I have used scraps of copper about 1/4" thick, and 1.5" x 3", works great, just clamp it behind the hole or crack.

Copper roofing is to thin, it will melt and fuse with the weld. Needs to have some thickness to dissipate the heat away from the weld immediately, or it melts.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-