Fresh Paint bubbled where bondo was beneath...Any good body guys here?

tylert14 · 10-27-2008, 04:44 AM

Let me start off, I'm not a body guy.... but I do body work lol

I basically did all the body work then had a buddy of mine that paints lay down matrix primer/sealer/paint/color blender/ clear.

Turned out out pretty good but a few flaws on my end turned up and were going to repaint it this winter. I know everything I did wrong except for 1 thing. The pain bubbled in 2 spots on my rear 1/4 panel. There is bondo below both of bubbles, and metal work below both bubbles as well.

I've been reading and from what I get out of it moisture from poor metal work caused the bondo to bubble. You can't push or pop the bubbles.

So is that what hapend? And what can I do to fix it? Can I grind the bondo in the affected spots down to metal then use some kind of sealer on the metal first then body filler? I DO NOT want to have to paint my car a third time.... lol

SSquid · 10-27-2008, 06:32 AM

bubbles are caused by bad body prep normally....

SPDEMON · 10-27-2008, 04:52 PM

Either moisture or most likely SOLVENT under the paint trying to get to the surface. You need to sand, clean, feather the repair again and then when you clean the body repairs, make sure they are completely dry and free of solvent before applying any primers/sealers.

If you have a compressor, make sure to blow air on the repair AFTER you solvent clean it, then use a tack cloth over the repair right before you spray sealer or primer.

BMR Sales · 10-27-2008, 05:15 PM

It can also be caused by too much hardener mixed in with the bondo.

tylert14 · 10-28-2008, 04:58 AM

I don't think it was solvent under the paint. I'm pretty good at prepping the surface before paint. The thing is in the one spot it was bubbled in the same spot where it allready had bondo under the paint from a previous owner. That bondo got ground off and I noticed the metal beneath it had been welded. The other place it bubbled was from a small rust spot I cut out and welded a patch in place. That's got me 99 percent sure its moisture coming through the weld. What I need to know is how can I seal the metal before putting down a filler. Can I put down epoxy primer then bondo over top of it? I have allways been under the assumption bondo will not "stick" to primer.

BMR Sales · 10-28-2008, 10:07 AM

Yes you can put body filler over epoxy. It will actually have better adhesion over the epoxy than it will over bare metal.

BradsLS1 · 10-29-2008, 07:09 PM

I have seen this before. You said that you used mud on the area's where it had been fixed by welding. It was moisture from the back. I wouldn't be surprised at all if when you grind that off again you will see rust. You have to make sure that the weld is tight no pin holes at all and have to make sure the back is painted the correct way. If you can get to it. If any of this is not followed your going to get moisture from the back of the panel and it will eat to the front. Bondo is like a sponge it will soak up and hold moisture. Using a primer before bondo will help but not the metal. Take care of both sides.