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One much-touted feature of aluminum factory coatings is their "self cleaning" property. This means that the paint is designed to slowly wear down. The surface of the paint slowly turns into powder, washing gradually off the house and revealing the clean underlying paint, much like a snake sloughing its old skin. Run your hand over the surface of the aluminum siding. If a residue of powdery material comes off, this is called chalking and must be removed. Paint will not adhere to a chalky surface. Check all sides of your house---chalking will be most evident on the south or sunny side.
Look for mildew. If you're unsure whether the black discoloration is mold or dirt, spray some bleach on it. If it quickly turns light brown, then disappears, it's mildew. -
Remove chalk and dirt with a scouring pad or scrub brush (look for one that can be attached to an extension pole) and household detergent. If there's mildew present, use exterior siding detergent with added mildewcide. Rinse thoroughly with a hose. Aluminum houses can be power washed, but hire a professional if you've never done this before. It's easy to damage or dislodge the siding with the wrong technique.
Don't use spackle to fill holes because it's too brittle. Aluminum siding flexes with temperature changes, so fill holes and gaps with paintable silicone caulking. Fill large holes, dents or other extensive damage with auto-body filler, or cover them with aluminum patches.
Unless the aluminum siding was in almost-new condition, with little or no chalking or fading, it will have to be primed. Don't use a water-based primer because it won't adhere well. Use an exterior oil-based primer formulated for aluminum siding. The primer can be thinned with mineral spirits--formulas differ, so check the label for thinning directions. -
Use 100 percent acrylic exterior paint over the primer. Do two coats for the best appearance and durability. Aluminum siding can get hot in direct sunlight, so choosing a lighter color will not only extend the life of your paint job, it can reduce cooing costs in summer. Generally, flat or eggshell finishes look better on aluminum because higher glosses accentuate surface irregularities and imperfections.
You can paint aluminum siding with a roller, brush or spray. Spraying is faster, but you will have to use masking paper and tape to protect windows and other architectural elements that aren't being painted. You can rent airless sprayers at most home and equipment rental stores. If using a brush or roller, purchase the best quality you can afford. Good brushes and rollers hold more paint, apply it more evenly and make the job faster and cleaner.
Whatever method you choose, start painting at the top of the siding and work down. If using a roller, do all your cutting in (painting the edges with a brush) before rolling, to minimize brush marks. Protect trim with blue painter's tape, and remove it as soon as you've finished painting so it doesn't bake on to the surface.
Avoid painting in the hot sun because the hot aluminum will gum up your paint and cause an uneven finish. Plan your day's work so you can follow the shade around the house. Using a paint conditioner (see Resources) can improve the final appearance of the paint, and makes it easier to work with.
