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How to kill green mold on an outside wall

Updated February 21, 2019

Mold may appear on the outside of your home's walls if they are consistently damp due to rain, excessive shade or high humidity. Green mould may be indicative of Cladosporium, Aspergillus or Penicillium mould. Not only does mould look unsightly, but it can eat away at your paint and damage it while releasing potentially hazardous spores into the air. Kill green mould on your wall to eliminate these cosmetic, structural and respiratory risks.

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  1. Shoot down the wall with a pressure washer's fan spray. Use smooth, even strokes to cover the entirety of the wall, not just the area on which you notice mould growth. This forcefully removes most of the mould spores from your wall's paint and crevices. If you don't have a pressure washer, use a garden hose with a sprayer attachment to rinse the wall as best you can.

  2. Create a mould-killing solution. Pour a gallon of warm water into a plastic bucket. Mix in 1/2 cup of household bleach and 1/4 cup of standard powdered laundry detergent. Stir thoroughly. Mix in 1/2 cup of trisodium phosphate, a cleaning agent available at many hardware stores.

  3. Sponge the solution onto the green mould growth. If the mould growth is widespread, you may wish to use a garden sprayer, such as the type used to spray herbicides or liquid fertilisers. Allow the solution to soak on the wall for 15 minutes, during which time the bleach will sterilise the surface and kill the mould.

  4. Scrub the wall with a sponge. While the mould may be dead, some staining and mould growth may still be visible. The trisodium phosphate and laundry detergent will help loosen any mould stains.

  5. Rinse the wall by shooting it down with a water hose. Let the wall dry thoroughly, which may take 24 hours or more depending on your climate.

  6. Tip

    Consider repainting the wall with a mould-inhibiting paint after cleaning it. This can help control and prevent future mould growth.

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Things You'll Need

  • Pressure washer
  • Water hose
  • Bucket
  • Household bleach
  • Powdered laundry detergent
  • Trisodium phosphate
  • Sponge
  • Garden sprayer

About the Author

Joshua Duvauchelle

Joshua Duvauchelle is a certified personal trainer and health journalist, relationships expert and gardening specialist. His articles and advice have appeared in dozens of magazines, including exercise workouts in Shape, relationship guides for Alive and lifestyle tips for Lifehacker. In his spare time, he enjoys yoga and urban patio gardening.

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