Cleaning and Removing Mildew from Exterior Walls and Siding

Mildew is unsightly but easy to remove. Moisture, and therefore mildew, can be controlled to a degree by arranging landscaping so that natural breezes can flow near the houseand dry the siding if it becomes wet from rain or dew. Keep shrubs awayfrom the walls. Gutters and downspouts, as well as a moderate roofoverhang, will help also. Give special attention to air movementpatterns on northern exposures where sunlight cannot assist in drying.On sidings which may have a tendency to absorb moisture from rain ordew, a semi-gloss or gloss latex or oil paint with an appropriateprimer is recommended. When wood siding is stained or left to weathernaturally, use a water-repellent (often combined with a woodpreservative) finish. These products are available in hardware/paintstores. To remove mildew from siding, follow these steps:   WOOD SIDING, HARDI-PLANK or STUCCO Use the following solution:

  • 1/3 cup all-purpose laundry detergent
  • 1 quart household chlorine bleach (must be fresh)
  • 3 quarts warm water
  • An alkaline cleaner such as washing soda or a cleaner containing trisodium phosphate can be added for extra cleaning. Follow package directions or use ½ to 2/3 cup.

Scrub the surface with a soft brush. Avoid splashing on shrubs and other plants. Rinse well. Commercial mildew remover/cleaners are also available. Do wear protective clothing – long sleeves, goggles, rubber gloves. If your siding needs to be repainted, choose a mildew-resistant paint. The most mildew susceptible paints are latex paints, especially when linseed oil base primer is used. Acrylic gloss and semi-gloss latex paints are less susceptible to mildew than flat latex. Linseed oil base paints are also very susceptible. The least susceptible paints are exterior enamels. Special paints are available that contain a mildewcide.   BRICK Once a year spray your brick off with the hose and a spray nozzle. A solution of one cup of bleach mixed with a gallon of water can be used with a stiff brush to clean this off. Don’t use wire brushes or synthetic brushes–they can discolor the brick–use a natural fiber brush. Soak the brick before washing with the bleach solution.   STONE To clean stone walls, fences or other structures, wash with a mild soap solution. Rinse well with clean water.