Steel is an abundant, efficient building material that provides specifiers design freedom. However, for projects exposed to the atmosphere and other harsh environments, it is critical to coat the steel for corrosion protection. Often large construction projects target a 50-100 year design life, highlighting the need for durable, long lasting corrosion protection. Hot-dip galvanizing (HDG) provides three levels of corrosion resistance to steel: barrier protection, cathodic protection, and the zinc patina.
Hot-dip galvanizing, like other coatings, isolates the steel from the environment providing basic, barrier protection. The intermetallic layers of the zinc coating are tightly bonded (~3600 psi) to the base steel making damage difficult. Galvanizing also provides cathodic protection, meaning the zinc will sacrifices itself to protect the underlying steel. Even if the coating is scratched, the surrounding zinc will continue to resist corrosion of the steel.
In addition to the barrier and cathodic protection, hot-dip galvanizing has a third level of protection the zinc patina. As zinc is exposed to the environment, it naturally forms by-products on the surface which slows the corrosion rate and acts as an additional environmental barrier. When the zinc patina is fully developed, hot-dip galvanized steel will corrode at approximately 1/30th the rate of steel in the same environment.