After leaving aluminium piping outdoors for several days, you may notice a spotty white residue coating the metal. This is known as white rust, which is a type of corrosion found on surfaces that have been galvanised, or coated in a protective layer of zinc. Once moisture begins to react with the zinc, patches of white rust begin to form. White rust is soft and powdery to the touch, making its removal quite simple.
Wet the rusted area with water. Remove light patches of white rust by rubbing the area with #0000 steel wool. Rinse clean and blot the surface dry with a towel.
Apply a commercial rust remover to the surface for heavier patches of rust. Allow the solution to penetrate the rust for 10 to 20 minutes. You may use distilled vinegar as an alternative.
Scrub the surface vigorously using a wire brush. Wipe the surface clean to check your progress. If rust remains, repeat Steps 2 and 3.
Rinse the surface completely and blot dry with a towel.
Prevent formation of white rust by storing your aluminium items in a dry area. Pack aluminium items so that air can circulate freely. If storing piping, stand it upright to allow any water to drain.
You can apply water-repellent wax coatings to aluminium to protect the metal from moisture. You'll find these coatings at any home improvement or hardware store.