Adhering to a New Standard of Excellence in Innovative Building Materials

CLT Construction – By Darryl Byle,

It’s a sticky problem that Forest Products Laboratory (FPL) researcher Juliet Tang in collaboration with faculty member Hyungsuk Lim and graduate students from the Department of Sustainable Bioproducts, Mississippi State University, find themselves researching.

Juliet Tang
Research Forest Products Technologist
Durability and Wood Protection Research

The team is brainstorming innovative ways to make the building material of the future—mass timber—more versatile. But in order to do that, they have to find an adhesive and a preservative, two substances that tend to be uncooperative together when used on timber, that will work concurrently for optimal bond strength and durability.

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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.