How long will galvanized steel masonry wall ties last?
Many variables affect the durability of galvanized wall ties in masonry walls. First, ties are embedded in mortar. Uncarbonated and chloride-free mortar protects galvanized steel. But as mortar reacts with carbon dioxide from the air (rapid if the mortar is porous) or if mortar contains chlorides from admixtures or improper cleaning techniques, corrosion of the galvanizing is accelerated. Second, most ties cross an air space between the masonry and a backup. The portion of the tie within the air space typically corrodes faster than the portion embedded in mortar. The rate of corrosion is influenced by how often the tie within the air space is wet, which depends on air exfiltration, local humidities, and rainwater leakage, among other things. Corrosion is accelerated if the air is corrosive, such as in a marine or heavily industrialized environment. Finally, the life of the tie, all other factors being equal, is directly related to the thickness of the galvanized coating. With all these factors in mind, John Slater of Invetech Inc., a Houston consulting firm that specializes in the behavior of metals in structures, estimates that galvanized masonry wall ties may last 5 years or several hundred years. Many corrosion problems related to the use of galvanized ties in masonry walls have been encountered in Great Britain where most major cities are near the sea. The problems are so severe, in fact, that many experts in Great Britain recommend the use of stainless steel in all new and repaired masonry walls. For extended life or for masonry located in corrosive environments, stainless steel should be considered in the United States too. As a minimum, I recommend using galvanized ties with a coating at least as thick as required by ACI 530.1/ASCE 6, Specifications for Masonry Structures. According to this spec, sheet metal ties completely embedded in mortar or grout should have 0.60 ounce of galvanizing per square foot. Wall ties in exterior walls completely embedded in mortar or grout should have 0.80 ounce per square foot. Sheet metal ties exposed to weather and other ties in exterior walls not completely embedded in mortar or grout should have 1.50 ounces per square foot.