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Mystery rust bumps

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TulsaFred

TulsaFred

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Put the epoxy primer down on the engine compartment today:

2jccaom.jpg


However I noticed an odd problem. Rust bubbling up under the inner fender panels on each side, almost mirror image:

4j18wx.jpg

11tbp0x.jpg

20uqq1d.jpg


in a row as if there were a row of corroding rivets or something, but I can't see any obvious cause. The other side (fender well) of this area has a reinforcement plate, but no fasteners or anything to explain the odd linear arrangement of corrsosion.

Anyone else see this problem or have thoughts?

Fred
 
Only thing I can think of is spot welds.
 
It must be corrosion between the inner fender and the reinforcement plate on the other side of that panel. It seems to follow the edge where it's spot welded pretty consistently. There's usually no seam sealer on the edges so moisture probably got between the layers.
 
Could be the solvent in the paint reacting with the rust and junk inside the holes in the sheet metal. Probably best to cut it out and weld in a new piece. This problem is not going to go away quietly.
Cheers,
Scott in CA.
 
Fred

Saw you photos...looked familiar. Went to the garage to look at my 66 Sprite rolling tub...identical problem to yours on the drivers side. I believe that Gerard is correct in his diagnosis.
 
What really puzzles me is, as good as the rest of it looks, I'm surprised that you didn't see some sign of it before painting. Normally epoxy doesn't react badly with hardly anything. But it does sound like Gerard is on the right track.
 
Did this car get dipped by chance?
 
Not so sure I think the painting (epoxy) caused this. I expect that the fresh paint just made it easy to see ie shadows.
 
I saw the lumps prior to painting, but I needed to get a coat of epoxy primer on to keep rust from forming all over the bare metal. I knew I'd have to repair this before a second coat of primer.
Doesn't have anything to do with the paint.

So far today I've cut out a strip of the panel over the "lumps" with a cut off wheel and cold chisel. Then I removed all the rust underneath using a combination of die grinder, angle grinder and wire wheel.

Sure enough, it was a double row of spot welds holding the reinforcement plate to the inner fender, just as Gerard said. Water comes in between the panels (from the fender well side) and settles in between, then attacks the metal from the spots welds out.

Surprisingly little structural damage to the metal. Here are some pics of the project so far:

250v8t3.jpg

2ic38eo.jpg


I coated the area with some Rusotleum Rust Reformer, I like it. There was only some tiny residual rust down in the seam between the panels. After cutting the strip, I separated the panels using a chisel to get well clear of the rust. Toward the bottom I ran into a hard seam that prevented any more separation. I wire wheeled the crevice then applied the Rust Reformer.

Next up will be mig welding a couple of patches in.
Nice to see the cancer gone.

Fred
 
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