I'm in the process of mig-welding in some rust repair patches. (That spot aft of the rear wheel arches, where innner fender, outer wheel arch, rear quarter panel, and spare-wheel well all come together is really cute!) Because I'm still learning to handle the welder, I'm sticking to the less visible, inside bits for the moment. The results are nothing to brag about, but I think I'm improving - I hope.
Question: There is caulking in the joints where the flanges of the panels are spot-welded together. Caulking between panels that are bolted together, like the inner and outer front fenders, makes sense. Actually, caulking between welded panels does too, but how do they manage to spot-weld the two pieces of sheet metal together through the insulating layer of caulking? Do industrial spot welders apply so much pressure at the spot to be welded that the caulking is squeezed out and conductivity is re-established? Can anyone clear up this mystery for me? I can't even get a decent tack weld unless both pieces of metal are shiny clean!
Bob S.