Tips for Restoring Blackened Cedar Shake Siding

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  • 8-24 hours
  • Beginner
  • 25-750
What You'll Need
Cedar Shakes
Stiff Brush
Eye Protection

Cedar shake siding is considered to be one of the most durable home siding materials. Some homeowners also believe it is one of the more attractive. But unlike other siding, cedar shakes can turn dark and can become quite unattractive and unsightly over a long period of time. This can be especially true in areas of the country where humidity, moisture, and mold are more prevalent. But this material also offers one distinct advantage: with the right cleaning material and information these dark spots can be simply and quickly removed.

1. Clean Surface Dirt

Surface dirt should be removed from cedar shake siding before attempting to remove black spots from the mold. One method that is usually successful is to use a wood cleaning product. Use the directions found on the product's container. The best application method is to use a roller or sprayer to apply the cleaner, then give it 15 minutes to half an hour to soak. Use a stiff brush to loosen any residual dirt and rinse with a hose.

2. Remove Mildew

Mildew and tannin stains are often the causes of dark spots on cedar shakes. But not always. One method used to determine if spots are from these two conditions is to treat them with a solution of bleach (1 part) diluted with water (9 parts). After the bleach solution is applied and the dark spot is scrubbed with a brush and rinsed off, the dark mildew spot will usually disappear almost at once.

3. Remove Tannin Stains

Tannin stains, in contrast to mildew spots that come from outside factors, come naturally from tannin that is inside the cedarwood. Under more natural conditions, the presence of tannin in a tree protects the tree. But in cedar shakes it has the effect of darkening their surface. To treat this condition, the tannin can be neutralized by applying a solution of a wood brightener that contains oxalic acid. This solution is applied to the stains on the cedar shake siding, then is allowed to dry (about ½ hour).

4. Remove Grease Stains

Dark spots on cedar products such as shake siding can sometimes be made by oil or grease that collects dirt and soon becomes dark. These dark stains can be removed by wiping away any excess grease, then dissolving the stain. To remove residual grease or oil, a solution made up of equal parts warm water and white vinegar, when applied repeatedly with a sponge will often work.

5. Remove Black Mold

Black mold can create dark spots on the surface of siding, but often mold growth is not limited to surface areas. If black mold is suspected, it should be inspected by a mold inspector who is certified. If he is unable to detect mold inside your exterior wall but confirms that the dark spot is black mold, the mold should be removed at once. It can most likely be killed by applying a solution of chlorine bleach (1 part) and water (4 parts).