Most of the rust “converters” like Purple Power, Navel Jelly, and the Eastwood Rust Converter is nothing more than phosphoric acid. It turns ‘iron oxide’ (rust) into ferric phosphate which will create an additional protective barrier for the metal. Spray or brush it on, let it sit for several hours. It is more active when it’s wet so apply additional coats. Once you feel it’s done its job (6+ hrs) rinse it off, let it dry and brush off the heavy ferric phosphate with a course nylon brush. If the scale is heavy it can cause the paint and primer to flake off in that area. I like to spray it on so it can get into areas I can’t reach with a brush. I use a Cornelius keg with a spray wand but you can use a hudson sprayer too. Make sure you wear gloves, long sleeves and eye pro, even though it is nontoxic it is an acid that will irritate your skin. You can get phosphoric acid a lot cheaper than the name brand ‘rust converters’ in bulk if you are treating a large area. I used to buy it at Home Depot in a gallon for <$20.
