There’s a Superhero Beneath Your Feet

Imagine a trail dipping below a steep valley edge surrounded by lush, verdant greens. A brook chatters below and in its soft watery tones invites hikers to a moment of relaxation and communion. The breeze is soft and sweet as the leaf canopy dances in unison overhead. It is idyllic and accessible because of the wooden boardwalk solidly supporting each who visit this natural wonder.

This boardwalk and others like it can be found in many natural areas. But it is made possible by pressure-treated wood, a building material that when processed with the correct preservatives, often outlasts and outperforms durability estimates and usefulness before it can biologically deteriorate.

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Time in a Bottle: Finding New Life for an Old (Yet Reliable) Test Method

The simple soil bottle presents an extremely useful tool for predicting performance of preservative treated, modified or naturally durable woods. The methodology was developed in the 1940s exclusively for evaluating wood preservatives against wood decay fungi. It has been adapted over several decades to include naturally durable woods, wood plastic composites, and engineered wood products, and we use it constantly here at the Forest Products Laboratory (FPL).

The basic premise of the soil bottle is a material is presented to an actively growing fungus in an otherwise sterile environment. The resistance of the material to fungal degradation is determined by comparison to reference materials (non-durable species or treated reference material). The soil bottle also presents an excellent tool for studying basic fungal biology whereby cellular changes in wood during the decomposition process can be analyzed.  The soil presents a refuge for the decay fungus as well as a source for moisture and transported ions relevant to the decay process.

Past, present and future research at FPL is looking at ways of modifying the standard soil bottle setup to be even more useful for the evaluation of wood and wood protectants. Here are just a few examples of where FPL researchers are pushing the boundaries of the standard soil bottle: Continue reading

Essential Science: Researchers Patent a New and Natural Frugal Fungicide


A selection of different composite wood products both untreated and treated with essential oil. The samples dipped in essential oil exhibit far less mold growth.

Sitting at the Forest Products Laboratory (FPL), microbiologist Vina Yang recounts a news story that took Madison, Wisconsin by storm. Fourteen years ago, more than 35 students and faculty mysteriously fell ill at Caesar Chavez Elementary School. Although the school had only been open for two months, it quickly and inexplicably turned from Madison’s newest educational institution into a health nightmare. Ailments ranged from sudden onset asthma, to respiratory problems, to severe allergic reactions, and it was only after the school’s inevitable closure that officials found the source of the problem—hidden behind the pristine drywall and gleaming floor tiles of the new building, inadequate ventilation had caused mold to take a firm hold at Caesar Chavez.

Today, Yang and fellow researcher Carol Clausen are working hard on developing new techniques to combat the mold plaguing the world’s wood-containing residences, businesses, and storage facilities. More than seven years of research recently culminated in a patented method of using essential oils derived from plants to inhibit mold on cellulose-containing materials such as paper, lumber, and ceiling tiles.

Yang and Clausen’s Durability and Wood Protection unit traditionally studies preservatives for wood in exterior applications, but it quickly became apparent that there was demand for a less toxic solution for indoor use as well.

“We would always take calls from consumers asking for ways to prevent mold on the inside of houses,” Clausen recalls, adding that essential oils can be as effective as chemical fungicides without the associated health concerns, which are elevated when used in a household environment. Perhaps the biggest, albeit subjective, drawback of using the oils indoors is the odor, as they tend to smell strongly of the parent plant. “One person came by the lab and just loved the smell—others came by and told me to close the door,” added Yang.

From the original arsenal of seven oils that Yang and Clausen began to study in 2007—thyme, ajowan, dill weed, Egyptian geranium, lemongrass, rosemary and tea tree—only the thyme oil compositions received the patent earlier this year. Patent Number 8,986,757 now awaits licensees and industry partners to deliver new products to consumers.

Yang suggests that applying the oil to wood stored in warehouses or lumber yards could prolong its storage life, while Clausen foresees the treatment as an easy way for companies to provide peace of mind to consumers. “I especially foresee a lumber or construction company using our technology as a way to provide inexpensive protection to customers,” Clausen said.

The oil can be dipped, sprayed, or brushed onto wood surfaces, and in some cases, simply exposing the material to oil vapor is enough to inhibit mold growth, making it the ideal process for fumigating large spaces or large volumes of material.

A photograph illustrating the effectiveness of essential oil as a mold inhibitor when applied to wood as an oil vapor. The treated wood stakes (left) experienced far less mold growth than their untreated counterparts (right).

A photograph illustrating the effectiveness of essential oil as a mold inhibitor when applied to wood as an oil vapor. The treated wood stakes (left) fared much better than their untreated counterparts (right).

Essential oils cost roughly $18.00 per pound, and when they are diluted for use, the cost is about two cents per gallon, and fractions of a penny per square foot. Essential oil technology becomes even more affordable when one considers that health problems caused by interior mold accounted for $2.8 billion in 2002 alone.

The research may have come a bit late to rescue the doomed Caesar Chavez Elementary School and prevent the legal action that resulted from the building’s poor construction, but both researchers hope that in the future, new buildings will benefit from these surface treatments.

Clausen cautions that although effective, essential oils are not a replacement for public education or good building practices such as the proper installation of ventilation systems or flashing.

“Prevention is the key, and educating the consumer is huge, especially in flood prone areas or in regions that face seasonal problems with mold,” Clausen said. “If they could just keep the buildings dry, that would solve all of their problems.”

Cedar Shake and Shingle Bureau: The Rules and the Secret to the Labels

The Cedar Shake and Shingle Bureau (CSSB) is a nonprofit organization that oversees the inspection of western redcedar (Thuja plicata), Alaska yellow-cedar (Chamaecyparis nootkatensis), and redwood (Sequoia sempervirens) shakes and shingles. The CSSB publishes quality standards (grade rules) and ensures that the member mills producing shakes and shingles meet these standards through periodical third-party inspection.

Shakes and shingles with CSSB designations have been inspected to meet grade standards. A grade stamp/label (with color code for the grade) is placed on each bundle or carton of shakes or shingles and clearly shows the grade. The label contains other information such as wood species, certifying agency, building code standards, and manufacturer. This “Certi” label assures the consumer that the shake and shingle manufacturer is adhering to grading rules as prescribed by building codes.


Figure 1. Information on a Certi-Label™: 1) “Certi” brand name; 2) Product grade; 3) Product type; 4) Independent third party quality control agency; 5) Compliance with total quality processes; 6) Manufacturer; 7) Industry product description; 8) Product dimensions; 9) Cedar Shake and Shingle Bureau label number; 10) Building code compliance numbers; 11) Product performance tests passed; 12) Label identification number; 13) UPC code; 14) Coverage showing the number of bundles/100 square-feet and recommended exposure; 15) Application instruction on reverse side. Used with permission from Cedar Shake and Shingle Bureau Exterior and Interior Wall Manual.

Looking into the Future of Wood Preservation

Carol Clausen and her group are serious about wood as a sustainable and versatile building material. Here Amy Blodgett, Rachel Arango, and Bessie Woodword check soil block samples in their ongoing research.


Members of the Durability and Wood Protection Research Unit check soil block samples.

The soil block decay test method determines the minimum amount of preservative that is effective in preventing decay of selected species of wood by selected fungi under optimum laboratory conditions. Conditioned blocks of wood are impregnated with solutions, emulsions, or dispersions of a preservative in water or suitable organic solvent to form one or more series of retentions of the preservative in the blocks. After periods of conditioning or weathering, the impregnated blocks are exposed to recognized destructive species of both brown-rot and white-rot wood-destroying fungi.

Speaking about her work, Clausen says that wood’s “increased use in construction minimizes life-cycle impacts of a structure while maximizing carbon storage for the life of the structure.” An upcoming report by Clausen, Frederick Green III, Grant Kirker, and Stan Lebow summarizes presentations and comments from the inaugural Wood Protection Research Council meeting, where research needs for the wood protection industry were identified and prioritized.

As a part of that conversation, Clausen states that chemicals used to protect wood from deterioration by fungi and insects have generally been broad-spectrum biocides that have been discovered by the traditional screening approach. However, a more logical approach is to develop selective and targeted biocides by defining the target first, characterizing that target, and then designing inhibitors based on the mechanism of action of the defined biotarget.

Despite substantial progress in explaining the biochemistry of wood degradation, biochemical targets for fungal inhibition have seldom been described. Discovering the mechanism of preservative tolerance(s) in economically important fungi and insects will enable researchers to design preservative systems that neutralize, block, prevent, and eliminate the preservative tolerance. Development of a genetic database of microbial activity during the process of wood deterioration will offer a better understanding of precisely how and when decay or insect attack begins. A molecular database would provide myriad of capabilities to the wood preservation community. For example, researchers could characterize decay risks for a particular location, define the prevalence of tolerant fungi on a national and international basis, and determine the influence of preservative exposure on the ecology at test plots.

The next generation of novel wood protection methods may incorporate nanotechnology for design or controlled delivery of biocides for improved durability of building materials, with an emphasis on engineered composites. Nanotechnology may also play a vital role in the development of water-resistant coatings and treatments for the prevention of fire. Results from basic research on genetic analysis, biochemical processes, nanotechnology, and characterization of biotargets will lead to technological developments that extend the service life of wood and wood-based materials in all major end uses emphasizing environmentally friendly methods.