I'm currently in the middle of replacing the front section of the roof skin on my W150. I'm going back and forth on the idea of welding it in or using the 3m 8115 panel bonding adhesive. It's only the skin, nothing structural. I've always just welded patch panels in, however, my concern is that after I weld the roof skin patch panel in, I won't be able to access the underside of the roof skin to treat it and protect it from rusting out again in a couple of years. I know they make weld through primers, but I want to make sure that this is the only time that I have to make this repair. I've never used the 3m adhesive before. If I did go this route, how far of an overlap should there be on the two pieces of sheet metal? Any opinions on the 3m adhesives? Thanks

i panel bond a lot
i should say weld/ bond because now we use a squeeze type welder and weld thru the glue when it's wet.

the panel overlaps are the same as welding.
grind the flanges being bonded with 36 grit to give the glue something more to grab on to.
and there is a newer glue, impact bonding adhesive that has a little more shear strength.

both glues use a special applicator to use them.
yes it's possible to mix the glue up like body filler. doing so is asking for some big problems if you do this. i would strongly recommend against trying this.

impact bond

3M has a pretty good tech section on how to use their stuff. In some cases it's not designed to completely replaced welding, but work in conjunction with it. I'd start looking there.

Here's a LINK to get you started.

ok. thanks