Corrosion behaviour of mortar embedded wall-ties in natural and artificial environments

At present metallic wall-ties for use in masonry veneer and cavity wall construction are classified according to their level of corrosion resistance. This durability classification is based on short-term artificial salt spray testing according to Australian Standard AS 2699.1:2000. Previous studies have shown that the corrosion process changes with time. As a result, long-term durability predictions based on short-term results present a challenge for extrapolation. Moreover, the relevance of artificial environment simulations used for extrapolating equivalent long-term field exposure loss predictions also has been questioned. This study reports one-year test results from an empirical testing program currently in progress, and which tracks corrosion damage for several permutations of wall-tie durability class materials and mortar mixes exposed to both natural and artificial salt spray environments. The preliminary results indicate differences in corrosion behaviour of galvanized and stainless-steel ties. They also indicate differences between exposure conditions, with causality attributed to potential mortar atmosphere-interface conditions. The likely reasons for these observations and the potential practical implications are explored and discussed.