Please watch the attached video that shows the ghost line that can occur through the finished paint with using lapped seams in patch panel/sheet metal repairs. The owner of this wagon did a real nice job on his restoration but when it came time to repair the tailgate rust issues, he chose to do a flange repair. This has been done for a few years, and has seen the hot sun at a few car shows. It's the heating and cooling cycles and the differing expansion and contraction rates between one thickness and two thicknesses of metal adjacent to each other that will cause this "ghost line" to form, showing EXACTLY where the seam is located.

The owner was gracious enough to allow me to film the result of this method that others may see it for themselves and choose another method. A butt welded seam would help to prevent this.

Yes, most of the automakers use flange seams and adhesives in some fashion in today's world, but they DON'T use it where the seam is intended to be invisible across the middle of a panel...... for the exact reason this video shows.

 

Most would argue butt welding, but flange does stiffen the edges lessening likelihood of warping..............