Undercoating/Primers

A friend had recommended to me that whenever i expose sheet metal (taking paint off or just getting into the frame rails, etc) that i use ohpso (spelling?). I can't seem to find anything about this product online but he said it acts as a rust converter and looks a little like wood stain. Does anyone have any ideas on what product he may be referring to?

Thanks  

Rob, the product your friend is talking about is Ospho Rust Remover. It is a zinc rich product. The zinc is the key. It is a rust inhibitor. Instead of the corrosion attacking the metal, it attaches the zinc first. I would suggest removing all the rust. Sanding, grinding, sand blasting or what ever is available. Then wash the surface with a metal conditioner such as PPG's DX579. Then prime with a quality epoxy primer. Some people elect to prime with an etch primer and not use the acid metal wash. This is an OK system too. I prefer the acid and epoxy system myself. A little more work, but in the long run, a better system.  
Mustang enthusiast since 1973.

I HAVE USED OSPHO FOR MANY YEARS. IT IS VERY STRONG PHOSPHORIC ACID THAT TURNS RUST BLACK. IT DRIES SLOWLY. A MILDER FORM OF THIS IS DX 520 MADE BY PPG. IF YOU GO ON THE PPG WEBSITE YOU WILL SEE THAT THEY DO NOT RECOMMEND USING THIS ACID TREATMENT BEFORE PAINTING WITH ETCH PRIMERS OR ON BARE METAL WHERE PLASTIC FILLER WILL BE APPLIED.or .
I HAVE USED OSPHO SUCCESSFULLY FOLLOWED BY ENAMEL OR LACQUER PAINTS.IT STOPS RUST VERY WELL.