Things You'll Need
Latex or rubber gloves
If the stain won't come off, bring a sample of the aluminum siding to a paint store, and have them match the color and sheen so you can paint over the stains. You should be able to gently pry off a corner piece of siding, then nail it back after you have the paint.
Don't be tempted to use paint or stain stripper to remove dried deck stain from aluminum siding. Chemical strippers designed to remove dried deck stain will also remove paint from the siding.
Deck stain is thin, so it splashes and spatters easily, making it challenging to do a really neat job. Unfortunately, it's all too easy to get deck stain on your aluminum siding while staining your deck. Your success in removing deck stain from aluminum siding will depend on how fresh the stain is, and whether the siding has the factory finish or has been repainted. If all else fails, you can match the siding color and repaint the stained parts of the siding.
Put on a pair of latex or rubber gloves. Saturate a rag with mineral spirits. Scrub at the stain, turning and rewetting the rag frequently. If it is oil-based deck stain applied within a day or so, mineral spirits should remove it.
Mix strong detergent, such as trisodium phosphate (TSP), with warm water in a plastic bucket. Proportions vary according to the type of detergent. A heaping tablespoonful of TSP added to a quart of water effectively cleans many stains.
Test the detergent on a hidden corner of the siding to make sure it doesn't remove the finish. The factory paint applied to aluminum siding is usually designed to "chalk," or gradually wear away. If the siding is older, scrubbing it may quickly wear it down to bare metal.
Scrub the stain using a soft-bristled brush and the detergent mixture. This is most likely to work if the deck stain was latex or water-based.
Clean the entire length of the affected siding boards, otherwise you risk having clean spots surrounded by grimy siding. This won't be so obvious if you clean the entire board.
Rinse the siding with a hose and cold water.
Stevie Donald has been an online writer since 2004, producing articles for numerous websites and magazines. Her writing chops include three books on dog care and training, one of which won a prestigious national award in 2003. Donald has also been a painting contractor since 1979, painting interiors and exteriors.