Coastal builders and remodelers rely on preservative-treated wood for a range of uses, including decks, boardwalks, landscaping, and accessory structures. So when wood treaters made an agreement with the Environmental Protection Agency in 2003 to change their wood-treating formulas, coastal contractors were directly affected.
The old CCA formula, based on chromium, copper, and arsenic, was pulled off the market as of 2004. In its place came ACQ (Ammonium Copper Quaternary) and CA (Copper Azole). Chemical suppliers kept the copper, which is considered relatively safe, but added a few new "co-biocides." Alongside the copper, ACQ uses quaternary (or "quat"), a compound based on ammonia with some added elements, including chlorine. Copper azole uses tebuconazole and propiconazole, two EPA-registered pesticides already well-established in agriculture for control of fungi and insects (grape growers in California are the biggest users of tebuconazole).
Early copper-based formulations used to replace CCA in pressure-treated wood came with their own set of problems related to the corrosion of metal connectors and fasteners. Despite claims that new "micronized" copper formulas have solved that problem, many coastal contractors still prefer stainless steel fasteners.
But ACQ and CA created a new problem: metal corrosion. They're not compatible at all with aluminum flashing or aluminum nails, and they also may attack galvanized nails and screws, galvanized flashing, or galvanized connectors and joist hangers. The corrosion issue prompted Simpson Strong-Tie to come out with new, more heavily galvanized hardware, and to recommend exclusive use of stainless steel hangers for coastal areas. Simpson posts information and recommendations about the corrosion issue.
But technology is still changing fast in the world of treated wood, most notably in the way copper is applied to the wood. ACQ and CA use copper dissolved in an ammonia or amine carrier. By 2007, new "micronized" formulas, which use finely-ground solid copper particles in a mostly water-based carrier, were pushing ACQ and Copper Azole out of the picture. Already, "micronized copper quat," "micronized copper azole,", and "dispersed copper azole" account for about 80% of the market for residential treated wood, according to industry expert Mike Freeman (www.wooddoc.org). Common brand names for the micronized systems include "Micro Pro" from Osmose, "SUSTAIN" from PhibroWood, and "µCA-C" from Arch Treatment Technologies.
The vendors claim that these new micronized formulas are less aggressive and corrosive toward fasteners, hangers, and flashings. Micro Pro, according to Osmose, is even okay in contact with aluminum flashing. But outside of the vendors themselves, it's hard to find third-party confirmation for these assurances. Simpson Strong-Tie's experts, for example, recommend the same level of galvanizing for connectors used in contact with the new micronized formulas as they recommended for ACQ. Of course, use conditions make a difference, and coastal environments carry a higher risk of corrosion because of salt spray and salt vapor in the air. Within a few miles of the coast, or even near a swimming pool where chlorine is a factor, Simpson still calls for stainless steel — no exception for micronized treatments.
If you want to keep up with the changes, you have to study. One excellent general resource for contractors is this free PDF download from the Southern Pine Council, " Pressure-Treated Southern Pine."
Even better for coastal builders (and also free) is " Treated Wood in Aquatic Environments," a long, detailed handbook about dock and pier construction for marine environments, where CCA lumber, ACZA (ammonium copper zinc arsenate) wood, or even creosote and penta formulations may still be permitted because of the tougher conditions.
The changes keep coming. Next year, insiders say, some existing brands that are currently only permitted for above-ground use will get approval for ground-contact applications — including, says Mike Freeman, one formula that uses no copper at all. And the industry is still busy developing new chemical formulas: Richard Vlosky, director of the Louisiana Forest Products Development Center at LSU, says researchers at the school are currently testing and evaluating several innovative preservative systems for industry clients. The Journal of Light Construction (www.jlconline.com) will be taking a closer look at all these developments in spring of 2009. (Hanley Wood, which publishes this newsletter, also publishes JLC.)
Meantime, the International Code Council has been working on new or revised standardized test methods for preservative treatment performance (Acceptance Criteria AC-326), and for assessing fastener corrosion in treated wood (Acceptance Criteria AC-257). Strictly speaking, the 2006 International Building Code (IBC) and International Residential Code (IRC) currently only allow four fastener materials with treated lumber: stainless steel, hot-dipped galvanized steel, copper, or silicon bronze. But hundreds of alternative fasteners are on the market, using various other metals and polymer, ceramic, or metallic coatings, and advertised as suitable for use with ACQ treated wood. None of those alternative screws or nails have building code recognition yet — because the new criteria for acceptance, AC-257, has only just taken effect as of January 1, 2009. However, by year's end many coated screws are likely to have gone through AC-257 testing, and received formal Evaluation Reports from the International Code Council Evaluation Service (ICC-S).
We'll keep you posted as the situation develops.