When most people think of treated wood the first thing to come to mind is outdoor decks. Structures built outdoors are exposed to many damaging environmental conditions including rain, snow, insects and ultraviolet radiation. Wood treatment with preservatives is recommended to extend the life of any exterior wood. Approximately 40% of treated lumber in North America is used in the construction of decks. Although everyone has walked on a treated deck, most know little history of the treated wood.
In the first half of the 19th century, wood was commonly treated with oil borne preservative systems such as those used to treat railway ties. A high level of protection was achieved however the finished product was aesthetically unsuitable for residential decking applications. At the time majority of the decks built were from naturally durable species such as cedar and redwood.
The early 1970's a copper based preservative know as chromated copper arsenate was introduced to the decking market. Wood preservative companies were trying to expand applications of their products and captured the residential decking market with great success. Wood treated with chromated copper arsenate gained market share over the next 20 years at the expense of naturally treated wood.
In 2001, consumers became concerned about the risks associated with chromated copper arsenate treated lumber. In particular, the use of arsenate on structures contacted by children was brought discussed. Although scientific studies suggested there were no risks associated with chromated copper arsenate preserved wood, it was voluntarily removed from the residential market on December 31st, 2003. Today chromated copper arsenate is still used as a preservative for agricultural applications, wood foundations, treated plywood and other industrial uses.
Ammonium copper quaternary and copper azole were introduced as alternatives to chromated copper arsenate lumber. Protection provided was similar to previous generations of chromated copper arsenate, however ammonium copper quaternary and copper azole were more corrosive requiring the need for heavily coated fasteners. All three systems chromated copper arsenate, ammonium copper quaternary and copper azole contain copper to that protects the wood. Additionally, copper is what gives treated wood a greenish appearance.
Micronized copper systems were introduced to the treated wood market in 2008. Small microscopic pieces of copper are deposited into the wood cells during the treatment process. The result is lumber with similar durability as previous generations of preservative systems, however corrosion of fasteners is minimal. In the United States today, micronized copper preserved wood is used for a majority of the decks. In Canada, treated wood is still treated with ammonium copper quaternary and copper azole however a shift to micronized copper preservatives is expected to occur in the near future.
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