Treated Wood Industry Looks to Toughen Standards

Third-generation wood treater Hal Bumby of Maine Wood Treaters looks at a decades-old treated wood structure on the shore of Sebago Lake in Maine. This deck and staircase, built with CCA (chromated copper arsenate) lumber, is still sound after many years of exposure to weather and ground contact. But newer types of decking and framing lumber would not be warrantied in the same application — not because of a less effective formula, but because of a lower required dose of the treating chemicals. Bumby advocates returning to a policy of ground-contact treatment for all treated lumber: “One product, suitable for all applications.”

Wood treater Hal Bumby walks on a walkway installed on grade using lumber treated with micronized copper azole (MCA) and infused with an integral iron oxide color treatment. The wood is holding up well after several years in place. But the 5/4 boards, like all decking in the market today, are not treated to ground-contact levels and would not be warrantied. Bumby treated the wood at his own Maine facility, and he comments: “I’m a wood treater. And even I am using material that’s not recommended for this application. How can we expect contractors to know the difference?”

A closer look at the colorized deck boards installed as a walkway on grade near Sebago Lake in Maine. This wood contains a copper-based preservative as well as an iron-oxide colorant, both applied deep into the wood using pressure treatment. So far the wood looks fine and is sound, despite the off-label use. But in the event of early decay, the lumber would not be guaranteed because it is not labeled or code-approved for ground contact. In the past, all treated lumber, including deck boards, was typically treated with concentrations of chemical allowing the wood to survive contact with the ground.

This treated wood staircase near a motel in North Dartmouth, Mass., dates back to the 1990s, and was constructed with CCA lumber before the arsenic and chromium formula was phased out. The 2x10 stair stringers are partially buried in the earth. Today, 2x10 lumber treated with MCQ, MCA, or CA preservative formulas would not be approved for this use because the wood contains a lower concentration of the treating formula in order to reduce the treatment cost.

A closeup of the label still attached to the old CCA staircase built on ground in North Dartmouth, Mass., in the 1990s. The number “40” in the label refers to the treatment formula concentration, or “retention” — 40 pounds of retained copper per cubic foot, the level specified for fence posts, landscape ties, and poles in ground or fresh water. This label was taken from a 2x6 board on the walkway, indicating how all treated wood was customarily treated for ground contact in the late 20th century.

A close-up of the label on a piece of CCA-treated wood on a guardrail by a road in North Dartmouth, Mass., near New Bedford south of Boston. The label specifies a chemical loading or “retention” of 40 pcf, suitable for ground contact, although the wood is installed above the ground. The wood has weathered, but is sound and free from rot, despite being subjected to years of damage from road salt, snowplowing, vehicle contact, and weed-whacking.

A view of the end of a fresh 2x6 treated-wood post on a job site in Massachusetts, showing the code-required wood-treatment label. This wood is approved for ground contact, like all treated 4x4 and 6x6 lumber in today’s market. (However, cut ends must be field-treated with a copper naphthenate solution in order to maintain warranty coverage, because the treating chemicals penetrate the wood from the inside out, and chemical concentrations are usually lower near the center of the piece.)

A close-up of the code-required label stapled to the end of a preservative-wood 6x6 Southern Yellow Pine post. The label shows the approved use (“ground contact”), and identifies the treatment chemical (“copper azole”).

Another treated-wood 6x6 post end from the same Massachusetts job site, with a close-up of the required label (inset). The “µCA-C” designation indicates that this wood is also treated with micronized copper and an “azole” pesticide, but using formula supplied by a different chemical company. The label also specifies that the 6x6 is approved for ground contact. As with the other post, every cut must be field-treated using copper naphthenate or the warranty will not be honored. It’s common to see treated lumber from different wood treating facilities, treated with different formulas, on the same job site or on racks at the same lumberyard. It’s up to the end user to make sure that the lumber is appropriate for the application.

The ends of two preservative-treated Southern Yellow Pine 2x10 boards on a Massachusetts job site. The labels on these boards indicate that the wood is not approved for contact with the ground. That’s rarely a problem in a deck framing situation; however, if the boards are used as stair stringers and with the lower ends touching the ground, the use is not approved or guaranteed. Premature rot of treated-wood stair stringers has been reported in that situation — particularly in coastal exposures and in hot humid climates.

A view of a landscaping detail in Maine: a planting box outside a small office building near a road, filled with soil. This application subjects the wood to conditions that are unusually conducive to decay. But the material, 5/4 treated decking, is not treated to levels appropriate for ground contact, and is not warrantied for this application. Building codes do not regulate planting boxes.

Two views of a road-side signpost in rural Maine, sawn from eastern Hemlock wood that has been incised, kiln-dried, and then pressure-treated with dissolved (not micronized) copper azole. Maine wood treater Hal Bumby has been treating signposts like this on a state contract since the 1980s, first using CCA, and then using dissolved copper azole after CCA was phased out. Bumby uses dissolved copper azole instead of finely-ground micronized copper for this purpose because Hemlock is what is called a “refractory” wood species — meaning that it does not readily soak up the treating chemicals. Bumby says that whether treated with CCA or with copper azole, the Hemlock wood is good for decades of service buried in the ground — as long as the proper concentration of the treating formula is applied.

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