Not having any rear access to a repair, in thin metal, in a critical area, is challenging. Here are some areas with no access to back-up a blow thru. The tailgate edge was not possible for me to slide hammer. Too stiff in that area. The tailgate was extremely dented in a deep karate chop crease and associated long dent. 2 places. A "long" and a "short" section. You can see the 1" thick bondo chunk I took out. Sitting on the gate top, white/pink thing. I cut out the dented roll edge section in such a way as to be able to reach in and also straighten out the flat portion. Then work the removed crease/dent piece back to round. I also created an inner backing edge all around the opening. You can see the start of this in one pic (black paint not removed yet) and see the plug welds into this "inner skeleton backer" on the other tacked-on long patch. I can not afford to take a chance and blow thru when almost done, then chase a blow out. When you grind a blow out bridge it sometimes opens up again. Talk about going crazy!!!
I'm just not going to fight that anymore on no-access panels. Now I will always add a plug welded backer plate. It's Bartamosity not to.
Maybe some of this will help someone who is frustrated like I was. It all worked very well. As you can see, the process of cutting out a badly creased area and use that piece as the patch, leaves some funky wide gaps. That's another good reason for a backer. You could make a whole new patch but it was easier to get the cutout pieces to fit. You should always consider fixing the dent by removing it and pounding it back to shape, It's faster, if you can believe it. It's already the right size
Don't be temped to use a .040 thick angle grinder disc. It will shatter and hurt you. Tried that already. Use 1/16 and keep the cut as thin as possible with that. You can use a .045 3" die grinder disc. That's pretty safe. Less likely to break because less flex, less leverage. Nice thin cut for my reweld scenario.
None of the tailgate is finish welded yet. I'm outside in very high heat and can only work 2 hrs and rest inside. I use cold towels on my head when not welding. Drink lots of water. It is really hot. Unpainted metal in the shade is too hot to touch.
