McPherson Quality Painting and Water Proofing

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PROBLEMS & SOLUTIONS

MILDEW

PROBLEM
Mildew is a fungus (mold) that grows on many exterior painted surfaces such as wood, stucco and concrete, as well as on interior bathroom walls. Mildew is not caused by paint. It is a living organism that feeds on other living things, such as wood. Mildew discoloration, which is black or brown and resembles dirt when seen from a distance, is actually caused by fungi feeding on oil contained in paints, or on thickeners in latex coatings. It thrives in warm, humid conditions, and in areas that have little sunlight and poor circulation.

If mildew is not removed from the existing surface and is painted over, it will grow completely through the new coat of paint, even if the paint contains mildewcide.
If it is not corrected, mildew will continue eating away the existing paint, causing eventual paint failure in the affected areas. There is no way to absolutely prevent mildew growth. However, it may be controlled if the proper precautions and recommendations are followed.

Possible causes
Painting over a substrate or coating on which mildew has not
been removed.
Failure to prime a bare wood surface before applying the paint.
Use of a lower-quality alkyd, oil-based or latex paint.

SOLUTION
1.) Determine if the problem area is a mildew problem.
Apply two drops of bleach to the problem area.

If the dark color bleaches out in a few minutes, then it is mildew.
If the dark color persists, it is probably dirt or another type of contamination.

2.) Protect all plants and shrubs with a thin plastic sheeting before cleaning the surface.
3.) Clean the surface with a commercially available mildew remover or use the following solution provided below. The cleaning solution may be applied with a Hudson type sprayer on large areas.

1 gallon of liquid chlorine bleach 3 gallons warm water 1/3 cup of powdered detergent (2/3 cup Tri-Sodium Phosphate may be added for additional cleaning. However, this will leave a residue which requires a thorough double rinsing).

CAUTION:
Chlorine bleach must never be mixed with ammonia or with any detergent or cleaners containing ammonia. These mixtures will form vapors which can be harmful or lethal. Gloves, goggles and protective clothing should be worn for protection.

4.) Rinse surface thoroughly with clean water.
5.) Rinse all plants, shrubs and surrounding surfaces.
6.) Allow the surface to dry.
7.) Prime and paint the surface using the appropriate finishing system.

Most quality paints use mildewcide in all exterior paints to resist new mildew growth. In addition, a fungicide or mildewcide may be added to the primer and paint if extra protection is desired.

 

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Paint Problems and Solutions:
Chalking
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Mildew
Peeling from wood
Surfactant leaching
Tannin staining

Tips for the "do it yourself" consumer:
Quality paint vs.ordinary paint
How to estimate paint quantities
Selecting the right sheen
Window painting made easy
Low Odor Paint Article

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Email: mike@McphersonPainting.com  

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