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Mold spores can be found almost anywhere; they can grow on virtually any substance, provided moisture is present. There are more than 100,000 species of mold, and at least 1,000 varieties are common in the U.S., according to the New York City Department of Health. Mold is most likely to grow where there is water or dampness, such as in bathrooms and basements.
Mold can occur naturally on lumber under certain conditions, normally due to the presence of moisture in or on the wood, and warm temperatures. Molds are
fungi; ubiquitous organisms that (under proper conditions) can grow on organic matter. Surface molds, which can come from a variety of sources including airborne spores, feed off the sugars and starches readily available in wood.
Jump to the info you want by clicking a link below:
• Moisture & Conditions for Wood Decay
• Fast Facts About Lumber & Mold
• Stopping Mold: Prevention from Mill to Builder
• Mold Prevention Tips for the Homeowner
• Mold Prevention Tips for the Homebuyer
• Mold Removal and Remediation
• Health Effects Associated with Mold
• Links to More Information
• Download Lumber Tip Sheet: Managing Moisture
& Mold
Moisture and Conditions for Wood Decay
When unprotected wood is exposed to the elements, excessive moisture, or contact with the ground, it is susceptible to decay. Four conditions are required for decay to occur: moisture, favorable temperature (approx. 50 to 90 degrees Fahrenheit), oxygen, and a source of food (wood fiber). If any of these four conditions is removed decay or infestation will not occur. Mold requires moisture to survive, so protecting lumber and wood structures from moisture will prevent mold growth and decay.
Wood Moisture Content (MC) and Decay Conditions:
- Optimum decay condition, MC 25%+
- Marginal decay condition, MC 20 - 25%
- No decay, MC 20% or less
Fast Facts on Lumber and Mold
- Discoloration aside, molds generally have little effect on the structural integrity of framing lumber.
- Mold needs a moisture content (MC) of at least 20% to survive on wood.
- Southern Pine dimensional lumber is typically kiln-dried to maximum 19% MC or less. The moisture content will be identified on the grade stamp.
Stopping Mold: Prevention from Mill to Builder
When properly kiln dried to 19% or less moisture content, Southern Pine dimension lumber will not support the growth of mold. Unfortunately, lumber can be exposed to adverse weather or moisture during shipment, storage, or the construction process before final installation. Protecting lumber from moisture to prevent the growth of mold requires vigilance and teamwork by all parties in the chain of custody.
Manufacturer Role
- The Southern Pine manufacturer should provide the customer with a dimension lumber product that is properly dried to a moisture content of 19% or less and properly grade marked.
- The manufacturer should insure proper binding, handling and storage of lumber at the mill site.
- At the purchaser's request, the manufacturer should properly wrap the lumber and order the shipment covered with a tarp during transport.
- At the purchaser's request, the manufacturer should add a mold inhibitor to pressure-treated lumber. If intended for use in an enclosed structure, it is recommended that pressure-treated lumber be specified kiln dried after treatment (KDAT) to a moisture content of 19% or less.
Purchaser and Transporter Role
- Wrapping and shipping options are chosen at the purchaser's discretion. The purchaser may choose not to wrap the shipment, or may choose what is usually a paper wrap that covers each unit (lumber on five sides) or individual pieces (glulam on all six sides). Method of shipment is also a purchaser choice. Most wood products ship from the manufacturer on either open rail cars or flatbed trucks. For shipment on flatbed trucks, the purchaser may also choose to order a cover, usually a full tarpaulin, to increase the level of protection.
- The transporter is responsible for proper handling and timely delivery of the shipment. If requested by the purchaser, it is the transporter's responsibility to cover the lumber with a tarp and maintain that cover from pickup to delivery.
Receiving Facility Role
- The condition of the lumber should be checked immediately upon delivery to the receiving facility.
- Storing lumber under cover in an open shed or a climate-controlled facility would be ideal, but not common practice. If stored outdoors, it is suggested that lumber be pre-ordered with a plastic or paper wrap, or covered with a vapor permeable tarp. Lumber packs need to be properly bunked underneath (4x4s are recommended) to separate the material from ground contact.
- Storage time should be kept to a minimum in order to reduce exposure to moisture and the elements.
The Builder's Role
- The builder should check the condition of the lumber immediately upon delivery to the site.
- On the building site, lumber should be stored in an orderly fashion and protected from moisture. Again, lumber packs need to be properly bunked underneath (4x4s are recommended) to separate the material from ground contact. Keep lumber covered with a tarp or other vapor-permeable cover.
- Practice good housekeeping and segregate scraps from the lumber storage area. Scraps scattered about on moist ground is food for mold.
- Once the builder is assured that all framing lumber is dried to a moisture content of 19% or less, the structure should be enclosed as soon as possible. Purchase of a moisture meter might be a good investment.
Blue Stain is not Mold
- Blue stain is not mold. Blue stain, or sap stain, is a bluish or grayish black discoloration of the sapwood caused by the growth of certain dark-colored fungi on the surface and interior of the wood. Blue stain can occur under the same conditions that favor the growth of other fungi.
- With some molds and the lesser fungus stains, there is no clear-cut way to differentiate between the two. In general, however, the difference between mold and stain is made primarily on the basis of the depth of discoloration. Unlike mold fungus, typical sap stain or blue stain fungus penetrates deeply into the sapwood and cannot be removed by surfacing or chemical cleaners.
- Under Southern Pine Inspection Bureau grading rules, stain, and discoloration due to exposure to the elements, are characteristics allowed on Southern Pine lumber. Stain is an appearance characteristic only and is allowed in varying degrees in all lumber grades. It does not affect lumber strength or utility, nor does it pose any health risk.
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