I'm going to strip the car down to bare metal and start from there with the painting. Do I need to remove the old bondo too? There hasn't been too much yet, just around what looks like a few small dents and dings. Can I spray the etching primer over it, or does that need to be completely on bare metal. The bondo looks to be in good condition. Just wondering if I need to disturbe what has already been fixed. Thanks, Dan
I reworked my bondo when I stripped my car. The bondo was 30 yrs old and probably absorbed some of the stripping chemicals. That will come back to haunt you when you prime or paint. I used epoxy primer UNDER and OVER the bondo when I reworked it. Bondo is made of products that absorb liquids, like water. When I stripped the bondo, there was a mild layer of rust under it. That's how much it absorbed while waiting around to be painted. The urethane primer that I used has etching chemicals in it also, so it could be used on bare metal. Plus, I added a phosphate coating before priming for extra corrosion resistance.
Water proof bondo Someone told me there is a water proof bondo available. If it is, would it be better applied to the bare metal or on top of the primer. JD
You should strip everything to bare metal......just think how pi$$ed you'll be when old bondo starts falling out shortly after you apply $500 worth of paint! Also, never put bondo over primer. I grind any metal under bondo with 36 grit and etch it first with "tripletch" so it sticks well. I haven't had any fall out yet and the paints been on my car almost 4 years so far. They make a lighter 2 part filler specially made to go over primer that I have used called "pirhanna putty"....3m makes it. But by the time you sand it out, you end up with bare metal around the edges anyhow. It's always best to take the extra time to do do things thoroughly and not take chances on old work that may not have been done correctly in the first place. :bglasses:
Oh yeah.....that waterproof bondo? Isn't really waterproof, I know that from experience........and it is very hard to sand. :bglasses:
I've read that all new cars have bondo applied over Epoxy primer,because the chemical reaction when bondo is mixed with hardener creates heat,which causes condensation=rust.
I won't pretend to be an expert on this subject......I'm not a body man or a chemist.........but it would seem to me that in order to get moisture, air would have to be present. How can air be present under body filler when it's against the surface and all the air is displaced? The metal would absorb the heat anyway. But then again, given the thin metal newer cars are made of, it doesn't take much rust to make a hole.......I guess they can't be too careful. ou:
I don't know,thats just what I've learned in the Auto body class I'm taking.I guess because the metal is cool and the bondo is warm then condensation forms.(?)It's in books so I'm going to trust it.
There is some validity to that. When bondo is applied, it's wet. When it hardens, it's dry. The moisture has to go somewhere. If you've ever checked out bondo with a high power magnifying glass, it's porous. I was told years ago that bondo is made of plastic talc products(powder). Very absorbent. Another reason that it must be primed well with a good primer or the bondo will absorb the paint causing "die back". When I stripped my car, every spot where there was bondo on the car had rust under it. I metal prepped with a phosphate coating, then applied a lite coat of epoxy primer, then the bondo. The primer info sheet even states that fillers can be used on top of the epoxy primer. It helps adhesion as well as protects against corrosion. Some plastic fillers say apply to bare metal some say use over properly coated metal or epoxy. It's best to go with what the filler manufacturer and paint manufacturer recomends.
Bondo can be applied over epoxy primer but not over other types of primer.Metal should be ground with 36 grit where bondo will be applied,Epoxy sprayed on allowed to dry fully{most important step},then put bondo on.If Timepoxy is not dry the bondo will cause it to lift off the metal.
I never "grind" the metal beneith my bondo. I went to Autobody school and was never tought that. I've worked in a body shop for 2 years and I've never seen anybody grind before they lay puddy. Puddy will stick to anything. If you need the extra grip that 36 grit will allow, you shouldn't be using bondo. :Smarty: You should be pulling out the pannel. Never use spot pudy either. It never drys. Glazing puddy is the best. Old Bondo may have a problem sticking because of old chemical compounds but the new stuff is fine. Also in school we never stripped all the way to the metal unless there was a problem. If you sand down too deep you can great flat spots. ou: We'd sand until the problem was gone. The old paints are Acrilic Laquors. Some primers are Laquor. Thus there is no need to strip it off. Primer will promote adhesion if anything else. I would sudjest metal etching primer. (eats rust) :TU:
First off all laquar should be removed or the paint you put on top could soak in to the old paint and cause future die back problems.Second if the old finish is cracked the new paint will eventually sink in to those cracks.READ your paint manufacturers warranty they will not warranty over laquer. Second bondo needs more than smooth epoxy for goo adhesion Iwas taught that in auto body school and plenty of GM and paint company certification classes.
sealer A sealer is a good choice when repainting such an old car. It makes a solid seal between the old and new layers.
It's always a good plan to get rid of laquer underneath, as it's a "solvent sensitive finish" and not compatible with a catalyzed topcoat. Also on another note, a person never wants to use a self etching primer over a sandblasted surface.
Hey I never heard that one before,what is the reasoning behind not using self etch over sandblasting. I have done this on small brackets and stuff with no bad results.
Self etching primer I was told that the acid is absorbed into the pores of the sandblasted metal and the primer skims over and dries with the result being that the acid is trapped. I did it a few times myself and didn't notice anything, of course all I did was prime and never did topcoat the parts. Doesn't Sikkens only offer acid etch primer, not an epoxy primer ? I think the Lesonal line may have both, and the U-Tech line I know has both.
Yes sikkens does offer a epoxy primer its called autosurfacer EP.One thing never to do is put epoxy over etch primer a friend found out the hard way that it don't work.
i dont have all the air sprayers to use good 2-part primer, can i use spray paint primer and do all the body work to prevent the metal from rusting, and then have the painter spray good primer over the spray paint stuff
Rattle can primer is fine to do what you want ,but keep the car dry cause if it gets wet it will start rusting under that primer.
