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; 11/13/2022 5:22 AM.
