Painting a wood garage door is a simple task. A poorly done job, however, will be embarrassingly obvious. Proper preparation before you paint constitutes 99 percent of the work. Inadequate preparation may lead to paint surface failure and, in extreme cases where the door is exposed to continual water, dry rot. If your door has been previously painted, you must strip off any old peeling or blistering paint before applying a new top coat. Use exterior-grade latex paint for a new door or for an old door with old latex paint.
Prepare the Door Surface - Sand the garage door, including any recessed or raised panels. If the door has been previously painted, use a plastic scraper and orbital sander to scrape or sand bumps, ridges, peeling paint or blisters from the old paint.
Apply a thin coat of exterior latex or oil-alkyd primer with a 2-inch natural bristle paintbrush, starting at the top of the door and working your way down. Use a 1-inch paintbrush to work the primer into crevices or routed surfaces in recessed or raised panels. Follow the manufacturer's instructions for drying time. If you used an oil-alkyd primer, soak the paintbrush in mineral spirits to remove the paint and clean the paintbrush.
Paint the recessed or raised panels with the 1-inch and 2-inch paintbrushes. Begin at the top of the door and work your way down. Paint thin coats to prevent drips. Several thin coats are better than few thick coats.
Apply a second coat of paint to the door with the paint roller. Allow the coat the dry completely. Follow the paint manufacturer instructions for drying times and number of coats required.