What types of salt spray ratings do Hot Dip Galvanized coatings get?
The hot dip galvanized coating does not perform well in a salt-spray test chamber. In order for the zinc in the hot-dip galvanizing to perform as it was designed, it needs to develop a patina layer composed of zinc carbonate. This layer is very stable and non-reactive which gives the galvanizing its desired properties, but in order to form this patina, the zinc must go through wetting and drying cycles such as those that would be encountered in a real world environment. In an ASTM B117 salt spray chamber, the environment is kept continuously wet which basically washes off the necessary corrosion resistant products that would otherwise be produced naturally by the galvanizing. Therefore, the hot dip galvanizing appears to have a poor salt spray corrosion resistance, but this type of QC testing isn’t really applicable for hot dip galvanized coatings.
