Reconsidering Rot-Resistant Framing Material
Copper- and borate-based preservative treatments have proven effectiveness, but structural plastics are more durable.
Synopsis: When copper chromated arsenate (CCA) was eased off the market at the end of 2003 due to fears about its toxicity, builders needed to find new sources for rot-resistant structural lumber. As contributing editor Scott Gibson has discovered, the industry has responded by developing three new types of rot-resistant framing materials. The new materials include lumber treated with alkaline copper quaternary (ACQ) or copper azole (CA); wood treated with borate, a naturally occurring mineral salt; or fiberglass-reinforced plastic lumber (FRPL), made from recycled plastics. The article includes a sidebar about new compounds and organic treatments in development.
For 60 years or so, a compound called chromated copper arsenate (CCA) successfully protected structural lumber from the harmful effects of weather, bugs, and microbes. Eased off the consumer market at the end of 2003 due to concerns about its toxicity, CCA was replaced by two other compounds also rich in copper but without the arsenic or the chromium: alkaline copper quaternary (ACQ) and copper azole (CA). Now, nearly four years later, they remain the only residential choice for treated wood rated for ground contact.
Technology in lumber treatment is moving forward, however. Manufacturers are working hard on more benign organic compounds that not only eliminate the corrosive effects of traditionally treated lumber products but that also can be used directly in the ground.
Until that technology is ready for market, three effective structural materials can be used when mold, insects, and decay are a concern. Each has varied applications, levels of protection, and price differences.
Copper-based ACQ and CA are highly recognizable materials that continue to dominate the preserved-wood industry. Borate-infused lumber is not a new technology, but it is a fast-growing, nontoxic alternative to metal-based treatments. And plastics, which typically have been thought of only as decking material, are emerging as another viable…