I have vinyl siding with black mold on it. Should I power wash it, or is there a simpler solution?



Without seeing your home, we suspect the moldy sections of your vinyl siding are on a part of the house that gets little or no direct sunlight, and the wind does not circulate freely around these moldy spots. Any surface that stays moist will grow mold. This is exactly like moss growing on the north side of trees in a forest because the sunlight never shines on the north side of a tree.

Power washing should only be done by those who have solid experience with the equipment. If the nozzle is held at the wrong angle, it can push water behind the siding or dent the finish. Some vinyl manufacturers’ warranties specifically don’t cover power washing mishaps. This is why we discourage power washing as a DIY activity.

To gently but effectively clean your vinyl siding, we suggest this 2-step method. Start with a mixture of 1/3 cup of powdered laundry detergent to 1 gallon of water, and scrub with a push broom or broom head on a long paint pole. Start from the bottom and work your way up the siding. Rinse off thoroughly with a garden hose. This should remove the mold spots and surface dirt.

Next, make a light solution of 3 quarts bleach, 1 quart of either Jomax or Simple Green and 4 gallons water.  Apply with the same brush method, and again starting from the bottom and working up. But this time, leave the mixture to dry on the siding – no rinsing necessary. The residue will wash off with the first rain, but will protect the surface a little bit longer.

Just like washing your car, regular cleaning of siding helps keep the dust and pollen from building up on the surface. Dust and pollen holds moisture and promotes mold and mildew growth. Regularly washing your siding – especially the problem areas – will keep the mold at bay.

Please be careful with the bleach and Simple Green mixture. Wear rubber gloves and eye protection, and protect nearby vegetation with tarps. Also be aware that wood composite (like TREX) decks with a deep color pigment may be affected by the bleach. We also need to highlight again that power washing is best left to professionals.

Mosby offers siding services, including vinyl siding maintenance and installation. We can also help with your cleaning and mold needs. If you’d like our help with your siding, call the Mosby Building Arts office at 314.909.1800 or contact us here.

And for more answers to common home maintenance questions, visit our Home Improvement Library.