What are the reddish brown stains on cedar sidings and trim?
Cedar owes its color and durability to what are called its “extractives.” As moisture passes through the siding, water is being pulled toward the wood’s surface as it evaporates. As this moisture migrates to the surface, it may carry dissolved extractives through the finish leaving a reddish brown deposit. Such discoloration may simply “wash down” with the weather, or may be washed from the surface by using a non-metallic brush and a solution of: two tablespoons of trisodium phosphate (TSP) or other detergent, 1 cup of bleach, and 1 gallon of hot, clean water. Brush on, then rinse thoroughly. Extractive discoloration on the surface finish may occur with either semi-transparent or solid finishes; with either solvent based oil or water-borne latex finishes. Neither extractive discoloration nor mold/mildew growths are the fault of the lumber, the finish or misapplication of a finish. The culprit is excessive moisture and/or improper ventilation. By allowing the moisture to migrate to the
