Rust not only looks unsightly, it is corrosive. If you leave it untreated, it can ruin the metal surface on which it is oxidizing. You can inhibit rust growth by painting the metal; but before you do this, you should take steps to eliminate as much of the oxidized metal as you can. Sanding is an effective way to do this, but it isn't always practical. When it isn't, there are alternative methods for removing the rust that are just as effective. Treat the surface to inhibit further rust growth before you paint it.
Things You'll Need
Medium to coarse steel wool
Chemical rust remover
Air spray gun
Scrub the rusted surface with a wire brush, working the bristles into corners that you can't reach with sandpaper. If the bristles clog, clean them with mineral spirits or lacquer thinner rather than with water.
Vigorously rub down the surface with medium to coarse steel wool. It is not as aggressive as a wire brush and presents less danger of scratching the metal surface. Soak it periodically with mineral spirits or lacquer thinner to keep it clean and lubricated.
Wash the surface with water, let it dry, then spray on a chemical rust remover after first diluting the chemical rust remover according to the specifications on the container. Spray it with a power washer on large surfaces, like metal roofs, or with a hand sprayer on small surfaces. Let it work for the time recommended by the manufacturer, then wash it off with water.
Spread a rust inhibitor onto the rusted areas after they have dried. There are many types, and they work by either sealing the rust in or providing a coating that reacts with oxygen to prevent rust. You can spray it on with an air sprayer or paint it with a paintbrush.
Prime the rusted surface with a high-quality metal primer before you paint it. Primer adheres better to metal than paint does and provides an extra layer of protection against further rusting. You can spray primer with an air spray gun or paint it with a paintbrush.
Chemicals that remove rust are either highly alkaline or acid. Either way, they are hazardous and should be handled with care.