Before fungi can colonize wood, four requirements must be met: an oxygen supply, temperature in the 40° to 100° F range, a supply of sufficient moisture, and a food source (wood). Eliminating any one of the necessary requirements can prevent infection. Since controlling temperature, oxygen and the food source is nearly impossible you must control the source of moisture.
Fungus takes many different forms. When detected early, treatments may be possible that will prevent further decay damage and save expensive repairs. When fungus is ignored wood replacement is usually necessary, along with stopping the source of water.
The most effective "method" of preventing fungal deterioration of wood is to keep it dry. Most fungi need a wood moisture content of at least 20%. Eliminating the moisture source will stop the growth of fungus but the spores will remain viable. Boron ( disodium octaborate tetrahydrate) will kill existing fungus and eliminate future infestations. Boron is water diffusible so it will actually use the elevated moisture to pull the boron deep into the wood. Borates defuse through wood drawing into the highest points of moisture leaving behind the residue, which fills the cellular structure of the wood with the chemical, thus preventing decay fungi and infestations of other wood destroying pests.
Dealing With Decay
The first and most important thing to do once decay is discovered is to figure out where the water is coming from. Check for the obvious - roof and plumbing leaks, and missing or punctured flashing. Are there any sprinklers allowing water to hit the exterior walls? Are eaves wide enough to prevent water from cascading down sidewalls? Are gutters poorly maintained or missing? Do finish grades slope towards or away from the foundation? Are foundation cracks admitting water? Is untreated wood in direct contact with concrete, masonry, or soil? Check to see if crawl spaces have soil covers, and if venting and/or insulation are present, adequate, and properly placed. The same goes for attics. Peeling and blistering paint often signal inadequate ventilation, or a missing vapor barrier. A moisture meter may be necessary in many instances to identify areas of elevated moisture that may otherwise go undetected by visual inspection alone.
Water stains on framing and sheathing inside walls may be evidence of condensation. Moisture build-up in wall cavities can go undetected by visual inspections alone. Repairs should be permanent not a band-aid. You've got to cure the problem, water infiltration, not just treat symptoms such as mildew or decay. Once the source of water has been stopped, remove as much decayed wood as is practical and economical. This is especially important with girders, columns, and other critical members whose load-carrying ability may have been compromised. Cut back rotted members to sound wood. When a partially decayed structural member can't be replaced, reinforce it with a "sister" anchored to sound wood. Decayed wood absorbs and holds water more readily than sound wood. Let rotted areas of members not removed dry out before making repairs and closing in.
Types of fungus
Decay fungi fall into three major groups: brown rots, white rots, and soft rots. The latter are rarely found inside homes, though they occasionally degrade wood shakes and shingles on heavily shaded roofs.
Surface molds and mildew - These are not decay fungi and can be controlled by correcting the excessive moisture and cleaning them off with a mildew removal product.
Stain fungus - Often called "blue stain or sap stain" this shows as a blue or green discoloring of the wood, and even demands a higher price when the wood is sold in lumber yards. While these fungi are feeding on the wood, they do so at such a slow rate that it is not considered a decay concern.
Pocket Rot - This obvious effect shows as small white cavities formed throughout a piece of wood. This fungus grows only in the tree while still standing, but often exists in milled lumber that is then built into a structure. It is not a decay fungus and generally does not indicate the continued presence of moisture. Pocket rot does not attack cut wood, therefore no treatment is necessary.
Soft Rot - This is a decay fungus that rarely is found in structures, although wood shake roofs that are heavily shaded in wet climates may be subject to its attack.
White Rot - These decay fungi attack hardwoods only, working very slowly in their consumption of the wood. They feed on both the cellulose of the wood cells as well as the lignin, the glue that holds wood together. The result of attack by white rot is wood with a white, spongy look. While it certainly has harmed the wood it works so slowly that it is uncommon in structures. In its initial stages of attack this fungus leaves thin black lines along the advancing line of the fungus.
Brown Rot - Brown rots, attacking primarily softwoods, that are the biggest concern for structural wood integrity. They feed only on the cellulose and they work very quickly, leaving the wood with a dark brown coloration.
Poria Incrassata - Poria has an appetite not only for common construction woods such as oak and pine, but for cedar, redwood, cypress and juniper that are naturally decay-resistant. In addition to attacking most woods classed as naturally decay resistant, laboratory tests show that poria is resistant to many fungicides containing copper. Poria is one of the most destructive fungal species homeowners may ever encounter.
In-place treatment with borates
Dormant fungi can be reactivated when dry, infected wood is rewetted. Consider treating infected, but otherwise serviceable wood left in place with boron liquid or boron foam that will not only kill active fungi, but also guard against future infection. Borates have low toxicity to humans and are even approved for interior use in food processing plants. Boron doesn't affect wood's strength; color, or finishing ability. Boron doesn’t corrode fasteners, and doesn’t outgas vapors. Widely used in treating new timbers for log homes, they're the preservative of choice for remedial treatment of wood in service. Because of the decay hazard posed whenever wood is in contact with concrete or soil, concentrated diffusible boron is often inserted into holes bored near contact areas.
MORE ON Fungus Control
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