Clean metal is CLEAN METAL. Its a prerequisite for welding period. So, what I do in this very situation is sandblast the area. You can get guns that blast local areas well without too much fallout. Or use 36 grit discs until you get to shiny metal. In any case, if its not very shiny metal, you aren't done. John is right of course, its more about metallurgy and whats best practice. Lots of people LOVE POR 15. That's great and all, but its not mainstream, so if there is fallout like this, start with clean metal and now we have come full circle!
