How to Clean Algae Off a Cedar Deck


The natural beauty and fine, even grain of cedar makes it an attractive wood for backyard decks. In addition to its good looks, cedar naturally resists water, which makes it a good choice in regions with high humidity. But despite its durability, cedar is still susceptible to mold, mildew and algae damage, often caused by wet, decomposing leaves in the fall and winter.

Things You'll Need

  • Broom
  • Latex gloves
  • Safety glasses
  • Household liquid bleach
  • Bucket
  • Heavy-duty scrub brush
  • Garden hose
  • Sweep the surface of the cedar deck to remove dirt, leaves and twigs. Clear out any debris trapped between the planks as well. Relocate deck furniture.

  • Put on latex gloves and safety glasses to protect your hands and eyes from the bleach. Mix one part of a liquid household bleach in a bucket with three parts warm water.

  • Dip a heavy-duty scrub brush in the bleach-and-water mixture and begin scrubbing the algae off the cedar wood. Work your way from one side of the deck to the other, scrubbing the entire surface as you repeatedly soak the brush.

  • Allow the bleach to remain on the deck for 15 minutes. Use a garden hose to completely rinse the solution off the wood. Allow the deck to dry thoroughly before placing items back onto it.

Tips & Warnings

  • Consider sealing your cedar deck after it dries completely to prevent algae from growing on the surface in the future.
  • A strong bleach solution can kill grass and other vegetation. Cover all plantings in and around your work area with plastic tarps or sheeting.
  • Avoid using a pressure washer when cleaning your cedar deck, as the force can cause water to penetrate and damage the soft wood.

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