How to Properly Paint Rusty Metal

    Without proper surface preparation, rust will continue to cause damage despite the new coat of paint. Fortunately, surface preparation does not always require time-consuming sanding or wire brushing as rust can easily be neutralized with special chemicals that eliminate the most labor-intensive steps of the process. 

    First, any dirt, paint, and loose rust must be removed. Paint can be quickly removed by using a chemical paint stripper, which also has the advantage of avoiding airborne dust particles A handheld wire brush works fine for removing loose rust, but a drill or grinder mounted wire brush makes the job go much faster. 

    Any remaining rust should be relatively hard and dense, this can be treated with a rust converter. Also sold as "rust neutralizer" or "metal prep and etch", these products contain phosphoric acid which converts rust into black iron (III) phosphate which is strong and inert. 

    Rust neutralizers are safe and easy to use, as they can simply be brushed on using a disposable paintbrush. Phosphoric acid is corrosive, so eye protection and gloves are essential. After allowing the chemical to work according to the manufacturer's instructions, any remaining rust neutralizer can simply be wiped off with a rag. 

    After the rust neutralizer does its job, the remaining black phosphate layer can be painted over with any primer suitable for metal surfaces. After the primer dries, the surface can be painted over as usual.