If the metal shed in the back yard is starting to look shabby, a new coat of paint could restore it to its initial luster and help prevent rust from corroding the walls. Though painting a metal building may seem like an ominous task, it isn't very different from painting a wood building. With some extra care in your prep work, painting will be easy and last for many years.
Prepare your surface. Remove mildew by applying a mixture of 3 parts water to 1 part bleach. Remove loose paint or rust by scraping the affected areas with a wire brush. Finish by washing the whole building with soapy water or use a power washer with water. Let it completely dry.
Apply two coats of primer with a paint sprayer or use brushes or rollers, following the manufacturer's directions on drying time. Use a primer suitable for metal. You only need to apply primer if the old paint comes off in a powdery form when wiped with your finger, or if the building has never been painted.
Paint the building after the coats of primer are completely dry. Acrylic latex house paint suitable for painting on metal is recommended unless the previous coats of paint were oil-based. If the paint on the building was an oil-based paint, you must use oil-based primer and paint.