A durable layer of zinc coats the steel and forms a physical shield, or barrier, from environmental elements. A tough atmospheric layer of zinc carbonate is formed at the surface of the galvanized coating when exposed to typical atmospheric conditions. The zinc carbonate is microscopically thin and is insoluble.
Insolubility makes the surface weather resistant and minimizes corrosion.
Zinc reacts with oxygen to form a very thin, hard layer of zinc oxide. When this surface has access to freely moving air in normal atmospheric exposure, the surface reacts with rainfall or dew to form zinc hydroxide. As the surface dries the zinc hydroxide reacts with the carbon dioxide in the air and is converted to basic zinc carbonate. Steel and zinc both react with the environment, but zinc reacts slightly faster. When exposed to the environment, zinc reacts first, and leaves the steel unaffected - that is, the zinc is sacrificed to protect the steel.