Corrosion of Welded and Chromated Galvanized Lath Reinforcement in Cement Stucco

Abstract

The purpose of this report is to compare the corrosion resistance of several proprietary combinations of stucco and wire reinforcing mesh (lath) to enhance corrosion protection against chloride environments. The lath is produced by spot welding galvanized steel wire and was tested pre-welding, post-welding and after a post-weld chromate treatment. The effect of the weld joint and the chromating on the initial rapid corrosion, typical of zinc embedded in cement-based materials, was first investigated. Despite the loss of zinc at the welds, there was little difference in corrosion rates of the non-welded and welded specimens. The chromating, however, was found to be highly beneficial in eliminating the initial rapid corrosion. A second set of tests investigated the comparative corrosion behavior of the lath in OPC-based stucco and a commercial calcium-aluminate-based stucco (Stucco A) in chloride solution. The study showed the Stucco A to provide less protection than the OPC stucco. Addition of lime to Stucco A, which is not recommended by the manufacturer, resulted in greater corrosion protection.