Zinc rich primers are used to protect steel surfaces from corrosion. They provide this corrosion protection by electrical means. The zinc and the steel combine for a tiny electrical - cathodic cell that protects the steel at the expense of the zinc. The zinc primer will also provided a little barrier protection as well.
It is intended for structural steel members and not for thin-gauage metal sheets. Also, the primer must be in intimate contact with the clean metal, otherwise it will not provide cathodic protection to the metal.
