How to Take Black Marks Off of a Cedar Deck

Cedar decks provide a stable structure because of the strength and durability of the wood, which resists insects such as termites.

Although resistant to rot, cedar wood can fall victim to mold and mildew formation. Mold creates black marks that, over time, lead to a softening of the wood and eventually to wood rot. Removing these black marks regularly -- and preventing them from forming altogether -- helps keep your cedar deck looking like new.

Wet the black spots on your cedar deck with a garden hose, or spray the entire deck to remove dust and dirt.

Mix 1 tsp. liquid dish soap into a gallon of water and mix it well. Dip a stiff-bristle brush into the cleaning solution and scrub the black marks with the soapy brush.

Mix 1 part chlorine bleach with 4 parts water in a clean bucket. Wet a sponge with the solution and apply it to the remaining black marks on your cedar deck. Let the bleach sit on the mold for 10 minutes to kill it.

Rinse the bleach solution from the cedar deck with a garden hose and inspect the black marks. Reapply the bleach solution to any marks that remain. Leave it on for 15 minutes before rinsing it off completely.

Sweep all standing water from the deck after rinsing it, which will help the deck to dry faster.

Things You Will Need

  • Garden hose
  • Liquid dish soap
  • 2 buckets
  • Stiff-bristle brush
  • Bleach
  • Sponge
  • Broom

Tip

  • Remove wet leaves and other debris from cedar decks as soon as possible to reduce black mold marks.

Warning

  • Before applying the bleach solution to all of the marks, test it on a hidden area of the cedar deck to ensure that it won't discolor the wood.

About the Author

Constance Barker, located in the hills of southern Ohio, is the owner and writer of several financial, credit report and travel websites. She started writing in 1999 for private clients and began creating website content in 2004. She gained expertise in home improvement after she and her husband built their home themselves.