How to Remove Flagstone Mildew

Updated February 21, 2017

Flagstone is a term used to describe flat rocks that are commonly used in landscape design. Constantly exposed to elements, the beautiful stones are subject to all that Mother Nature has to offer, such as mould and mildew. Mildew is the unfortunate byproduct of mould. It leaves a light layer of black and white on anything it touches, and in addition to being more than unsightly, it can put off an odour. Cleaning mildew off flagstone is a simple process that can return the stones to their natural beauty in no time.

Choose either bleach or vinegar. Bleach is very effective but can be harmful to nearby plants and foliage. Vinegar is an eco-friendly alternative to bleach.

Mix a solution of equal parts water and bleach in a spray bottle. Or put full-strength vinegar in the spray bottle. Do NOT mix bleach and vinegar.

Spray the mildewed area with the solution and allow it to sit for at least 15 minutes.

Scrub the area with a soft bristle brush to remove all of the mildew.

Rinse the area by spraying the stones with a garden hose to remove the debris.

Allow the stones to dry in the sunshine.


Test the stones for colour fastness by applying bleach to an indiscreet area of the stone before using it to clean the entire area.

Things You'll Need

  • Bleach
  • Vinegar
  • Spray bottle
  • Soft bristle brush
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