The CDC estimates there could be over 300,000 different species of mold and mildew -- different names for the same thing -- worldwide. Many of these are benign, and some, such as Penicillum spp., are beneficial, but most of the species that grow on wood around the home aren't among these. Identifying mold species is beyond most homeowners, but it isn't necessary; you use the same techniques to control all of them.
The Molds on Wood
Mold typically grows on wood that is chronically damp or wet. The moisture may come from inside the wood itself, in which case the mold may have been present when the wood was milled. When the moisture comes from the environment in the form of condensation, humidity, a plumbing leak or rainfall, the most troublesome types of molds, such as Stachybotrys, Aspergillus and Fusarium can grow. More benign types also may grow on the surface of wood in conditions of high humidity. These powdery mold colonies are often identified as mildew, but they are also types of mold.
The first step in mold remediation is to control the moisture that feeds the colony. If mold grows inside a wall and becomes visible on wet drywall, it's a sign of a plumbing, roofing or siding leak that needs attention. When wooden outdoor furniture gets moldy, it's often because it's been standing on bare ground, and moisture has wicked into the legs from the ground. Move furniture into the sun and set it on dry ground. Mildew deposits on indoor wooden furniture are often a sign of high humidity. To control mold, the CDC recommends keeping your indoor humidity below 50 percent. Even if you do this, you may need to provide better ventilation.
Clean Mold with Soapy Water
Once you have a handle on moisture, the next step is to remove all the visible mold from the affected piece or area of wood. Use detergent and water for this -- not bleach; bleach kills visible mold, but it doesn't penetrate wood to kill the roots, and it's corrosive and can damage most furniture finishes. Wipe away all visible mold with the detergent solution, using a rough cloth and changing the cleaning solution whenever it gets blackened. You may need a scrub brush to remove all of the mold. Wear a mask while cleaning to protect yourself from inhaling any of the spores. You should also wear gloves and protective clothing.
Physically removing mold isn't the whole story -- to prevent mold from growing back, you need to ensure the wood stays dry, and you should disinfect it. Of the many commercial products available, the ones used most often by hospitals contain neutral-pH salts called quaternary ammonium chlorides, or quats. They kill a broad spectrum of bacteria and viruses as well as mold, and they are safe for most wood finishes. Full-strength vinegar also disinfects, but it doesn't provide lasting protection. Borate-based disinfectants, on the other hand, do penetrate wood grain and remain there to prevent mold spores from sprouting. A simple homemade disinfectant spray for exterior wood, wood framing and other unfinished surfaces includes a cup of vinegar and a cup of boric acid in a gallon of water.