"Direct to metal" paint, also called DTM paint, is used for a variety of interior and exterior surfaces. Paints labeled for DTM usage are available at most hardware stores and some automotive supply stores. DTM paint is usually made with acrylic resin, and it is formulated for use on unprimed metal. Because you don't need to worry about primer, using DTM paint is faster than painting with a traditional acrylic paint. For good DTM coverage, however, you still need to do some light prep work and use the proper tools for application.
Things You'll Need
Airless spray gun
Scrape off large rust spots with a wire brush. DTM paint helps seal metal surfaces for better rust protection, but existing rust spots need to be removed first.
Scrub off smaller rust deposits with a scouring pad.
Wash the surface with soap, water and a rag. Dirty surfaces don't accept DTM paint easily.
Lay plastic sheets and painter's tape over nearby items. DTM paint is best applied with an airless sprayer, and the sprayer's mist can accidentally blow onto adjacent surfaces.
Spray DTM paint onto the surface with an airless spray gun. Hold the nozzle 12 to 14 inches from the surface for best results. Keep the nozzle moving, and work in parallel strokes.
Remove the painter's tape after the DTM paint has dried for 24 hours.