A.Mac Pearce, an environmental health consultant in St. Paul, Minn., responds: Decay is a process that starts with wood and ends with dirt. Surface mold growth is the beginning of the process. If the wood stays wet enough for long enough, wood rot can set in and destroy the structural integrity of the lumber. By themselves, most molds lack the digestive enzymes needed to penetrate the complex matrix of lignin compounds. Therefore mold growth on framing lumber tends to be confined to the surface, where the colonies feed on wood sugars and cellulose. By aggressively treating the surface, you can render the wood “good as new.”

First scrub the wood with soap and water, then soak it with bleach for 15 minutes before rinsing. The wood can then be sanded and painted with a fungistatic coating. If damp conditions return and persist, mold will grow on the wood, regardless of its past history — but leaving the moldy surface untreated gives the process a head start. Cleaning...

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