Since the phase-out of CCA-treated lumber, concerns have surfaced regarding the higher corrosivity of alkaline copper quaternary (ACQ)—one of the most common new preservatives in use—and its potential effect on some fasteners. The industry has acknowledged that ACQ is more corrosive than CCA, but there is no generally accepted measurement of how much faster corrosion occurs in ACQ lumber.
“[Predicting] corrosion is a technically complex matter,” says John Kurtz, executive vice president of the International Staple, Nail and Tool Association (ISANTA), especially when you try to predict the corrosion rate of all the fasteners available on the market in any given environmental situation in combination with any ACQ formulation.
Although manufacturers tested their fasteners and connectors to determine corrosion rates,it is important to understand that there is no standardized method to evaluate a fastener's resistance to wood preservatives. Manufacturers use different types of general corrosion tests, such as ASTM's salt-spray test, but none actually gauge a fastener's reaction to wood preservatives. Some industry organizations are working on developing a test method that could be accepted industry-wide and incorporated into building codes.
Until some of the questions are answered, dealers should ensure they are selling the correct fasteners with the new lumber, and they should check with their fastener and connector vendors, most of whom are making product-specific recommendations. Some, however, defer to the recommendations of wood-preservative and treated-wood producers. Nearly all acknowledge that Grade 316 stainless steel provides the maximum amount of corrosion resistance possible.
At a minimum, hot-dip galvanized fasteners are recommended for use in non-coastal applications of treated wood, but they are not all the same. “When a recommendation is for hot-dip galvanized connectors and fasteners, it needs to be more specific. You need to give an indication of how thick that galvanizing needs to be,” says Mark Crawford, manager of engineering for Simpson Strong-Tie. Wood treaters specify that hot-dip galvanized fasteners should meet ASTM A153 and connectors meet ASTM A 653 Class G185.
Several manufacturers also offer triple-coated zinc polymer fasteners that are not addressed by building codes, but have been tested for corrosion resistance.
ITW Buildex: Dec-King Climacoat exterior wood screws;
PrimeSource Building Products: PrimeGuard Plus coated fasteners;
GRK Canada: Climatek coated screws;
Grabber Construction Products: GrabberGard Exterior Wood fasteners;
Starborn Industries: Deckfast coated fasteners;
Stanley-Bostitch: ThickCoat electrogal-vanized nails;
Maze Nails: Double hot-dip galvanized Stormguard nails;
Fasco America, Senco, and Swan Secure Products: Grade 304 and 316 stainless steel fasteners
Simpson Strong-Tie: ZMax G185 hot-dip galvanized connectors
USP Structural Connectors: Triple Zinc G-185 hot-dip galvanized connectors;
Paslode: Hot-dip galvanized nails;
Powers Fasteners: PTZ Powder Actuated Fasteners.
Manufacturers remind users that despite recommendations, there is no way to predict the actual service life of any fastener.
“Treated lumber in most applications has quite an extended life expectancy, and none of us in the industry can say with absolute certainty what will happen to fasteners, joist hangers, and other hardware five, 10, or 20 years down the road,” acknowledges Kim Pohl, marketing director for Maze Nails. “We simply don't have the years of experience with the new treatment alternatives that we had with CCA.”