How to Paint Exterior Aluminum

Test the siding for lead paint if you are going to do any washing, sanding or scraping. Purchase a lead paint test kit at a paint or garden supply store. If the old paint contains lead, disturbing it can be hazardous. Contact a lead-abatement professional for advice on how to proceed.

Check for chalking, which is a white powdery coating formed when the paint naturally breaks down. Run a dark rag or your hand over the siding in a sunny spot. If a powdery residue comes off, this must be removed or paint will not adhere.

Scrub or power-wash the aluminum with trisodium phosphate or an exterior siding detergent. If there is mildew present, add one part bleach to three parts of the detergent-water mixture. Do not use bleach with any cleaner containing ammonia, as the mixture creates dangerous chlorine gas.

Prime the aluminum. If it is in good condition, with the chalk completely removed and no bare metal showing, use a high-quality exterior acrylic latex primer. If there is metal showing, or some chalk remaining, use an oil-based primer thinned with about one pint of mineral spirits per gallon of primer.

Paint the aluminum with two coats of pure acrylic latex paint. Apply the paint with brush, roller or sprayer. A sprayer will give the smoothest finish, especially when using a satin or semi-gloss paint.