Paint old aluminum siding by repairing any damaged siding, pressure washing to removing any dirt or debris, applying an oil-based primer, and applying the finish coat. A fresh coat of paint improves the home's curb appeal.
Aluminum siding became popular in the 1950s. Manufacturers sold the material as maintenance-free siding. It does not rot like wood. However, the original paint on most siding is thin and eventually weathers away, sometimes exposing bare metal.
While it is possible to clean small areas and prepare them for paint by hand-washing using a solution of water, trisodium phosphate and bleach, if preparing the entire home, a pressure washer makes the job go faster. It is important to wash the siding from the top down in the direction the rain falls. Washing from the ground with the pressure wand pointing up has the potential of damaging the siding.
Once the siding is clean and dry, apply an oil-based primer. Do not use latex primers. Latex paints contain ammonia, which reacts with the aluminum to form a gas, leaving bubbles under the primer. These bubbles eventually cause the new coat of paint to fail.
After priming the siding, apply the top coat of paint. Latex is acceptable for this coat. The paint retailer can mix the top coat to any color desired.