Do wall ties need to be galvanized in solid masonry walls? The steel used in concrete is typically not coated. Wouldn't solid masonry offer protection similar to that offered by concrete?
There is a substantial difference between the protection to steel offered by masonry and that offered by concrete. In concrete, the fluid cement paste completely covers the bars. In masonry, the steel is often dry-laid on the units and the mortar placed on the top. Therefore, the bars are not always encased completely in mortar. Sometimes there are voids along the bottom of the bars, which can allow condensation and moisture to accumulate. The corrosion potential of the steel is also affected by material porosity and diffusion rates of harmful ions (such as chlorides). Bare steel is protected initially by a passivating layer that forms in the highly alkaline environment of wet concrete or mortar. Carbonation will reduce the alkalinity of the mortar or concrete and eliminate this protection. Mortars, being more porous than concrete, will carbonate at greater rates. There is also greater potential for diffusion from chloride ions from acid cleaning or other sources. Depending on their concentration, chloride ions will eliminate the pacifying effect of the mortar. For these reasons, unprotected steel encased in mortar will have an increased corrosion potential at a young age. Requirements for concrete or mortar cover over reinforcing steel in cast-in-place concrete are greater than those for masonry wall ties, thus giving more protection. Concrete design codes require a minimum cover depth of 1 1/2 inches for #5 and smaller bars in concrete exposed to weather. Masonry wall ties, on the other hand, are required to have a minimum mortar cover of 5/8 inch. For these reasons, the bars used in clay masonry should be galvanized or otherwise protected against corrosion. Not only will the corrosion of steel embedded in masonry reduce the strength of the steel reinforcing or ties, but the expansive pressures generated by corroding steel may crack or spall the masonry.