Old aluminum siding can shine once again

By Gene Gary, Copley News Service

Q. Our house is partially covered with aluminum siding which was installed during the late l970s. The siding is in very good condition, except that it develops a white powder after it rains. The powder coats the windows and discolors the brick below the siding. The siding finish appears to be an enamel that was applied at the factory. We would like to get rid of the powdering effect and give the siding a fresh coat of paint. What is the best way to clean and eliminate the powdering effect and paint the aluminum siding?

A. Once cleaned, you may or may not want to paint your siding. Even siding with a finish that is oxidized or "chalking" at the surface can often be restored to a good appearance if the proper cleaning methods are used. Keep in mind that new paint will also get dirty, and there are other possible problems such as peeling and flaking of the new paint (which is not a problem with the baked-on factory finish). You may want to save yourself the expense and effort of painting, unless a color change is important.

Regardless, the first step is to give your siding a thorough cleaning. In order to paint, the aluminum must be completely free of dirt, grease, oil and as much chalking as possible. Professionals use a power washer. You can rent one for the task. Be sure and follow the manufacturer's directions carefully and take care not to spray directly at windows, electric outlets, vents or electric lines. Keep the nozzle at least 12 inches away from the surface, and be careful not to spray upward at the siding. The powerful water spray could loosen or damage it, and result in moisture getting trapped underneath.

Another method of cleaning recommended by some siding manufacturers is to use a soft-bristle brush, such as an auto-washing brush and a solution of regular household detergent. Rinse thoroughly with clean water from a garden hose. A more potent formula would be to mix 1/3 cup powdered detergent with 2/3 cup TSP (trisodium phosphate -- purchased from a paint dealer) and 1 quart liquid laundry bleach all combined with 3 quarts water. Some home centers also sell special aluminum-siding cleaners containing heavy-duty detergents. Specific directions for those should be followed carefully according to the literature provided by the manufacturer.

You may need to remove any remaining chalky residue using a steel wool substitute, such as a 3M finishing pad. Do not use steel wool or a wire brush, which can leave metal fragments to rust on your siding.

Once the siding is clean, you can decide whether to paint or not. Do keep in mind that the chalking will return and cleaning the exterior siding is a periodic chore. However, once painted, the aluminum siding (like any other painted surface) will have to be repainted periodically.

If you decide to paint, invest in paints that are specifically made for metal siding. You will need both a primer and a paint. You will probably have to make this purchase at a well-stocked paint store or home center. Metal Siding Refinish marketed by Pittsburgh Paints is a good choice. It comes in a variety of colors. This is a latex paint that dries to a low-luster eggshell sheen, much like the finish on new siding. It's a urethane-modified acrylic paint that produces a harder, more durable finish than ordinary house paint.

Other manufacturers of paints specifically formulated for metal siding include Fuller-O'Brien, Benjamin Moore and Devoe & Reynolds. Your local paint dealer should be able to help you select a quality paint and recommended a primer that will last a long time.

If your siding is pitted or dented, you can use a flat finish paint to help hide the imperfections, but an eggshell or satin finish is the best choice for longevity and durability. Pick a light color rather than a darker shade. Dark colors absorb more heat from the sun and can cause vinyl siding panels to buckle.

Spend the extra money to invest in top-quality paints. The finish will last longer and resist common paint problems such as peeling, blistering and flaking. With proper application, your aluminum paint job should last six to eight years depending on climatic conditions.

Send e-mail to copleysd@copleynews.com or write to Here's How, Copley News Service, P.O. Box 120190, San Diego, CA 92112-0191. Only questions of general interest can be answered in the column.