I also second POR-15 with a note. Do not wire wheel the rust off before hand. If you want to knock it down, sand it with some 80 grit and blow away. If you wire wheel it, it will peel off in sheets because the wire wheel polishes the steel smooth. The POR needs that rough surface to bind to. If it gets a good base, it is nearly impossible to get off.
Don’t get it on your hands, or your students will be asking you to wash your hands for the next 2 weeks at least.
