[Moneyguy1]

Extend (and I am not a chemist) evidently turns Fe2O3 to Fe3O4, or black rust. It is water soluable, so it has to be finish coated with something else, like a good enamel. I used a lot of it on cars I towed out of barns back in the 80s to preserve the bodywork. Very rarely did I have a body panel rust through if it was wire brushed, cleaned, "Extended" and then sealed with (inside only) Rustoleum. Outside body work I sealed with the Extend, then standard automotive primer, and automotive finishes.