Interior Paint Problems and Solutions – 2

Common Interior Paint Problems and Their Fixes (Part 2 of 5)

Today we continue with the second part of our “Common Interior Paint Problems and Their Fixes” series with part two.

Today’s topic will be Flaking as well as Mildew & Algae.


Has the appearance of severe mildew but will not react to the “bleach test” listed in the Mildew section. Whereas mildew generally has a spotty appearance, darkening and decaying wood generally has a more solid, consistent appearance.

Possible Causes:

Darkening of wood is caused by ultraviolet radiation. This can take place on wood that has never been coated with a protective coating. It also can occur under clear varnishes and lightly pigmented stains. Different degrees of darkening can occur on different woods. If moisture penetrates into the wood, varnish coatings will peel due to wood decomposition under the coating. Woods that are exposed to weather are not protected against wood-destroying organisms. Eventually the wood ceases to be a coatable surface.


New woods must not be exposed to harmful sun rays for extended time periods. If heavily exposed for more that 10 days, the wood should be sanded to a fresh surface before priming. Paint and stain adhesion performance is enhanced when the new wood is painted or stained immediately after installation. Wood that has been allowed to darken (decompose) must be sanded to fresh wood. Wood that cannot be sanded to fresh wood must be replaced.

Coatings can be applied to treated woods after the moisture content has dropped to a paintable level usually 15% or below. Paints, semi-transparent and solid color stains can be used on vertical surfaces or horizontal surfaces.

mildew-algaeMildew & Algae


Black, gray, green or brown areas on the surface of paint or caulk.

Possible Causes:

The appearance of mildew or algae depends on various conditions, which are:

  • Continuously high humidity or dampness. As the humidity increases, mildew growth becomes more rapid.
  • High average temperature.
  • Poor ventilation. Still air increases mildew growth.
  • Composition of surface. Mildew will grow on any surface that provides a nutrient, even dirt.
  • Mildew occurs more often on light colors of paint film. Colors that do not absorb the sun’s heat provide a surface for mildew growth.
  • Cement based products are more prone to support algae growth.


Provide drainage and/or ventilation to remove excess moisture. Wash mildewed areas with Sherwin-Williams ProClean Mildew Remover or a solution of one part household bleach and three parts water. This will destroy mildew and bleach stains caused by mildew growth. Apply solution by brush or a garden sprayer apparatus. Heavy mildew may require additional applications, and scrubbing may be required. Flush area with clean water to remove bleach solution. Allow to dry thoroughly.

Stay tuned for part III where we’ll be discussing Peeling. Don’t miss this one as it will be extremely informative.

If you have any questions, feel free to contact us!

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