welding .010 aluminum (roof flashing mat'l)

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I tried welding pretty thin (.010) aluminum, the kind that roofers use for flashing. I could get a real nice bead on a flat piece, but when I tried to do a lap weld, the top piece's edge would melt away enough so that I'd have to chase it, and the weld would suffer. I put a weight on top of the two pieces to hold them together.... I think maybe using thoriated tungsten (.040)may be my problem (all I had at the time). I cleaned the metal with a ss wire brush, then wiped it with acetone b/4 welding. I'm using a squarewave 175 set pretty low and controllable...Any suggestions?
Reply:You might want to try folding the top piece's end over onto it self and smash it real flat before you put the two pieces together.  This way you're welding on the outside of the bend rather than the end of the metal.
Reply:I tried that, and it was better, but  I wanted to  to achieve a decent weld the hard way (personal challenge) figuring that it is doable by using the correct technique..... always looking for that correct technique!
Reply:You can also try holding your tig torch straight up and down, and point the tungsten directly at the top piece, that way you are seeing both thicknesses instead of one, as thin as these are the weld will flow down to the bottom piece, just remember to concentrate the bulk of your heat on the thicker side of the joint. Good Luck!