Repaired Quarter Panel Rust Issue

[2Bad4Ya]

We replaced the quarters last yr on the 68 & we did not use full quarters. We used 80% quarters and seamed it to the car above the rear quarter body line.

Today I noticed some bubbling on the driverside rear quarter up in the seam area. I coated the underide of the weld seam back before we put the inner fender in, but could not get to the section above the plate that extends out from the hing area (I dunno how to best describe it).

Anyways it just so happens that the one area I was not able to coat from the underside is now producing some bubbles under the paint. I figure it is most likely rust since I have not had any other bubbling or other issues with the paint.

How is the best way to tackle this issue, and is the fact I can not coat the underside of the weld going to cause me problems in the future?

Is it an issue that a welded area may not have a coating/protection and could cause rust on the backside... could that cause rust on the outside? if So how can I prevent that in a situation where I can not get to the unprotected backside?

I assume to fix the outside I will need to grind out any filler in that area and a bit out and then treat the metal and refill and paint/feather that area?

Suggestions etc... appreciated, just a couple of shadetree mechanics doing it at home.

[Denvervet]

someone with more exp will chime in about the fix but a suggestion on coating hard to reach welded seams would be spray epoxy primer then use the wax that can be sprayed with wand extension in that area. Messy but could work. Having replaced both my quarters, fender wells, etc not sure where a spot could be that you couldn't get some seam sealer on it. When I say sealer I mean one of the 2 part good quality types..fusor, 3m, etc

[2Bad4Ya]

Yeah I was able to get all the areas along the seam, except for this spot. The section in the upper corners by the trunk hinges. There is a square plate/brace that covers that section of the welded seam, it is to tight to get a spray or brush between the plate and the fender. It may be touching even, at any rate no way for me to coat that section.

[dhutton]

If your had any porosity in your welds and then applied filler directly over the seam then it may be moisture causing the filler to expand. Did you apply epoxy primer before you applied the filler?

[2Bad4Ya]

yeah, i am not having any other issues any place else. I hate that I could not get to the backside and coat it. I can fix the issue by grinding it down to the metal etc... but that does nothing to make me feel better about it not happening again in that spot.

I am anal like that, maybe I can bend that plate down enuff to shoot some primer up in there and then bend the plate back.

[monteboy84]

More likely than anything, you have a pinhole in your weld.

[2Bad4Ya]

That is possible, but how would you approach fixing it? I plan on grinding out that section to remove the rust, but I need input on how to best prevent it from coming back since I can not get to the underside and coat it. Otherwise I fear just filling back in and painting it will just fix the current issue and not prevent it from happening again.

More likely than anything, you have a pinhole in your weld.

[dhutton]

I don't think it's rust, the body filler is swelling due to moisture wicking through porous welds (pin holes). Did you use butt welds? If you did you need to fill in any voids and then coat with epoxy before you apply filler. Body filler absorbs moisture and then it swells. It needs to be fully sealed from moisture on both sides. Applying body filler to bare metal is bad practice in my opinion.

[2Bad4Ya]

Yeah sorry I forgot to reply that we did apply an epoxy primer before skiming the weld seams.

[TnBlkC230WZ]

I'm no expert and if it is rust, you will have to cut it out. IMO, sand it down until you know you've gotten to clean metal. Cut the section out and but weld a new piece of metal in.