Ospho, good or bad?

I have searched and found you guys using ospho to kill the rust. I have por15 and the advise to use a metal prep, ospho, to clean the metal. I put this all over the underside of my tub and washed it off per instructions. On another forum, Autobody101.com, some say epoxy primer might not stick to the ospho coating. What now?

Im only putting the por-15 over the rust not the entire floor because of problems with por15 lifting if not on rust.

Thanks, Dan

 

I have found ospho to be almost useless.

Permatex makes a rust converter that is about 10 bucks a bottle. It seems to work very well.