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daimon1054 04-01-2004 04:41 PM

Never use body filler on metal??????
I have read that filler should be done on bare metal then you primers done but while watching TRUCKS on TV the other day the host said that you should put epoxy primer first then do your body filler and that way the filler was encapsulated and you had less chance of rust and lifting.

So what is the right way? I have always put filler on metal.

poncho62 04-01-2004 04:44 PM

There are theories on both methods.

Fact of the matter is, that you shouldn't have to put on so much bondo, that it's going to lift out in chunks.

daimon1054 04-01-2004 04:52 PM

Never said chunks:D

Centerline 04-01-2004 04:57 PM

Stacy was correct. Bondo is porous and can trap moisture inside. When you prime the area (if the bondo has been applied directly to the metal) the moisture will promote rust from the inside out. If you seal the surface first with epoxy primer the bondo will adhere to the epoxy just as well as the bare metal and any moisture thats trapped in the bondo won't be able to reach the metal surface and will eventually just evaporate.


poncho62 04-01-2004 04:57 PM

Sorry.....thats the way a lot of people use bondo................

[email protected] 04-01-2004 05:00 PM

Move to California - don't have any moisture in the air here!

Grusome Goat 04-01-2004 05:25 PM

Some epoxy primers such as R&M cannot be sprayed over filler as it will lift it, while to my understanding according to my jobber PPG products can be sprayed over filler, so alot depends on the chamical compounds used in the different manufacters. Chack with you're local paint store as to the products they carry and what is compatable.

jc55 04-01-2004 10:07 PM

I've been using filler over PPG DP50LF. I would almost go as far as to say, I think the filler actually adheres and feathers better over the epoxy than bare metal.
I think it's a great method to use over patch panels, rocker to quarter seams, tail pans, etc. Places wher moisture attacks from the other side.

Kevin45 04-02-2004 01:25 AM


I think it's a great method to use over patch panels, rocker to quarter seams, tail pans, etc. Places wher moisture attacks from the other side
Bondo should not be used to fill holes. And if you have problems with moisture attacking from the other side then some metal needs to be replaced. Bondo should only be used as a filler for low spots and then sparingly. If rust holes are not removed then the chance of the rust getting larger is almost 100%.


jc55 04-02-2004 02:42 AM

I agree 100%. But I'm not talking about rust. I'm refering to new metal. Those of us buying a gallon of dp50lf or ncp271 usually aren't the ones bondoing over rust;)

Realistically, you may have lap welded seams or have the slightest pinhole here and there from spot welding a fresh panel.
All of these areas are prone to water intrusion. Ecspecially on those with replacement panels.
(I was born and raised in Ohio Kevin. I know it can get pretty bad out there)

If you can butt weld and grind a 7ft long lower quarter panel, or a rocker to quarter joint upside down without a few tiny pinholes in your seam, you're good.

BarryK 04-05-2004 03:47 PM

Body filler over epoxy
Applying epoxy to the bare metal and than applying the filler is always the best choice!
Mercedes and Porcha have required this for warranty work since the 70'S. Now six months ago Toyota requires it.
Here is why.
Body filler will stick to epoxy (unsanded) better than metal.
Body filler is not air tight and solvent s are never totally released (air and solvents equal rust) if they were it would crack. Have you ever sanded a ten year old body filler job and noticed the metal corrosion?
Another thing the epoxy does for a body filler is it makes it more flexible!
A word of caution: Never use filler over an acid etch type primer or a lacquer primer.

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