“BRANZ is currently recommending that for both 15- and 50-year situations where CuAz- and ACQ-treated timbers are used, the fastener material of choice, including nails and screws, should be either: 304/316 grades of stainless steel, or durable equivalents, such as silicon bronze”

“In the past there have been timber fastener durability concerns with the use of new high copper treatment options as an alternative to the traditionally used CCA treatment (refer to Build magazine February/March 2007). In that article it was recommended to use stainless steel fasteners or durable equivalents such as silicon bronze, when using these new treatments in timber exposed to the weather.

This led to the Department co-sponsoring further research. BRANZ is now publishing details of this three-year study confirming that significant corrosion rates are being experienced by both mild steel and galvanised nails and screws used as fasteners in Copper Azole (CuAz) or alkaline copper quaternary (ACQ) treated timber (refer to Build article August/September 2009).

We recommend the use of 304/316 grades of stainless steel or durable equivalents such as silicon bronze for all timber fasteners, including nail plates, bolts and nails, for all CuAz or ACQ treated timber exposed to the weather. The research confirms the corrosion concerns that initiated the study. The Department’s recommendation endorses that made by BRANZ in the Build February/March 2007 edition and confirmed in the recent Build publication.”