When it comes to painting smooth, non-porous metallic surfaces, certain preparation steps must be performed to avoid problems with paint adhesion. Complicating the process is the fact that different types of metal require different application strategies. Surfaces like brass, steel and aluminum all require different preparation standards to promote paint adhesion. If you are planning to paint cast aluminum, you need to know the proper types of materials to use and the correct application techniques in which to apply them or you may run into problems.
Clean any slimy or greasy areas of the cast aluminum using a chemical degreaser.
Clean the aluminum thoroughly using a pressure washer. Use a water hose en lieu of a pressure washer if the aluminum is thin and could easily be damaged by forceful water pressure.
Apply blue painter's tape to all areas you want to protect from primer or paint.
Apply the zinc chromate-based primer to the cast aluminum using the 3 to 4-inch oil-based paintbrush. Do not over-apply or you may end up with runs and drips. Allow the primer to dry for at least two hours.
Clean the paintbrush at least three times with mineral spirits. Massage the mineral spirits into the bristles of the brush using your bare hands.
Apply oil-based paint to the cast aluminum in the same manner as you did the primer in Step 4. Allow the paint to dry for at least two hours. Apply additional coats as necessary.