Surface Preparation
If mildew is already present on a substrate, the mildew but be killed and removed before the substrate is finished, or else the mildew will grow through the new coating. To kill mildew and remove mildew from the surface, follow the steps outlined below:
1. Using a spray canister(one designed for insecticide application will do) available at most hardware stores, apply the following solution liberally to the substrate and allow to set for about 10-15 minutes:
a. 3 quarts water
b. One quart common household bleach
c. 1/4 cup maximum of liquid dishwasher detergent (ammonia-free)
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The bleach is the key component that actually kills the mildew. Allowing this solution to set for five minutes give the bleach time to settle into any crevices and hard to reach place to kill all the mildew present. Skipping this 10-15 minute set time may result in an inadequate job. The detergent is added in a small amount to help emulsify any mildew or dirt to aid in its removal. Liquid dishwasher detergent is the best choice it will not foam like regular dish or laundry detergent.
2. Using the same solution, wash the substrate clean using a power washer. A Second choice if a power washer is unavailable is to scrub the surface with the same solution. Far masonry substrates use a wire brush. For wood, use a softer bristle brush. And for substrates sensitive to abrasive damage like aluminium and vinyl siding, use a sponge.
If mildew was present on the original substrate or previous coats, and a new finish coat is already applied, the mildew will grow through the coating. It is usually impossible to stop mildew growth at this point. All the coatings must be stripped down to the original substrate and then cleaned as described above before applied a new coat. (7)
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