christmas
Aside from careless front line repairs the trend of filling over primer came with epoxies, zinc rich primers or plating are always tricky to overcoat because the zinc wastes in a cathodic reaction and any deviation from manufacturers overcoating specs is potentially disastrous in my experience.
Hey, As you may or not know, not all self-etch primers can be covered over with plastic filler. The acid in some etch primers is far too reactive, and will peel the plastic filler. Be sure to read all you can on any paint product you use. Using "rattlecan" anything under an automotive finish is like tryin' to cut a deal with the devil! Most of the content of a rattlecan is propelant, not the zinc or ***anium oxide or acrylic resin you think you're paying for. I too, have been putting filler over well ground metal for nearly fourty years with good results, however I don't live in the "land of ice and snow". I was always lead to beleve that a mechanical bond was superior to a chemical one, but over the last few years the paint and body products have changed majorly! S****ey Devils C.C. "Meanwhile, back aboard The Tainted Pork"
Evercoats new Quantum fillers have an epoxy added to them to increase corrosion resistance over bare metal. They meet up to OEM specs which is 500 hours in a salt spray. Most fillers last about 200 hours. They sand way faster (about twice as fast) than traditional fillers as well.
Hey, One guy drives a Ford, the other drives a Chevy...... The HOK is probably the Lincoln/Caddy of the three. I know of guys who spred plastic over epoxy all the time with no ill result. I'd sand the epoxy with 80 grit production paper prior to the plastic. S****ey Devils C.C "Meanwhile, back aboard The Tainted Pork"
I haven't had any problems at all putting filler over PPG DP epoxy primer and DuPont's epoxy primers. Oh, and also Kirker epoxy primer (which is a lot cheaper) seemed to work fine under filler. Usually I have the metal work pretty close though, so I haven't ever had the filler thicker than about 1/8". I don't know if it works okay for people who like to slather on pounds of bondo. I scuff and scratch up the epoxy primer before spreading the filler over it to give the filler something to grab onto. If you read the data sheets for a lot of those epoxy primers, they even recommend putting the filler over it. A sales rep guy from PPG recommended I do it that way when I talked to him at a car show about 10 years ago, and I've done it that way since. It makes sense because bondo can absorb moisture, and if you can keep moisture away from the bare steel, you should have less corrosion problems years down the road. Epoxy primer is really good at sealing against corrosion and holding up to salt spray tests. If when you're sanding the filler, you sand all the way through the epoxy primer in the surrounding area, make sure you get some more primer on it soon before the bare steel has a chance to corrode. My method is to do the epoxy primer, then do filler over that, then when the filler and sanding is all done, shoot a few coats of Evercoat Generation 2 polyester primer over it, then sand that, then a sealer, then paint. I'm no expert, but I do read the product data sheets and talk to the guys at the paint store who used to paint cars for a living.
Yeah, that's what I've heard too. It's okay over epoxy primer, but you might run into problems over etching primer due to some chemical problems. When you say "zinc oxide" primer, do you mean zinc chromate? I think they've removed the chromium and lead compounds from most of the paints lately. Like the greenish DP40 primer I think used to have zinc chromate or lead in it, but now all you can buy is DP40LF (lead free). I think if you stick with epoxy primer, you'll have good luck. If you don't want to buy an expensive name brand like PPG, DuPont, or HOK, I think the Kirker stuff isn't too bad for about half the price.
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