How to Clean Green Mold Off an Outside Painted Deck

Since your painted deck is outside in the wind, rain, and extreme temperatures, it can develop problems that must be taken care of as soon as possible to keep the deck looking its best. Green mould is a common problem that develops on decks when they are left damp for long periods. The green mould can stain and damage your deck. When removing green mould, care must be taken not to harm the deck or the paint covering the deck.

Rinse the painted deck with a water hose. Use pressure from the water to remove surface dirt and debris.

Put on a pair of rubber gloves. This will prevent any skin irritation that may be caused by the cleaning chemicals.

Fill a 5-gallon bucket with 1 gallon of lukewarm water. Add 1/2 cup of TSP -- trisodium phosphate -- and 2 drops of liquid dish soap. Alternatively, replace the TSP with 1/2 cup of bleach.

Saturate a stiff-bristled brush broom in the mixture. Begin scrubbing the painted deck with the brush broom. Start at the area farthest from the entrance, and work toward it.

Continue saturating the brush broom in the mixture and scrubbing the deck until you have thoroughly cleaned the deck and removed the green mould.

Rinse the deck clean with the water hose. Allow the deck to air-dry.

Sweep the painted deck regularly to remove dirt, debris, and decaying vegetation -- such as leaves -- that can trap moisture against the wood and cause mould to grow on the deck.


Trisodium phosphate -- also known as TSP -- is a heavy duty cleaner that kills mould. It is available at home improvement stores.


Never mix bleach with ammonia or products containing ammonia. The resulting fumes are toxic.

Things You'll Need

  • Water hose
  • Rubber gloves
  • 5-gallon bucket
  • Trisodium phosphate
  • Liquid dish soap
  • Stiff-bristled brush broom
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About the Author

Amanda Flanigan began writing professionally in 2007. Flanigan has written for various publications, including WV Living and American Craft Council, and has published several eBooks on craft and garden-related subjects. Flanigan completed two writing courses at Pierpont Community and Technical College.