i used rust bullit instead of por15 and i think it works better. you can put it over old paint and rusted metal just the usal wire brushing to get rid of the loose paint and rust. The navy uses this stuff on there boats and they say it outlast por15. there are two typs though industral and auto motive the automotive is what i used it sprayed right on with a hvlp spray gun http://www.rustbullet.com/