Ospho advice.

HI,

Ospho is basically a phosphoric acid solution. It converts iron oxide (rust) into iron phosphate which is more chemically stable that rust. The bigger concern with phosphoric acid compounds is that not all primers are compatible with it and you need to be sure it is properly neutralized and removed. I think if you flush the ospho with plenty of clean water and not let it dry on the metal surface you will be okay with the weld through primer. I don't think you will have any issues with welding the treated metal although usually you would weld first then treat the metal with the acid.