New Wood Treatments and Fastners - Understanding the Issues

Metal connectors, anchors, and fastners will corrode and lose load-carrying capacity when installed in corrosive environments or exposed to corrosive materials. There are many environments and materials that may cause corrosion including: salty ocean air, treated wood, fire retardant treatments, and dissimilar metal materials (stainless steel and galvanized steel used together). The many variables present in a single challenge course or climbing tower project make it impossible to accurately predict if, or when, significant corrosion will begin or reach a critical level. This relative uncertainty makes it crucial that all challenge course builders be knowledgeable of the potential risks and select a product coating or metal fastener that is suitable for the intended use.

Changes in the preservative-treated wood industry have created additional concerns. Effective December 31, 2003, the preservative-treated wood industry voluntarily transitioned from Chromated Copper Arsenate (CCA) used in residential applications to alternative treatments. CCA will continue to be used to treat wood for industrial, commercial, and agricultural uses. In addition, existing inventories of CCA-treated wood produced before January 1, 2004 can be sold into the residential market until exhausted.

Testing has shown that certain alternative replacement treatments are more corrosive than CCA. The treated wood industry has recommended the use of stainless steel or hot-dip galvanized fasteners and connectors for years. This recommendation is still the same for use with the alternative treatments, but additional clarification is needed to ensure that adequate corrosion protection is provided. Specifying hot-dip galvanized products is often very generic and not enough. More specifically, when working with new treatments Amine Copper Quat (ACQ), Copper Boron Azole (CBA), Copper Azole (CA), etc., stainless steel should be used wherever possible. When not possible, a "double-dipped" galvanized fastener should be used. Galvanized fasteners have a rating. While a G60 (which means .6 oz per foot of galvanization) has proven appropriate and effective for use in CCA-treated wood, the new treatments (ACQ, CBA, CA, etc.) can be twice as corrosive as CCA. Thus, fasteners with a minimum rating of G90 or a preferred rating of G185 should be used if using galvanized fasteners in these new wood treatments. 304 and 316 stainless steel fasteners, while a tad bit more expensive, are superior to any galvanization process in performance tests in all types of treated woods.

In conclusion, due to the wide availability of various wood treatment products throughout the world and an even larger variety of fasteners to choose from, it is critical that builders match fasteners and treatment types for the long term sustainability of their products and ensure the fasteners being used are manufactured for and approved for use in the type of wood treatment being used. When in doubt, contact the manufacturer or look for labels on the fasteners that state they are approved for use in the particular type of wood treatment being used.