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Mildew Prevention and Removal

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Often mistaken for dirt buildup, mildew appears as a black, gray, or brown discolouration.

What Is Mildew?

It thrives in moist environments and feeds on organic materials, including the oils in alkyd-based paints and cellulose thickeners found in many latex coatings.

To check whether mildew is present, apply a few drops of household chlorine bleach to an affected area. Mildew will lighten or disappear within a few minutes, while dirt will remain.

Proper Preparation

The best way to control mildew is to prevent it from forming in the first place. A clean, dry, light-filled environment discourages mildew development.

Before you apply any coating, clean and sanitize your surfaces, whether mildew is visible or not. Remember to never paint over mildew–it will grow through new paint, which will make subsequent cleaning and maintenance even more difficult.

Keep decks and wood siding mildew-free by washing it every spring with a cleaner such as our CLEAN (318) multi-purpose cleaner. Also, regularly clean your interior walls with a household bleach solution.

General Care Procedures

If mildew is present, the good news is that your paint has not deteriorated and the mildew can be removed.

Removing Mildew

To remove mildew, follow these steps:

  • Wash a mildewed surface with a mixture of household bleach and water–four parts water to one part bleach–or with a household cleanser designed to kill mildew.
  • Scrub the affected surface with a soft brush.
  • Rinse thoroughly with clean water.

For exterior surfaces, apply the same mixed solution to the effected area and allow it to kill the mildew. This will only take a few minutes. The process can be effectively accomplished using a household garden sprayer. Prior to applying the bleach solution, pre-wet shrubs and plants. After the mildew has lightened in colour or disappeared it must be followed by a heavy rinsing with a garden hose or pressure washed. Pressure cleaning works well with porous surfaces, by removing embedded dirt that could harbor mildew spores.

Preventing Mildew


  • Exterior landscaping should allow for good air circulation and sunlight. Keep shrubs, mulches, plantings, and hanging tree limbs away from your home's exterior walls.
  • Redirect or remove moisture sources that create a mildew-prone environment such as dripping air conditioners, misdirected sprinklers and leaky gutters.
  • Use high quality, mold and mildew resistant products such as our Arborcoat® exterior stain, Regal® Select exterior paint, or Aura® exterior paint.


  • Install ceiling fans, exhaust fans, or dehumidifiers in rooms that are susceptible to mildew growth, such as bathrooms, laundry rooms, and kitchens.
  • Use high quality, mold and mildew resistant products such as our Aura® Bath And Spawaterborne interior paint.

Warning: If you scrape, sand or remove old paint, you may release lead dust. Lead is toxic, and exposure to lead dust can cause serious illness, such as brain damage, especially in children. Pregnant women should also avoid exposure. Wear an approved respirator to control lead exposure. For more information, please visit

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