Originally Posted by roach711
Phosphoric acid is less aggressive to both metal and skin (you still don't want it splashed on you). It converts the rust into iron phosphate that acts as a good base for primer and paint. Ospho is a popular brand name but most paint shops have it under their own brand name, usually "metal prep", "rust converter" or something similar.
Will this stuff get into the spaces between two rusted beams and convert that rust too? There is a shuttle that exactly fits my needs except the beams under the floor and the frame members in the body are pretty damned rusty. I am willing to remove the floor and interior walls to sand-blast most of the rust off the frame and the beams. However, I am very concerned that the rust between the frame and the exterior skin, as well as the rust between the transverse beams and the main, longitudinal beams would continue to fester.