A ToolBase TechNote
Pressure treated wood is used extensively for residential purposes including decks, playground equipment, outdoor furniture, foundations, retaining walls, trellises, and a host of other uses. It is also used for industrial applications such as utility poles, railroad ties, bridge members, and other structural uses exposed to potential decay.
Chemicals used to pressure impregnate lumber are numerous, but the most commonly used wood preservative for residential products is chromated copper arsenate or CCA, which comprises over 90 percent of the market. Southern pine is the predominant species that is treated with CCA.
There have been concerns expressed about the safety of CCA-treated lumber. Arsenic is the chemical that generates the most concern among the general population. CCA lumber has been studied extensively regarding its propensity to impact environmental or human health. At this time, there is no consensus regarding the health risk of CCA-treated wood products.
Recently, several organizations in Florida have banned the use of CCA-treated wood and, in some cases, have had treated structures removed. The Environmental Working Group and the Healthy Building Network in 2001 lobbied the Consumer Products Safety Commission to ban the use of CCA-treated wood in playground equipment and the EPA began to study treated wood safety in playground applications that same year.
Concurrently, CCA, as an EPA-registered pesticide, is being evaluated as mandated by the Federal Insecticide, Fungicide, and Rodenticide Act, which directs the EPA to periodically re-evaluate all registered pesticides to ensure conformity of current safety standards prior to re-registration.
In February 2002 the EPA announced a voluntary decision by the three manufacturers of CCA to phase out the production of arsenic-containing treated wood for residential use by year end of 2003. The EPA will not permit the production of CCA products intended for residential use after this date.
Alternatives to CCA
Several products are available as an alternative to CCA-treated wood.
Alternative Preservatives
Ammoniacal Copper Quat (ACQ-Types A, B and C) - Wood treated using this preservative is marketed under the brand name ACQ Preserve by Chemical Specialties, Inc. or CSI.
Amine Copper Quat (ACQ-D) - Similar active ingredients to ACQ-A but uses ethanolamine instead of ammonia to act as the treating solution carrier. Lumber treated with this preservative is marketed as NatureWood by Osmose.
Collectively, all of the ACQ products are sometimes referred to as alkaline copper quat preservatives.
Copper Azole-Type A (CBA-A) - Another new generation wood preservative that contains copper and boron. Wolmanized Natural Select by Arch Wood Protection (formerly Hickson).
Borate Oxide (SBX) - A class of wood preservatives that contain boron as the active ingredient. Borate compounds include sodium octaborate, sodium tetraborate, sodium pentaborate, and boric acid. Borate oxide preservatives are water soluble and do leach. Therefore, they are not recommended for wood in soil or constant water contact. Brand name products containing borate compounds include AdvanceGuard lumber by Osmose and SmartGuard products from Louisiana Pacific Corporation.
Non-preservative options for treated wood include naturally durable wood species and non-wood products such as plastic lumber.
Naturally Durable Wood
Naturally durable species such as redwood, cedar, locust, and others derive their durability from chemicals deposited in the tree during their life cycle. As a tree ages, these chemicals become more concentrated. It is key to note that these chemicals are only present in the heartwood (center) of the tree or log and that old growth trees are more resistant to decay than younger trees. Sapwood (wood toward the bark) of even decay-resistant species is highly susceptible to decay. In addition, these chemicals, collectively called extractives, are water soluble and so they (and the decay resistance) leach out over time.
Non-Wood Options
Non-wood products such as plastic lumber are highly resistant to decay, but may not be decay proof. Boardwalks constructed of wood-plastic lumber in Florida have been found to support fungus. In addition to decay resistance, structural properties of alternative materials are important. Most makes of plastic lumber are not structural in nature and so their application is limited.
Cost of Alternative Wood Treatments
Currently, the cost of treated wood with alternative pesticides is estimated to cost about 10 to 20 percent more than CCA-treated wood. In addition, availability of alternatively treated wood is greatly limited compared to CCA material. Over time, however, the availability of these products will greatly improve as CCA is phased out.
Should I Remove or Treat my Existing Deck?
The EPA is not advocating this strategy and no scientific study suggests these actions are warranted.
For those wanting to reduce the chance of preservative leaching, the application of a semi-transparent penetrating stain or a water-repellent finish has shown some promise in preventing the leaching of copper, chromium, and arsenic from treated wood.1 2 It should be noted, however, that surface treatments need annual re-application to maintain water repellency.
Film-forming finishes such as solid or heavy-bodied stains or paints have not shown evidence in the prevention of preservative leaching. On wear surfaces or high-traffic areas, the potential for paint film cracking and blistering is high. In addition, varnishes and paint films may make surfaces highly slippery subjecting people to injury from falls. Clear films such as varnishes are not durable in ultraviolet light and fail early requiring frequent refinishing.
Identification of Treated Wood
The identification of the specific preservative used to treat wood is extremely difficult for the layperson. The presence of a green color does not necessarily mean CCA or other arsenical was used. The green color suggests the presence of copper, which many other preservatives contain. In addition, some manufacturers have produced non-green, CCA-treated products to appeal to buyers disliking the green color. Over time, all wood (treated or otherwise) will weather to a gray color due to sun and water effects. Therefore, color is not a good identification tool.
If the wood is treated, it was probably treated with CCA because it comprises the vast majority of the residential treated wood market. Often, lumber is marked with a stamp that indicates the standard under which the lumber was treated as well as the preservative used. These stamps, however, are not always present, or can fade or become obscured over time.
1 Lebow, S. T. and M. Tippie. 2001. Guide for minimizing the effect of preservative-treated wood on sensitive environments. Gen. Tech. Rep. FPL-GTR-122. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 18p.
2 Cooper, P.A. and Y.T. Ung. 1997. Effect of water repellents on leaching of CCA from treated fence and deck units-An update. IRG/WP 97-50086. Stockholm, Sweden: International Research Group.