Watch this video from This Old House to learn how to paint aluminum siding.
1. Rub siding with cloth to check for powdery paint pigment and mildew.
2. Cover ground and nearby shrubs with drop cloths.
3. Test old siding paint for lead using a lead test kit; if lead is present, contact a licensed lead abatement specialist.
4. Don gloves, then mix in a bucket a cleaning solution of one cup chlorine bleach, one cup TSP and one gallon of water.
5. Soak abrasive sponge in cleaning solution and scrub siding clean.
6. Rinse siding with garden hose.
7. For large areas, use a pressure washer to spray cleaning solution onto siding.
8. Connect garden hose to pressure washer and attach a fan-spray tip to the washer's wand.
9. Fill the washer's reservoir with bleach/TSP/water cleaning solution.
10. Aim the spray tip at an angle to the surface, pointing downward to avoid shooting water under the siding.
11. Rinse the siding with clean water.
12. Let siding dry, then apply one coat of acrylic primer followed by two coats of acrylic topcoat paint.
13. Remove drop cloths after painting.