Treated Pine Lumber for Decks: Types and Benefits of Treatments1 January 2013
If building a deck, be sure to learn about recent advances in wood-treatment technology. Treatments help extend your deck lumber’s life and protect it from insects, fungi and moisture. Alkaline copper quaternary (ACQ) and copper azole (CA) treatments remain available, while newer methods employing micronized copper (MCQ and MCA) offer significant benefits.
Decks have grown in popularity as people have realized the benefits of a raised outdoor platform for summer barbecues and other leisure activities. Evolving with that trend has been the science of making safer, more effective and protective wood treatments.
Some people build their decks of untreated cedar and redwood because of their natural rot resistance, or of artificial materials. However, for durability, economic and other reasons, most deck builders prefer yellow pine. Many organisms also like yellow pine, so it must be treated to extend its product life and protect it from insects, fungi and moisture.
Types of treatments
Decking lumber is most often pressure-treated with water-borne preservatives. During treatment, pressure is applied to force the chemical preservative into the wood in an enclosed cylinder.
For decades, the water-borne preservative most commonly used to treat wood for decks was chromated copper arsenate (CCA). By 2004, the U.S. Environmental Protection Agency began restricting CCA-treated wood in residential applications, such as decking, because of safety concerns related to the preservative containing arsenic and the heavy metal chromium.
In the years since then, wood treatment for residential applications have primarily been by a couple of non-arsenic, copper-based preservatives:
Alkaline copper quaternary (ACQ), compared with CCA, is more corrosive to hardware and fasteners and is more likely to leach copper. It is sold under different brand names, including Preserve and NatureWood. The treatment initially wears to a natural brown color and eventually turns gray following long-term exposure to the sun, if left uncoated or with clear water repellent coatings, according to Viance, the makers of Preserve. For use with ACQ-treated wood, they recommend hot-dipped galvanized or stainless steel fasteners and fittings, and not aluminum fasteners and fittings.
Copper azole (CA), too, is more corrosive than CCA. However, wood treated with copper azole is sometimes said to have a greenish hue similar to that with CCA-treated wood products. In the U.S., CA-treated wood is marketed under the Wolmanized brand by Arch Wood Protection.
More recently, innovative products with new advantages have become available:
Micronized copper quaternary (MCQ)and micronized copper azole (MCA) employ fine particles of copper as their preservative. Micronized copper treatments cause little to no corrosion and do not change the natural wood color. They also do not pose the safety concerns CCA does. Another advantage of MCQ- and MCA-treated products is they are approved for contact with aluminum trims, fasteners and other building products in code-compliant, above-ground applications such as decks. Micronized-copper-treated products are made by different manufacturers. The best known one is Osmose, which uses its MicroPro process to treat its YellaWood products.
Some other new wood-treatment products have entered the market but are lesser known and not as widely available.
As of April 2009, the MicroPro copper-treatment system is the only wood preservative process that has received the Environmentally Preferable Product certification from Scientific Certification Systems. Products with this designation are deemed to impact the environment less than other products that serve the same purpose. MicroPro’s EPP designation was based on an environmental review process in accordance with the International Organization for Standardization. Compared with standard wood-treatment processes, the environmental benefits of MicroPro reported by Osmose are significant:
- Total energy consumption is reduced by about 80 percent.
- Air and greenhouse gas emissions are greatly reduced.
- The release of copper by treated products into aquatic and terrestrial environments is almost eliminated.
ACQ, CA and MCQ treatments are all currently available and comparable in price, but they have not all been evaluated by the same regulatory organizations. ACQ and CA treatments have been evaluated by the American Wood Protection Association and are listed in their standards. The MCQ system, which is newer, has not yet been submitted to the AWPA for evaluation. Though AWPA is considered the primary standard-setting body for pressure-treated wood, Osmose instead submitted its patent-pending product to the International Code Council Evaluation Service Inc., which has tested and approved the Osmose MCQ treatment for building code requirements.
Because of that decision by Osmose, one of its competitors has launched a negative campaign, which has caused confusion and stirred controversy in the industry. Osmose officials said their decision to go with the ICC over the AWPA was for proprietary reasons and noted that major building codes in the United States recognize AWPA and ICC-ES equally for product performance, evaluation and certification marks.