Hiring a professional to paint your aluminum sailboat mast can be very expensive, especially if you have a large sailboat. You can achieve professional-looking results if you paint it yourself, as long as you properly prepare the aluminum for painting and set aside adequate time to complete the job. You can paint over original, professionally applied paint as long as it is not peeling or flaking or you can sand down the original paint to bare metal before applying your new paint.
Remove, or "unstep," the mast and all the hardware from the mast (label the hardware to make reassembly easier). The procedure for removing a sailboat mast varies according to the size, type and age of the mast; if you have never unstepped a mast before, consider receiving help from a worker at your local marina. Anchor your mast to a travel lift at your local marina or a rented crane. Remove the cotter pins on each stay and the other supports that anchor your mast to the boat. Loosen the bolts that fix the mast in the mast step. Raise the mast to remove it from the deck socket. Slowly tilt the mast while keeping the base under firm control and then lower it onto sawhorses or some other type of support.
Note that masts are not extremely heavy themselves but the lever force created by the mast is extremely large and not easily handled.
Sand the existing paint from the mast down to bare metal using 80 grit sandpaper. Use a sanding block or a power sander to sand more uniformly and achieve a better finish later. Never use abrasives containing iron, like steel wool, iron oxide, rouge, or steel wire, as these will corrode the aluminum. Also avoid contact with steel.
Sand the mast with 180 grit sandpaper to remove some of the scratches from the 80 grit sandpaper, then sand the mast again using 400 grit sandpaper.
Clean the mast with water and detergent, then rinse the mast with water.
Spray or brush a chemical conversion coating for aluminum. Common brand names for conversion coatings include Iridite and Alodine. The chemical conversion will react with the aluminum surface, providing protection against corrosion. Spray the coating with fresh water to rinse off the excess.
Spray or brush on two or three thin, light coats of regular primer, primer that binds the substrate and provides mechanical adhesion by settling into scratches on the surface of the mast. Allow the primer to "tack" between coats, or become slightly dry, yet tacky, to the touch. Allow the primer to dry completely after the final application.
Wet-sand the final coat of primer with 600 grit wet-and-dry sandpaper. To wet-sand, wet the sandpaper with water and then sand the surface, wetting the sandpaper when needed. Repeat the process with 800 grit wet-and-dry sandpaper.
Clean the mast with wax and grease remover.
Paint the mast, using two to three coats of paint, allowing the paint to tack between coats. Use marine paint created for use on boats to paint your mast.
To paint over existing paint, sand the current finish with 600 grit sandpaper to scuff the surface, clean with wax and grease remover, then paint with two to three coats.