Fixing Bubbles

JimKueneman

Mopar Nut
Well my Coronet is going on almost 8 months of the SPI make over and the other day I was Fast Waxing it and noticed on the rear quarter panel way down low behind the rear wheel a rather large (to my way of thinking) number of bubbles under the paint developing :(.....

I did metal work in that area so I am having a hard time believing it is rust coming back through, especially with the number of them. The car has not seen water since I have restored it. The panel was solid but it had some weak places and I patched it. My gut says the problem is I really suck at welding almost upside down (the panel rolls under the car in this area) and I have some places where I did not get all the residue from the weld out of a few pinholes here and there and it is outgassing. I did fill the area with waterproof fiberglass reinforced filler so I should have filled them but.... Just won't know till I dig into it. I should have bit the bullet and sandblasted the area after I welded but I only wire brushed and sanded it.

Question are should I completely strip the paint from the area, rework it or do I just work the areas with the problems and sand off what I need to? The car has a really sharp body line about 12" up from the bottom behind the wheel so there is a perfect place to blend it in and make it impossible to tell I reworked. Even a if the color does not exactly match the change in angle at the body line make the hit this area radical different anyway so it won't be noticeable.

Thanks, from what I read this is not really an uncommon thing to occur. Is that true?

Thanks,
Jim
 
Why the need for FG filler over welds? I hear people recommend that on quite a few forums and I never got it..
 
Why the need for FG filler over welds? I hear people recommend that on quite a few forums and I never got it..

It is so if you get pinholes in the welding (which turned out to be amazingly easy to do) it will seal them up so moisture can't get in behind the paint.
 
myth . fiberfil type fillers are just as porous any any other filler. i shoot epoxy over welds and rub it into any pinhole.
 
I treat the back side of my welds by rubbing in a little 3M 8115 panel adhesive to address any porosity in the weld. It is not affected by moisture. If I can only get to the front I really work it in and then sand it to only leave it in any pinholes etc.

Yes Robert I know this should not be needed if the welds are perfect but I do my best and then use the panel adhesive for insurance....

Don
 
No disrespect to anyone, especially Jim, but this serves as one of those harsh lessons learned. Porous welds hold crap. Don't fix them by covering with a band aid. Grind out the weld and have another go until it's right. Paint materials are expensive, weld issues are cheap to fix before the paint goes on...
 
any rust repair you can see from the outside is actually 2-3x's larger on the inside. I always remove a lot larger area then must think I should. this will allow for a clean weld pass. Always look at the back side for any rust if there is it needs to be tended to.
 
any rust repair you can see from the outside is actually 2-3x's larger on the inside. I always remove a lot larger area then must think I should. this will allow for a clean weld pass. Always look at the back side for any rust if there is it needs to be tended to.

I can't get to the back side in this area which is part of the problem I was having.
 
I always use a flashlight to look for pin holes. I always double check after sand blasting. Sometimes grinding can smear pin holes shut, but blasting seems to open them back up.
 
My gut says the problem is I really suck at welding almost upside down (the panel rolls under the car in this area)
Sometimes you have to be creative to get in position. In this case you could jack up just that side of the car as high as possible, and lay on a creeper under the weld area with some splatter protection laid over you.

I can't get to the back side in this area which is part of the problem I was having.
Paying close attention to the back side of the waste coming off will help a lot here, at least to give a clean weld line.
 
Another thing I do when I can't reach the back of a repaired panel is spray it with a good heavy coat of 3M Rust Fighter 2 cavity wax using their wand and a schutz gun.

Don
 
All you see is bubbles, the real answer will be when I decide to start digging into them. It will be only conjecture till then. I will share what I find. I don't plan on doing anything till the fall anyway.
 
Guys I had a revelation after looking at the photos I took of the restoration. Let me know if this makes sense. This is the rear quarter behind the wheel were it rolls under the car and meets the trunk extension. I welded up some small rust problems along that bottom edge but it was almost upside down and I sucked at that welding. I did the best I could, cleaned it and then skim coated the bare metal with fiberglass filler (I did NOT cover up rust, it was shiny metal with welding pin holes). This was to "seal" from moisture (haha). I shot the epoxy over it did the body work and painted. After that was done I got nervous so I mixed up more epoxy and literally poured it into the cavity between the trunk and inner quarter panel to seal it up. I bet what happened was there was so much liquid and took so long to dry that it got through the pinholes in my welding soaked in to the filler and behind the outer layer epoxy separating it from the filler. This makes sense because I could not justify the size of the bubble. There was just NOT that much rust in that area to come through that fast in that amount. After looking at the photos the bubble is right where the filler is. So there question is what would you do? The bubbles are not visible when viewing the car, you only know they are there if you lay on the ground and look up. The car will only see rain if I make a major mistake in weather forecasting. I am thinking to just let it be now that it is done. Nothing has changed over the last 4 months since I first noticed them.

Does this seem like a plausible reason and path forward?

Thanks,
Jim
 
that filler sucks up moisture the same as polyester filler. i've been bit by duraglass too. grind it out epoxy the pinholes full and repaint .
 
Grind it off and I bet you find a problem you are seeking the answer to. Only you know what you did and how well you did it. So I say grind it have a close look you may even have to poke at it with a knife tip or something to find out what you over looked. From there fix it right and learn from it, we all have had to do it one time or another.
 
I want to get this straight, the short strand filler was put on bare metal, to seal the pinholes?
Yes, advise from a bodyman (not here). Much of it was sanded off. Now I realize putting the epoxy primer front and back would have accomplished the job in a much better manner.
 
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