We have consulted with numerous professionals and organizations with expertise in this field. The general consensus is that mold and mildew do not compromise the structural integrity of lumber, that 99% of the identified fungi are non-allergenic, and that all fungi die once the moisture content of the wood drops below 20%. The structural wood components within a finished home will stabilize at a moisture content well below this level, even if they are exposed to rain and moisture during construction. Mold will grow naturally on almost any organic substance where moisture is present. Mold on lumber and building materials may be present during manufacturing, shipping, or storage. Also, because of our humid environment in Southeast Texas, mold may form during or after installation. Bison Building Materials, LTD., does not control the storage, handling, or use of lumber after jobsite delivery.

The Western Wood Products Association (WWPA) and the Centers for Disease Control (CDC) recommend treating affected areas by spraying a bleach and water mixture. If mold exists in a "closed" building, the affected materials should be allowed to dry and possibly be replaced. We have had several discussions with Houston-area builders, and when mold and/or mildew become an issue, they respond with the aforementioned tactics.

We have created processes that should ensure we will not ship lumber that is blatantly covered with mold and mildew.

We will take the following steps:

1. We will conduct reasonable visual inspections of all incoming shipments of lumber.
2. We will conduct reasonable visual inspections of all shipments to customers and will make every effort not to ship products with obvious signs of mold.
3. We will rotate stock regularly to minimize long-term exposure to the elements.
4. We will pick up any lumber products from a customer's jobsite when both parties agree that there is visible mold, providing that we have been notified within 24 hours of delivery and prior to any use or installation. Lumber returned due to water stains, discoloration, wane, or other non-mold related issues may be subject to a 20% re-stock fee.

The following article from the Western Wood Products Association (WWPA) provides some technical information as to the type of molds in this market.

• It is not uncommon for unseasoned framing lumber to develop surface mold and mildew during transit or storage prior to use. This is especially true during the warm summer months. Surface molds and mildews produce a fuzzy surface growth, which may range in color from yellow to black. These organisms feed off of the sugars and starches readily available in the wood. As the moisture content of the wood drops to below 20%, the growth of these organisms stops. Normally, they do not break down the wood cell wall material and, therefore, cause only cosmetic damage. Stain-causing fungi occur primarily in the sapwood (fiber from the outer region of the tree). Like mold, stain fungi can affect the appearance of lumber but do not cause structural damage to the wood. Blue stain is an example of a cosmetic stain that can readily occur in Poderosa Pine. Although blue stain can be aesthetically pleasing in certain types of applications, lumber manufacturers dry most Ponderosa Pine lumber to prevent its development in their products.

  While mold, mildew and stain do not affect the strength of the wood, their presence does indicate a higher than 20% moisture content level (as in unseasoned wood). This condition can lead to decay if the affected framing lumber is not allowed to dry out. The easiest way to eliminate this possibility is to sticker and stack the lumber or frame the building.

  Air circulation around the affected pieces lowers the surface moisture content level and stops the growth of fungal spores. Lumber seasoned to below the 20% moisture content range rarely, if ever, supports fungal growth. (Source: USDA Agriculture Handbook 72).

  Surface discoloration from mold and mildew on framing lumber can be left on the wood when it is to be covered by a finished wall surface. Proper construction practices will prevent moisture from entering the wall cavity and elevating the moisture content level of the wood.

  For exposed conditions, any discolored wood can be cleaned by using a mixture of one part household bleach to three parts water, sprayed on the wood or applied with a non-metal brush. The wood should be flushed clean afterwards. Commercial mildew removers are also available. As with any cleaning product, wear protective gloves and clothing, avoid skin contact, protect vegetation, and follow manufacturer's safety instructions.

WWPA
522 SW 5th Ave., Suite 500
Portland, OR 97204-2122
Email: info@wwpa.org
Website: http://www.wwpa.org