Currently, in North America, there is not an approved test standard to effectively evaluate thermally modified wood to demonstrate it is fit for purpose or longevity from either the International Code Council (ICC), Wood and Door Manufacturers Association (WDMA), or the American Wood Protection Association (AWPA). According to a 2006 blog post on FPInnovations, the Québec Forest Industry Council (QFIQ), FPInnovations, and Cecobois are collaborating with eastern Canadian manufacturers to set up a thermally modified wood classification standard based on four major categories to address fungal degradation, dimensional stability, and colour grade. At this time, nothing has been formalized. Further, no specific code approvals have been provided by the Canadian Wood Council (CWC). In this author’s experience, the significant amount of variables in manufacturing thermally modified wood make it difficult to create code and standard approvals.
In simple terms, wood preservatives, or biocides, such as copper, ammonia, arsenic, and organic pesticides are forced into the wood using a pressure treatment. The wood is first dried—by stacking outside or by kiln drying, steam conditioning, boultonizing, and in some cases incising—so it is receptive to the preservative.
According to Wood Preservation Canada (WPC), preservatives work by penetrating the wood, neutralizing the food supply within the material, and providing protection outlasting the product’s useful life. These treatments have a lifespan of 10 to 20 years. Just like other treatments, this product’s lifespan depends on variables such as climate, finishing (coatings), maintenance, and proper installation. Pressure-treated wood is also one of the more affordable preserved wood products on the market, and the most widely used.
One of the most talked about and debated preservatives in North America is chromated copper arsenate (CCA). It contains inorganic arsenic, chromium, and copper. Inorganic pentavalent arsenate, one of the primary active ingredients in CCA, is a naturally occurring element people come into contact with every day through food, water, air, and soil. Since the 1940s, wood has been treated with CCA for use on outdoor residential structures, such as decks, fences, and children’s play equipment, to protect against fungi, termites, and other insects.
The United States (2003) and Canada (2004) voluntarily phased out CCA’s use in residential areas due to arsenic exposure. Today, it is used for certain commercial, industrial, and agricultural applications with some residential exceptions (wood shakes, shingles, and permanent wood foundations) and is registered for use in Canada under Health Canada’s Pest Management Regulatory Agency (PMRA).
“The most commonly used preservation treatments in Canada today for residential and commercial applications are alkaline copper quarternary (ACQ), copper azole (CA), and micronized copper azole (MCA),” said Martin Tauvette, executive director at WPC, a group representing manufacturers and suppliers of pressure-treated wood throughout Canada.
Choosing the proper preservative-treated wood depends on the intended use. All preservatives are registered and regulated by PMRA. The following are the most common pressure-treated wood products used throughout Canada.
Alkaline copper quarternary
A water-based wood preservative, ACQ’s main ingredient is copper oxide and a quaternary or ‘quats’ ammonia compound. Developed in the 1990s as an alternative to CCA, ACQ adds protection from fungi and insect attack as well as decay. It is used for exterior residential applications such as decks, patios, landscaping, gazebos, fencing, decking, and other wood structures. ACQ types—B, C, and D—offer different ammonia properties or quat compounds depending on the wood species being preserved.
The active ingredients in copper azole are copper and an organic biocide such as tebuconazole. Widely used on field crops, tebuconazole offers fungicidal protection and works as an active co-biocide with copper. CA is used on exterior residential applications like decks, patios, landscaping, fencing, walkways, and boardwalks.
Micronized copper azole
The most recently developed wood preservative, MCA uses micronized copper (nanoparticles and micron-sized particles of copper carbonate) and micronized tebuconazole together to use on exterior residential applications above- or in-ground and in freshwater contact.