This was a job I was working on last year for the City of Des Moines' City Hall...This entire job was TIG welded using straight Argon as a sheilding gas and a Thoriated Tungsten electrode. I can't recall the alloy of the filler rod. Using the TIG process made this job difficult due to the high composition of Zinc in Alloy 385. With a composition of 40%, the Zinc would quickly burn and collect within the puddle. A soft start would almost immediately contaminate the weld. With a beveled butt-joint, the heat was cranked and the pedal was put to the floorboard. No more than an inch bead was likely to be run due to the zinc. Absolutely ANY debris would mess these welds up. When/if attempting, have a stainless steel brush handy at all time.