Yeah I get you now, that "black carbon" looks like a spray on rubberised stone chip spray to be honest. 2k FFS!! The annoying thing is we are all paying for this in our insurance premium.
Thanks the car was put away dry in June into my dry heated garage so I'd assume it's bone dry, the spatter your referring to I'd assume that I wouldn't see? As it would be inside the box section as the rust "pings" off from the heat?. The rusty sections were cut out until I hit decent steel new...
Bloke walking past with his dog reckoned any rust on the back of the metal will come back through the weld from behind making the weld "bubbly and porous" ?
As already said it looks like seam sealer and (Iam no expert far from it) looks like it's the original seam sealer, when I hit a rock that a nieghbour had put there to stop people parking on thier verge,( that'll learn me!) I put a severe dint in my sill of my old Astra van, my mate at the body...
Currently welding my old Land Rover chassis, which is rusting from the inside, if you can't clean the back of the metal easily and only clean up the front surface where you are welding will the poor rear surface affect the weld? Thanks.
It passed the mot with the repair :) just to pick up on this point made by David 2015, it's really hard to see from the photo that I took,the bit you've highlighted far right is where the underseal had lifted, the Elongated "c" shape you've highlighted at the front was seam welded from above...
It's on the footwell of my E36 BMW, there's a bit on the far right that looks as if it hasn't joined the metal, but it just a line where the underseal has lifted, Iam not making excuses but I really struggled to get comfy, couldn't see where I was welding as well as I'd of liked and blew through...