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| Lumber Mold Review |
Introduction
If you walk into a retail lumber store or a lumber yard, you will notice a variety of scattered discoloration on almost every piece
of lumber. Lumber mold is found on many construction materials as a result of being exposed to high humidity for extended
periods of time during construction too.
Lumber is an excellent source of nutrition for fungal growth. Wood is primarily composed of cellulose and lignin. It also contains
sugars, starches, proteins, lipids, and fatty acids. Even after a tree is harvested, all of these materials remain in the wood and
provide a food source for fungi. Prior to harvesting, the bark of the tree serves as a protective skin. It is when the bark is
removed that the tree is susceptible to mold growth.
Fungi can grow naturally on lumber under certain conditions. Moisture content above 20 percent for a week is required for
fungal growth on lumber and wood structures.
This review article is about the molds that can grow in lumber yards and at building construction sites. Based on the ability to
penetrate the lumber wood tissue, these fungi are grouped into two main groups, (i) sap stain fungi and (ii) surface fungi.
Sap Stain Fungi
Sap stain fungi affects the sapwood of lumber. Sap stain fungi utilizes sugars, starches, proteins and fats stored in the sap wood
tissue as nutrients. Sap stain fungi cause discoloration of wood tissue by their darkly pigmented mycelia, spores, and melanin
produced by the fungi. Sap stains appear as gray, black or bluish discolorations of the sapwood.
A very common example of sap stain fungi is the Ceratocystis/Ophistoma group which appears on framing lumber and which is
more commonly knows as "blue stain". This is found on lumber as it arrives from the lumber yard, a condition that is readily
apparent to a building expert and which can be confirmed by sample identification.
The most prevalent fungi in stored logs and lumber are those which affect mainly the sapwood, and the resulting damage is
called "sap stain". It causes objectionable discoloration and darkening of the wood. In most cases, the strength of the wood is not
affected. However, where heavy sap stain is prevalent, the toughness of the wood or its ability to withstand shock may be
reduced. The difference between sap stain fungi and surface fungi is the depth of discoloration. Typical sap stain penetrates
deeply into the sapwood and cannot be removed by surfacing or chemical cleaners. The damage to the wood from lumber mold
is cosmetic only, not structural.
Surface Fungi
Molds do not discolor wood as deeply as sap stain fungi. In most situations, surface mold growth is a superficial phenomenon
that does not affect the strength or long-term durability of the wood. Mold gives a fuzzy and powdery appearance of various
colors including gray, black, brown, green and white.
Most of these fungi, however, are commonly found as airborne fungal spores in our environment that subsequently set on
surfaces of wood. When the environmental conditions are suitable, spores will grow and cause wood discoloration.
Some fungal species, including species of Acremonium, Alternaria, Aspergillus, Cladosporium, Paecilomyces, Penicillium, Mucor, Phoma,
and Trichoderma, can grow on the surface of freshly cut wood. These fungi utilize the carbohydrates (e.g., sugar, starch) in the
wood as a source of nutrients. The surface mold causes discoloration of the wood surface by their pigmented spores and/or
mycelia, but they generally do not damage the wood structure.
The way to distinguish between sap stain and surface fungi is to lightly rub the surface of the wood that shows discoloration.
Surface fungi can be brushed off or smeared and removed, whereas sap stain fungi is not removable due to their deep
penetration in the wood.
Fungal Growth Requirements
Four conditions are required for fungal growth to occur on lumber:
1. Moisture (over 20%)
2. Favorable temperature (Approx. 50-90 degrees Fahrenheit)
3. Oxygen
4. A source of food (wood fibers)
If any of these four conditions is removed, fungal growth or infestation will not occur. Mold requires moisture to survive, so
protecting lumber and wood structures from moisture will prevent mold growth.
Health Effects
There is no scientific evidence that lumber mold poses a health hazard. However, mold may be allergenic, as is typical of fungi in
general. If so, the persons at greatest risk are lumber yard workers or carpenters, but no reference is made in the literature to
these occupations being at risk. In addition, no risk has been documented for occupants of homes built with wood containing
Ceratocystis/Ophistoma. Individuals who have mold allergies or suppressed immune systems (such as may be the case for those
receiving treatment for cancer or HIV), have a greater likelihood of reacting to the presence of mold. However, once lumber
mold is encased within a wall system, there is little chance of exposure and as such, ill health is unlikely. Clearly, mold from
outdoors entering a home through opened windows or doors is a far greater source of indoor mold.
Framing lumber in a newly finished house is typically encased by panels or siding on the outside and drywall or panels on the
inside. As such, there is virtually no chance for occupants in a home to be exposed to any mold on the wood through skin contact
or ingestion.
Inhalation exposure to mold on framing lumber in a finished home is possible,but not very likely. Mycotoxins are not volatile, so
they cannot "off-gas" into the environment or migrate through walls or floors independent of a particle. Since particles cannot
move through solid objects, mycotoxins in molds contained inside a wall or floor cavity will stay there unless disturbed.
A California family recently negotiated a landmark 22.6 million dollar settlement in a toxic mold case, claiming that moldy lumber
used to build their house created a "poison prison" that severely injured their son.
Mold Contamination of Newly Built and Under Construction Houses
Newly built and under construction houses could be mold contaminated even before the new homeowner moves in. There are
the following possibilities for mold contamination:
Prevention of Mold During New Home Construction
As a summary, the key for preventing moldy lumber is to purchase dry wood and keep it dry. Store wood properly by keeping
it off the ground, away from vegetation and covered with plastic sheets. If possible, adopt just-in-time delivery practices, so that
wood does not sit unused and closed in for a long period of time.
Lumber Mold Remediation
There are a number of products on the market, from commercial moldicides to common bleach, which are promoted for
removing mold from wood. However, the U.S. Environmental Protection Agency suggests using mild detergent and water for
most mold clean up. For cleaning wood surfaces, the EPA recommends wet vacuuming the area, wiping or scrubbing the mold
with detergent and water and, after drying, vacuuming with a high-efficiency particulate air (HEPA) vacuum.
If commercial chemical products are used for cleaning mold, be sure to follow the manufacturer's instructions. These products
prevent the growth of mold, sap stain and other fungi. These products can be used on any new building materials before or after
installation for protection against fungal growth. The product can also be used in existing buildings wherever mold growth is a
problem.
Common bleach also can be used, particularly to clean the discoloration cause by fungi. The U.S. Centers for Disease Control
(CDC) recommends using a solution of 10 parts water to 1 part chlorine bleach to clean mold from surfaces. When using bleach
and other cleaning chemicals indoors, make sure there is adequate ventilation and wear personal protection equipment. Never
mix bleach with ammonia.
There are some recommendations about mold remediation on lumber:
If you walk into a retail lumber store or a lumber yard, you will notice a variety of scattered discoloration on almost every piece
of lumber. Lumber mold is found on many construction materials as a result of being exposed to high humidity for extended
periods of time during construction too.
Lumber is an excellent source of nutrition for fungal growth. Wood is primarily composed of cellulose and lignin. It also contains
sugars, starches, proteins, lipids, and fatty acids. Even after a tree is harvested, all of these materials remain in the wood and
provide a food source for fungi. Prior to harvesting, the bark of the tree serves as a protective skin. It is when the bark is
removed that the tree is susceptible to mold growth.
Fungi can grow naturally on lumber under certain conditions. Moisture content above 20 percent for a week is required for
fungal growth on lumber and wood structures.
This review article is about the molds that can grow in lumber yards and at building construction sites. Based on the ability to
penetrate the lumber wood tissue, these fungi are grouped into two main groups, (i) sap stain fungi and (ii) surface fungi.
Sap Stain Fungi
Sap stain fungi affects the sapwood of lumber. Sap stain fungi utilizes sugars, starches, proteins and fats stored in the sap wood
tissue as nutrients. Sap stain fungi cause discoloration of wood tissue by their darkly pigmented mycelia, spores, and melanin
produced by the fungi. Sap stains appear as gray, black or bluish discolorations of the sapwood.
A very common example of sap stain fungi is the Ceratocystis/Ophistoma group which appears on framing lumber and which is
more commonly knows as "blue stain". This is found on lumber as it arrives from the lumber yard, a condition that is readily
apparent to a building expert and which can be confirmed by sample identification.
The most prevalent fungi in stored logs and lumber are those which affect mainly the sapwood, and the resulting damage is
called "sap stain". It causes objectionable discoloration and darkening of the wood. In most cases, the strength of the wood is not
affected. However, where heavy sap stain is prevalent, the toughness of the wood or its ability to withstand shock may be
reduced. The difference between sap stain fungi and surface fungi is the depth of discoloration. Typical sap stain penetrates
deeply into the sapwood and cannot be removed by surfacing or chemical cleaners. The damage to the wood from lumber mold
is cosmetic only, not structural.
Surface Fungi
Molds do not discolor wood as deeply as sap stain fungi. In most situations, surface mold growth is a superficial phenomenon
that does not affect the strength or long-term durability of the wood. Mold gives a fuzzy and powdery appearance of various
colors including gray, black, brown, green and white.
Most of these fungi, however, are commonly found as airborne fungal spores in our environment that subsequently set on
surfaces of wood. When the environmental conditions are suitable, spores will grow and cause wood discoloration.
Some fungal species, including species of Acremonium, Alternaria, Aspergillus, Cladosporium, Paecilomyces, Penicillium, Mucor, Phoma,
and Trichoderma, can grow on the surface of freshly cut wood. These fungi utilize the carbohydrates (e.g., sugar, starch) in the
wood as a source of nutrients. The surface mold causes discoloration of the wood surface by their pigmented spores and/or
mycelia, but they generally do not damage the wood structure.
The way to distinguish between sap stain and surface fungi is to lightly rub the surface of the wood that shows discoloration.
Surface fungi can be brushed off or smeared and removed, whereas sap stain fungi is not removable due to their deep
penetration in the wood.
Fungal Growth Requirements
Four conditions are required for fungal growth to occur on lumber:
1. Moisture (over 20%)
2. Favorable temperature (Approx. 50-90 degrees Fahrenheit)
3. Oxygen
4. A source of food (wood fibers)
If any of these four conditions is removed, fungal growth or infestation will not occur. Mold requires moisture to survive, so
protecting lumber and wood structures from moisture will prevent mold growth.
Health Effects
There is no scientific evidence that lumber mold poses a health hazard. However, mold may be allergenic, as is typical of fungi in
general. If so, the persons at greatest risk are lumber yard workers or carpenters, but no reference is made in the literature to
these occupations being at risk. In addition, no risk has been documented for occupants of homes built with wood containing
Ceratocystis/Ophistoma. Individuals who have mold allergies or suppressed immune systems (such as may be the case for those
receiving treatment for cancer or HIV), have a greater likelihood of reacting to the presence of mold. However, once lumber
mold is encased within a wall system, there is little chance of exposure and as such, ill health is unlikely. Clearly, mold from
outdoors entering a home through opened windows or doors is a far greater source of indoor mold.
Framing lumber in a newly finished house is typically encased by panels or siding on the outside and drywall or panels on the
inside. As such, there is virtually no chance for occupants in a home to be exposed to any mold on the wood through skin contact
or ingestion.
Inhalation exposure to mold on framing lumber in a finished home is possible,but not very likely. Mycotoxins are not volatile, so
they cannot "off-gas" into the environment or migrate through walls or floors independent of a particle. Since particles cannot
move through solid objects, mycotoxins in molds contained inside a wall or floor cavity will stay there unless disturbed.
A California family recently negotiated a landmark 22.6 million dollar settlement in a toxic mold case, claiming that moldy lumber
used to build their house created a "poison prison" that severely injured their son.
Mold Contamination of Newly Built and Under Construction Houses
Newly built and under construction houses could be mold contaminated even before the new homeowner moves in. There are
the following possibilities for mold contamination:
- Moldy building materials including lumber are received from the builder's supplier.
- The builders fail to inspect for mold to prevent moldy building materials from being used.
- The builders store the inventory of building materials directly on the outside ground which allows water to spread from
the ground into the building materials. Also, they do not protect the building materials from rain, by covering with plastic
sheeting, which supplies the necessary water to enable mold to grow in and on the materials. - The construction crew fails to cover the entire home under construction with plastic sheeting at the end of each
construction day. The roof and side walls need to be protected against rain until the entire roof shingles, siding, windows
and doors are totally installed to seal out rain/ - The builders fail to inspect and test the home for mold growth while it is being constructed and also at the completion.
Prevention of Mold During New Home Construction
- Construct a mold-free home. The builder should check the condition of the lumber immediately upon delivery to the site.
- Inspect the lumber and building materials used, and reject moldy lumber and building materials from being used in the
construction of the home. - Keep the job site inventories of building materials off the ground and covered with plastic sheeting.
- At the end of every working day, cover the entire home with plastic sheeting to protect it against rain until the roof is
completely shingled, the exterior siding is completed, and the windows are installed and closed. - Do mold inspections and testing during the construction process so that you can monitor whether or not the home is
being built mold free. - Remove any mold contaminated lumber or building materials discovered during your mold inspections and testing.
As a summary, the key for preventing moldy lumber is to purchase dry wood and keep it dry. Store wood properly by keeping
it off the ground, away from vegetation and covered with plastic sheets. If possible, adopt just-in-time delivery practices, so that
wood does not sit unused and closed in for a long period of time.
Lumber Mold Remediation
There are a number of products on the market, from commercial moldicides to common bleach, which are promoted for
removing mold from wood. However, the U.S. Environmental Protection Agency suggests using mild detergent and water for
most mold clean up. For cleaning wood surfaces, the EPA recommends wet vacuuming the area, wiping or scrubbing the mold
with detergent and water and, after drying, vacuuming with a high-efficiency particulate air (HEPA) vacuum.
If commercial chemical products are used for cleaning mold, be sure to follow the manufacturer's instructions. These products
prevent the growth of mold, sap stain and other fungi. These products can be used on any new building materials before or after
installation for protection against fungal growth. The product can also be used in existing buildings wherever mold growth is a
problem.
Common bleach also can be used, particularly to clean the discoloration cause by fungi. The U.S. Centers for Disease Control
(CDC) recommends using a solution of 10 parts water to 1 part chlorine bleach to clean mold from surfaces. When using bleach
and other cleaning chemicals indoors, make sure there is adequate ventilation and wear personal protection equipment. Never
mix bleach with ammonia.
There are some recommendations about mold remediation on lumber:
- The first step in mold remediation is to remove the source of the excessive moisture so mold growth ceases. Identify and
correct any underlying moisture infiltration or exposure problems. - The most common recommendation is to clean the wood with a solution of bleach and/or soap and water.
- Use a brush or sponge to scrub the surface with a commercial cleaner formulated for mold removal or use a diluted
solution of bleach. - Rinse and allow to dry before covering, enclosing or painting.
- Wear gloves when using chemicals. The cleaned area should be properly dried. Dispose of any sponges or rags used to
cleaned the moldy areas. - Remove and replace damaged building materials that cannot be cleaned.
Sources:
Colonization of freshly pine sapwood surfaces by staining fungi. Dowding, P. 170
Airborne fungal spores at lumber seasoning yards. Unligil et.al., 1974
Fungi causing sap stain in wood. Kaarik, A., 1980
Surface discoloration and blue staining by fungi. Land et.al., 1985
Sap stain of commercial lumber by Ophistoma and Ceratocystis pp. Seifert, K.A., 1993
Seasonal variation of blue stain fungi on pine log and lumber. Uzunovic, et.al., 2000
Lumber Mold - A Concern or Not? Cohen Group, 2002
Mold Remediation in Schools and Commercial Buildings. EPA-USA, 2001
Mold in Construction Checklist. The Centers for Disease Control (CDC), 2002
Mold, moisture and lumber. The Southern Pine Council, 2003
Mold and Wood Products. Western Wood Products Association Publications, 2004
Mold, Housing and Wood. Western Wood Products Association Publications, 2006
Colonization of freshly pine sapwood surfaces by staining fungi. Dowding, P. 170
Airborne fungal spores at lumber seasoning yards. Unligil et.al., 1974
Fungi causing sap stain in wood. Kaarik, A., 1980
Surface discoloration and blue staining by fungi. Land et.al., 1985
Sap stain of commercial lumber by Ophistoma and Ceratocystis pp. Seifert, K.A., 1993
Seasonal variation of blue stain fungi on pine log and lumber. Uzunovic, et.al., 2000
Lumber Mold - A Concern or Not? Cohen Group, 2002
Mold Remediation in Schools and Commercial Buildings. EPA-USA, 2001
Mold in Construction Checklist. The Centers for Disease Control (CDC), 2002
Mold, moisture and lumber. The Southern Pine Council, 2003
Mold and Wood Products. Western Wood Products Association Publications, 2004
Mold, Housing and Wood. Western Wood Products Association Publications, 2006
The information in this article is provided for informational purposes only and should not be used for any other
purpose. Qualtest, Inc. disclaims any liability for any and all direct, indirect, punitive, incidental, special or
consequential damages arising out of the use or interpretation of the information contained in, or any actions taken
or omitted in reliance upon, this article.
purpose. Qualtest, Inc. disclaims any liability for any and all direct, indirect, punitive, incidental, special or
consequential damages arising out of the use or interpretation of the information contained in, or any actions taken
or omitted in reliance upon, this article.