Normally the flange tool is used first, then the lap weld is performed and filler is used to level it up. The only thing protecting it from moisture is the weld itself.

I'm pretty sure that in pro shops lap welds are only used for glued panels, and the glue does a good job of keeping the moisture out.

If you are actually welding, butt joints are the best, since they require the least amount of filler when all the work is done.


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A lone amateur built the Ark. A large group of professionals built the Titanic.