Today I used some body solder to attempt to fill in the low spots remaining in the passenger-side door dent. Yesterday I did my best to pull out the dent with a slide hammer and then shrink the sheet metal back semi-close to flush. Here are the pictures of what it looked like afterwards.
My first step was to clean off the dent area to remove the coating left by the Metal Prep I sprayed on and any leftover debris left from the welding and subsequent grinding of welds. I used a 3M Clean and Strip wheel. BTW, those 3M wheels are fantastic for removing paint and cleaning metal without damaging it, but don’t by the ones with a plastic shaft because they will break right off if you try to use them in a drill.
Then I wiped the entire area down with acetone to remove any grease.
The first step in applying body solder is to put on the tinning compound, which binds to the steel and also binds to the solder. The solder itself would not adequately bond to bare steel, so the tin is a necessary intermediate step.
I bought a Lead-Free Body Solder kit from the Eastwood Company; that kit included everything I needed such as tinning compound, a brass brush to apply it, the rods of solder, a wooden paddle to shape the solder after it goes on, some paddle lube to prevent the wood from sticking to the solder, and a nice file to shape body repairs. I went with the lead-free solder because, unlike the lead which was used in the old days for body repairs, this solder can be sanded without releasing particles that would be harmful to breath.
I began by stirring up the tinning compound, and then brushing it onto the door.
After the surface was coated, I began to heat the tin using a small propane torch I bought at Home Depot.
As the tin began to melt, it turned shiny silver and brown impurities moved to the edges. I wiped the hot tin across the surface of the steel with a clean white cotton shop towel.
I moved across the surface of the door heating the tin until it liquefied and then wiping it across, until the entire surface was coated in tinning compound.
Then I washed down the tinning compound, which apparently is somewhat acidic, using warm water until the rag I was using came up clean.
Then I started applying the solder. I used the same propane torch, heating the door and the end of the rod of solder and depositing globs of solder onto the door. Eventually the rod got short enough that it was getting very hot, so I dropped the remaining two inches or so straight into the repair.
Then I used the wooden paddle to try to spread the solder out more flat over the low spots in the door. It was a very inexact way to shape the solder.
Here is a look at the profile of the solder repair.
I worked the solder with the file that came with the kit, which was only marginally useful, so I also used some 80-grit sandpaper to shape the repair. It came into a bit better shape, though far from perfect.