I am at a point where I am ready to put filler on some of my rear fender weld seams on my 49 Chevy. I have a dilema going at the moment. The weld seams are quite long and cut right through where the inner rear fender and exterior fender section meet. I suspect there are some small pin holes in that seam, but I am having some problems.
It is difficult to see if there are pin holes or undercut for sure. If you are looking at the seam from inside of the car, there is a small space between the inner fender well and outer fender. The area is not accessable because of the way the body comes together. I can barely reach my hand in there, and not even to the half way point. I was going to try and roll or brush on some POR15 and then seam sealer between the two body sections to ensure a sealed seam, but I don't think I can even get a brush or roller in there. I could seal the interior side of the metal with some of the 3M inner body cavity that has a long spray tube, but that does not take care of potential moisture problems if there are any pin holes. I have been trying to fill (weld) them but unsure of that specific area. I have thought about using various body fillers, but that would not eliminate the potential rust behind the body filler if moisture was able to penetrate from behind. Anyone have any ideas or experience with this problem. I have even thought about using some metal panel adhesive from the front to initially seal the seam, but I was unsure of the compatibility of filler on top and or paintability of the adhesive. Probably a nutty idea anyway.

One last note. I have been shining a light from the outside of the panel to identify pin holes while looking at the weld seam from inside the body. If you are not looking staright at the seam, pin holes are hard to identify. Because of the lack of ability to get a straight on look at this area, I am unsure of any potential problems. Any ideas recommendations on this one?

If the underside of the seam is bare metal I would first treat it with a sprayable etching primer like PPG makes. I would follow that with a good epoxy primer. You can then spray a lesser quality paint to seal it all up.

Vince

I would do that if I could. The problem is that I cannot get in there. The best I could probably do is get a fog in some areas. I cannot get straight at that area, I can barely reach my fingers or hand in there while stretching my arm out. Think of reaching into a hole and trying to paint the sides of it. Maybe I will just end up fogging it.

I'm at a loss like everyone else! I would lead it but not sure you can so I will give two Ideas.
Spray the outside of seam with a coat of epoxy. Let set overnight and get some Duramix 4227 Flow seam sealer and with a spreader spread a coat over the whole seam. Next day DA of with a 180 grit and spray a coat of epoxy over the seam sealer before ANY filler is put over it. The epoxy will act as a barrier coat and allow the filler to stick-filler will NOT stick to Duramix, well it will until first day in sun.

Best of worse idea.
Second option is BRUSH (soak the seam) a coat of epoxy, let set overnight and spread a coat of chopped fiberglass over the seam such as Duraglass or kity hair.

Can't believe I gave this advice so everyone go easy one me!
Can't think of anything else.

A further note I missed as I'm not use to epoxies requiring acids etches. Find one that don't.