While Quality Aluminum products resist most common household stains like oil and grease, it will become dirty like any other product that is exposed to atmospheric conditions. Chalk may also accumulate on the surface; a normal condition for all pigmented materials which are constantly exposed to sunlight and the elements. However, soil, grime and chalk can be simply removed with the help of your garden hose and a bucket of soapy water.
Stubborn stains If especially stubborn stains cannot be removed with normal household detergents, request a cleaner from your siding contractor. Always test an cleaner on an inconspicious area before full use.
Mildew Mildew may be a problem in some areas. it appears as black spots on surface dirt and is usually first detected in areas not subjected to rainfall, such as under eaves and porch enclosures.
  For removal, prepare a solution as follows:
  1/3 cup detergent (Tide for example)
  2/3 cup Trisodium Phosphate (Soilax for example)
  1 quart 5% Sodium Hypochlorite ( Chlorx for examaple)
  3 quarts water
  CAUTION: Greater concentration may cause damage to the finish

If the above solution does not readily remove the mildew spots, request a mildew type cleaner from your contractor.