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Wood Fungus

Fungus (fungi, plural) is a plant that lacks chlorophyll. Unable to synthesize their own food, they feed off of cells in the wood. The fungi secrete enzymes that break down to wood (into usable food) and can significantly reduce the strength of the wood. It is estimated that Wood-Decay Fungi (found throughout the United States) causes as much, if not more, damage to homes as termites. While the average moisture content of wood is between 13-17 percent, fungus generally occurs when the wood moisture content exceeds 20 percent, coupled with mild temperatures.

Non-Decay Fungi. Sap-staining fungi leave wood with a bluish, bluish-black, gray or brown stain color. Surface-staining fungi (mold and mildew) leave the surface of the wood with a powdery or fuzzy appearance that varies in color. Though sap and surface-staining fungi do not significantly reduce the structural strength of wood, they are considered precursors to wood-decay fungi. White pocket rot produces small pits in wood and is only active in living trees.

Wood-Decay Fungi. White rot leaves wood with a bleached appearance and a spongy and stringy texture. Brown rot leaves wood with a dark brown, checkered appearance and a brittle texture. Note: wood that exhibits brown rot has lost its structural integrity and is easily crumbled. Water-conducing fungus or “dry rot” produces a decay similar to brown rot, but may vary in color.


Proper identification of the type of fungus is essential to developing the proper control measures. Surface-staining fungi can be cleaned with a 50/50 mixture of bleach and water, using a brush or power washer to remove the fungi from the surface of the wood.

For other fungi, the application of Borate wood preservative is a simple and effective control method. Borate is highly toxic to all wood destroying organisms and, unlike other wood preservatives, they are non-volatile, odorless, and are less toxic than table salt. They do not discolor the wood, are non-corrosive, environmentally safe and known to be effective in controlling more than 45 different species of wood decaying fungus. They are also effective in controlling beetles, termites, carpenter ants and a host of other insects.

If the fungi have actually damaged the wood, the corrective action will depend on the severity of the damage. The most effective and common method for moderate to severe damage is to replace the area of damaged wood. However, if only a small area is affected, borates and epoxies are a cost-effective alternative. The rotten wood is excavated and treated with borates. A liquid epoxy consolidant is then applied to harden the soft wood and, once cured, the epoxy wood filler is packed into the void. The surface can then be sanded flush and repainted.

Finally, all reasonable attempts should be made to remove the conditions that allow the growth of fungi, especially moisture. This may include installing a vapor barrier in the crawl spaces, sump pump and dehumidifier in the basement, providing proper drainage of rain and surface water away from the structure, removing sources of water penetration into the structure, and properly ventilating affected areas.