• Defending Exterior Surfaces Against Mildew and Mold

    Published 11/3/2014


    Many homeowners become annoyed when they find those tiny, unsightly spots – black or green, gray or brown – suddenly appearing on the exterior surfaces of their home. The spots are often mistaken for dirt, but hand scrubbing or even pressure washing won’t budge them. So what are they and where did they come from? Whenever your planning vinyl side painting, stucco painting or any kind of exterior painting you want to make sure the surface is clean and ready to paint.

    What you’re seeing is likely mildew (or its cousin, mold). These facts explain the root cause and what to do.

    • Mildew usually grows in a flat pattern that is either powdery or downy. Powdery mildew typically starts out white and may later turn yellow, brown, or black. Downy mildew starts out yellow and later turns brown.
    • Mold is usually fuzzy in appearance and appears as many different colors, including blue, green, yellow, brown, gray, black, or white.
    • Mildew is likely to form on the north side of your house because it remains in shade most of the day and is more likely to remain damp from dew or rain.
    • Paint does not cause mildew. Mildew forms naturally on surfaces that are damp a lot of the time, or on surfaces that receive little or no direct sunlight. Both mildew and mold are a form of fungi, or microscopic plant life.
    • Painting over a contaminated substrate may initially hide those unsightly little spots, but they’ll quickly reappear again (and again) to ruin the beauty of your painted home. Left untreated, mildew will continue to grow right through the new paint film.
    • If mildew or mold is identified and controlled early, painting may not even be necessary. Thoroughly cleaning the surface may effectively remove mildew (and mold) to restore the beauty of your home.

    An Easy Test for Mildew


    To test for mildew, apply a few drops of household bleach to the area. If spots disappear, the discoloration is probably mold or mildew. If they do not disappear, it is probably dirt. While mildew is a common cause of house paint discoloration, many high-quality paints on the market contain a mildewcide to better control outbreaks. Acrylic latex paints also resist mildew better than oil-based paints because latex contains fewer nutrients for the mildew to feed upon. Gloss level also plays a role in mildew growth, since higher gloss paints are less porous, so dirt and mold spores have less to adhere to. And because darker colors dry faster than lighter colors after it rains, darker shades used for exteriors are less receptive to mildew. With these facts in mind, you’ll be better prepared to spot mildew early, before it can get a foothold on your house. And the earlier you spot mildew, the easier it will be to remove.

    Paint colors identified here are from the Sherwin-Williams® color collection.
    For color ideas to enhance any room in your home, contact your local CertaPro Painters®.
    © 2014 CertaPro Painters®
    * As seen in CertaPro Painters® Envision magazine


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