Hugh Cairns: Grey spots on siding
Aug 19, 2013 / 5:00 am
Q. I have noticed that I have small grey spots on two sides of the vinyl sidings of our house. Can you please tell me what they are and how to get rid of them? – Many thanks, Norm
A. You bet. Untested, we can’t say with absolute certainty what the organic composition of the grey spots is, but experience indicates that it is likely mold or mildew growth. Often mistaken for dirt at the beginning, mold or mildew growth can colonize on your siding. Rapidly starting off as small black, brown or grey spots, they can lead to larger patches of discoloration. Untreated, mold and mildew growth will darken and expand.
Conditions have to be right for mold and mildew growth. I see it on the sides of homes where condensation or moisture conditions are prevalent. Sometimes I see this growth on siding in shaded areas, under the eaves or behind vegetation against the structure. I also find it on gutters and downspouts given their nature as being obvious conduits of water.
The vinyl siding installed on your home can be prone to mold or mildew growth because the surface is rough and bumpy and can hold low levels of moisture for a long time.
Norm, in any event you’ll want to clean your siding and most likely you’ll approach the clean as though the observed material is organic. There are several ready-made commercial cleaners available on the market to treat the affected areas. I usually ignore them and go to the time tested combination of bleach, tri-sodium phosphate and water. Use the same amount of bleach that tri-sodium phosphate producers recommend with water. Whatever you do, don’t clean just the affected area; you’ll want to clean the whole wall. Carefully scrub with a soft brush and rinse well and repeat.
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