Next year, lumber that has been pressure treated with CCA (chromated copper arsenate) will be phased out of residential use. But will replacement materials have the same properties as their predecessor? A recent news bulletin from the NAHB notes that several of the common alternatives to CCA--including ACQ (ammoniacal copper quat), CA (copper azole) and CBA (copper boron azole) create higher corrosion rates in metals than does CCA.
Cliff Jones, marketing director for Osmose, the company that produces NatureWood, an ACQ-treated lumber, allows that some alternatives to CCA do interact more aggressively with metal fasteners, but he describes the corrosion (compared with CCA) as "marginal."
Jones also insists that borate-treated wood such as AdvanceGuard (also made by Osmose) should not be lumped together with ACQ- and CA-treated lumber because it is not intended for exterior applications, he explains. "There's no issue of corrosion there," he says.
Jones defers to the advice of fastener manufacturers for best practices with the new treated materials. "We generally recommend hot-dipped galvanized or stainless fasteners--but we're not metal experts."
Some manufacturers have recommended that builders use screws and nails with a heavier-than-typical galvanized coating, such as G185, when working with ACQ lumber.
A bigger long-term threat to wood's dominance might be the rising market share of wood-plastic composites. Read next month's (January 2004) issue for more on how plastic wood has capitalized on the treated lumber changeover.