Auto body repair & detailing: rust repair, rust repair, butt welding

Question
I have an 88 mustang gt. The roof section where the roof meets the hatch has rusted through about 2" wide and 20" long starting fom the drivers side to about the center of the roof. I took the roof from a donor mustang and have cut out the section I need. I drilled out all spotwelds and  seam solder to keep the old panel as complete as possible. Now I have to install it in the good mustang. Should I but weld it or flange the sheet metal and lap weld?? Also, can the the flange tool be used on panels that have a arc to them already? Should I flange the original roof or can I flange the donor section?? What are you doin' saturday? Wanna weld it in for me? I'll buy the beers!!! thanks  TJ

Answer
Hey TJ! Use the panel flanger and lap weld the seam, It will work fine on an arked panel. Flange the origional panel, I.E. the car's roof. The flange will give the panel a little more strength, and the extra little bit of sheet metal will give heat somewhere to go. Butt welding is a really horrible way to go, especially if you ever have seen a butt welded sheet metal joint from the back. It's all chicken shitty, with molten globs of metal and pieces of weld wire sticking up everywhere like little antennas. I think that will cause rust a lot quicker than a properly done lap weld.  I would just zap it with tack welds, or VERY small stitch welds, like a half inch. Bounce around, only do a couple or three zaps at a time- don't let the panel heat up. Heat will move around the new piece, and distort the sheet metal. Now, Expect some warpage. One thing you can do to combat heat warpage is to get some Play-doh, mix a little water into it, and put it around the area you are welding. It will act as a heat sink. I wish you had emailed me before you cut the donor roof- I would have tried to talk you into replacing the entire skin, and just gluing it on with panel adhesive. It's really no more work than patching the panel and using filler over it. I suppose that ship has sailed, what you are doing is fine. It just sounds like you have it well within your grasp to skin a roof. I'd come over and help you weld her up today, but my sister is comin' over. It's the whole holiday thing. Drink a beer for me, make mine a Miller's. Happy holidays from NW Ohio. Bill