please spare me . . if you read carefully you will learn. This isn't not the first rodeo as in this is what I do daily, what I taught etc.
yehaadon . . .
Phosphoric acid is available in many places. In automotive paint supplies it will be expensive
surprise, surprise :icon_confused: But you can get it at Home Depot. It is sold as a concrete cleaner. How you use it is critical as well. When you apply it, use a scuff pad. Work it into the pits and other rust. Keep it wet!!!!! Do not let it dry. If it does dry any, re wet and work again with pad. Then when you are satisfied with the results, wipe it dry with paper towels. Phosphoric acid , when dried, will leave a layer on the surface. This is beneficial many times for applications that this acid is used for, but on panels that will be painted, it is not. That is why you need to dry it before it dries itself. Use some gloves as it will burn in small cuts etc. But it's a fairly safe acid to work with. You will find many uses for it. I use it to etch most bare steel before applying the first coat of primer. I also keep some in a container that I drop hardware into. I leave it in a couple days.