Welding painted metal? Not so fast - Part 1
Welding over paint is not a wise thing to do. In fact, welding and working with previously painted objects is quite problematic, no matter how you look at it. First, it can create noxious fumes and excessive smoke while welding. Many older items have paint full of lead. The temptation is to take a 6010 or 6011 welding rod and just weld right through it, if you are welding with a stick welder, or grab some 70S-6 wire if you are MIG welder and hope for the best in non critical applications.
While it may stick the gases given off won’t be good for you. The second thing is that paint adds impurities to the welds.
Even though you think it is burning off ahead of the arc, once the weld gets up to temperature, the gassing off can get trapped in the weld, along with bits of carbon or other residue. Any way you look at it, taking time to remove the paint is a good idea. Using a safe a proven method to strip paint is important, as residues of remover can create issues as well. It’s common for welders to grind the metal to strip back the paint.
This is quick and it works, but again, if lead is present in the paint or the metal is overheated while grinding, you end up with the same issue of gassing off harmful substances that will be inhaled. It also sends paint specs everywhere, and environmental contamination may be an issue. If this is used, be sure to try to direct grinding dust to a safe area where it can be collected and swept up. And always be sure to use a respirator and safety glasses.