The two types of finishes traditionally used on guitars are nitro-cellulose lacquer and polyurethane. Most guitar companies use polyurethane. Fender used nitro until the late 1960s and Martin and Gibson still use nitro finishes on their guitars. Nitro finishes and polyurethane both have their advantages and disadvantages. The primary advantage of polyurethane is that it is very strong and durable. However, it dampens the wood, which prevents the guitar from fully resonating. Nitro-cellulose lacquer provides a softer finish that allows the wood grain to breath.
Sand the guitar with 200- to 400-grit sandpaper. Sand in the direction of the grain. The goal is to roughen up the surface so that the paint adheres better to the wood.
Wipe the guitar with a soft tack cloth to remove the dust from the guitar. Vacuum the area so that it is free of dust.
Apply a thin coat of polyester spray paint to the guitar. The polyester paint fills and seals the wood grain of the guitar, which allows the polyurethane top coat to adhere better to the guitar. Paint the front and sides of the guitar. Hold the nozzle of the can eight inches away from the surface of the guitar. Apply a smooth and even coat. Allow the paint to completely dry. Paint the back of the guitar.
Sand the guitar lightly with 400-grit sandpaper. Sand the guitar until it feels smooth to the touch. Wipe the guitar with a soft tack cloth and vacuum the area to remove all the sanding dust
Purchase a polyurethane color or colors for the guitar. Polyurethane guitar paint is available in a variety of colors. If you want a uniformly colored guitar, pick one color. If you want a guitar done in several colors or a sunburst finish, select several colors. Sunburst finishes are created by blending yellow, black and brown colors.
Paint one section of the guitar at a time. If you are using more than one color, tape off sections of guitar with blue painter's tape. This helps to create a straight line or edge between the colors. However, if you want the colors to merge and softly blend into one another where the colors connect, taping is unnecessary. Apply several light coats of paint. Light coats prevent the paint from running or developing heavy edges. Allow each coat to dry before applying the next coat.
Apply a light polyurethane clear coat. The clear coat adds extra protection to the paint and also adds a nice sheen to the guitar finish.