I second that you’re on some sort of residual, thin, rusty spot. They are a pain to stop blow through.
If accessible, a copper backup plate will work wonders for you. I have a chunk of 1” copper pipe that I’ve cut up in various ways. I’ve used it in its original circle 2-3” long, uncurled sections, created little square L shapes, wrapped a flat piece over a dolly, and even put some over a piece of flat bar. The heavy metal acts as heat sink for the weld, the copper prevents sticking, and overall greatly reduces blow through and it also creates a nice flat backed weld that is easier to planish if need be.
They are handy.
Last edited by Fox; Sun Nov 13 2022 05:22 AM.
In the Stovebolt Gallery
]More pictures here
1951 GMC 9430 1 ton dually—-Shiny!
1970 Chevrolet C10 - Grandpa’s- My first truck.—in progress to shiny
1972 Chevrolet C20- Rusty- the puzzle box lid for the C10.
1950 Chevrolet 1300- in progress to shiny.
1962 AMC Rambler American- my wife’s
1951 GMC 9300
1951- Chevrolet 1300