Diagnosing and Cleaning Grooved Cedar Shingle Siding

• 1). Test for mildew growth. Most contaminants on cedar siding can be cleaned by wood cleaner and brightener. Mildew is an exception. Mildew can darken cedar wood; but it is also often confused with tannin. Tannin is a naturally-occurring acid common to cedar that can bleed to the surface and cause darkening as well. To test for bleach, place a drop of household bleach onto a dark area of the cedar. If the darkening is caused by mildew, the bleach should clear it almost immediately. If the darkening is caused by tannin or other surface contamination, bleach will have no noticeable affect.
  
  
• 2). If you have bleach, wash the siding with a mild solution of household bleach. Mix 1 part bleach to 3 parts water. Apply the bleach to the siding with a brush or roller and let it sit for about 10 minutes. Then use your nylon scrub brush to remove the mildew. Rinse thoroughly with a garden hose.
  
  
• 3). Clean the siding with a wood cleaner. These cleaners are typically sold in a concentrated form. Follow the manufacturer's instructions regarding the strength of the solution. Apply the wood cleaner to the siding using a paint brush or roller. Let the cleaner sit for 15 minutes. Then scrub the siding down with a nylon scrub brush. Rinse thoroughly with water.
  
  
• 4). Use wood brightener if the wood darkens. Often the process of cleaning natural grooved cedar shingles will cause tannins to rise to the surface and darken the wood. Wood brightener contains oxalic acid, a mild acid that will neutralize the tannins in the wood. Mix the brightener according to the manufacturer's instructions. Apply the brightener with a paint brush or roller. Allow it to sit on the wood for 15 to 30 minutes, then rinse away with water. Don't scrub the wood during brightening.