MEDIA SPOTLIGHT: New Wood Preservatives Promote Premature Fastener Corrosion

Jason Sandefur

Editor”s Note: Articles in Media Spotlight are excerpts from publications or broadcasts that show the industry what the public is reading or hearing about fasteners and fastener companies.
Recent changes in the composition of pressure-treated lumber are raising concerns about more rapid corrosion in the metal brackets and fasteners used to connect the wood in foundations, decks and other outdoor structures.
According to the Sacramento Bee, government officials warn that builders should match pressure-treated wood with stainless steel or, at a minimum, heavily-coated galvanized fasteners and brackets.
Testing shows the most common new preservatives, which first showed up in pressure-treated lumber in early 2004, are more corrosive to metal than older preservatives with arsenic.
Experts say corrosion rates vary depending on conditions such as humidity. It is unclear how long it would take to achieve failure in various metal fasteners, such as screws and nails, or wood connectors.
“The better the coating you have, the more resistance you have, and the best isn”t a coating at all – it”s stainless steel,” noted Barclay Simpson, chairman of Simpson Manufacturing, a Dublin-based company that produces Strong-Tie brand wood connectors.
Stainless steel can be many times more expensive than galvanized and is not as widely used by builders.
Growing environmental and health concerns forced the wood preservative industry to stop using arsenic to treat wood for residential uses. The most common replacement preservatives are ammoniacal copper quat, or ACQ, followed by copper azole, and borate. Borate is sometimes used in home foundation sill plates, but experts say borate-treated wood is not appropriate for outdoor uses.
The higher metal corrosion rates associated with ACQ-treated wood have raised concerns with the federal Consumer Product Safety Commission.
“CPSC is recommending consumers use stainless steel brackets and fasteners in conjunction with ACQ-treated lumber,” stated commission spokesman Scott Wolfson. The CPSC is considering whether it needs to study the corrosion issue further.
Pressure-treated wood is commonly used to provide a base, or sill plate, for the rest of a structure”s framing, which is attached to that base with metal connectors and fasteners. Designed to resist rot and other forms of decay, treated wood is used in many outdoor applications, including children”s play structures, decks, walkways and fences.
The California Building Code has for years stated that “fasteners for pressure-preservative treated … wood shall be of hot-dipped zinc-coated galvanized, stainless steel, silicon bronze or copper.”
“This is an issue we have to look into,” said Bob Raymer, technical director of the California Building Industry Association, which recently began to focus on the corrosion concerns. “The fact you may have some surface corrosion raises an aesthetics problem … but that”s a far cry from actually seeing a wall falling down.” \ �2005 FastenerNews.com