Originally Posted by Kevin316
Should a flange seam be used whenever possible? Do you do anything to the back side to seal it so water doesn't get in and sit there?
I have read elsewhere that a but joint is the favored method.
It all depends Kevin they both have they're advantages,but the only way a flange joint will hold water is if it done upside down...The original panel has to be flanged not the new piece the open edge of the joint is facing down then when your done welding you seam seal the whole back side of the seam...
On a long seam I prefere a flange because its stronger and straighter when done needing little to no dolly work...as long as you prepped the flange so its not wavey ,if its wavey when you start it'll be wavey when you finish.
Butt joints are more likely to warp a panel but since the joint doesnt have the two layers its not as strong and can be hammered and dollied back into shape when it warps (and it WILL warp) another advantage of a butt is it can be dressed up on the inside and wont be noticed, a flanged joint is obvious from inside the trunk ....So you really need to know how to do both so you can decide which one is best for your applicationbut even a flanged joint has butts at the endsIts alot harder to make a proper flange joint but easier to weld butts are way easier to make but harder to weld.I do both ,but on long seams I do a lot more flanges than butts...