Care and Maintenance
The surfaces of finished Western Red Cedar decking, and siding and trim boards exposed outdoors inevitably become dirty and can also be discolored by mildew, algae and moss. These natural elements slowly erode the finishes and as a result, all finishes applied to cedar require regular cleaning and maintenance to perform. The degree of maintenance depends on local climatic conditions, the type of finish and end use (deck or siding).
Dirt – Dirt is the most benign cause of discoloration. A periodic cleaning with a mild, non-phosphate detergent solution will usually restore the surface finish.
Mildew – Mildew is a common form of discoloration of paints and stains caused by staining fungi. Restaining does not solve a mildew problem. When it is time to refinish, clean off the mildew with a mild bleach solution (oxygen bleach is preferred) or commercial mildew-remover. After the wood has been thoroughly rinsed and allowed to dry, refinish with a coating that contains an effective mildewcide.
Tip: A simple test for the presence of mildew on the coating can be made by applying a drop or two of a fresh solution of liquid household bleach (containing 5 percent sodium hypochlorite) to the stained area. The dark color of mildew will usually bleach out in 15 to 30 seconds. Discoloration that does not bleach is due to other factors and requires further investigation.
Extractives Bleeding – Discoloration due to extractive bleeding is usually caused by moisture. To stop stains caused by extractive bleeding, the moisture source must be eliminated. Mild staining is often washed away by rain over a period of weeks. In sheltered areas of a building where the stain persists, it may become darker with age and more difficult to remove. If washing with a mild detergent solution does not work, applying a mild oxalic acid solution has been proven to be effective in removing water, tannin or iron stains. Commercial cleaners are also available. If the stain remains, prime the area with an alkyd primer and top coat with a latex coating.