Question
I am installing some wrought iron fence.  What is the difference between galvanized posts verus zinc coated posts?

Answer
While this is really not my area of expertise I will try and tell you want I know.

What is the difference between zinc and galvanized? Both zinc plating and galvanizing applies a zinc plating. So they both use zinc. The big difference is in thickness, zinc plating is typically 3 microns thick. Hot dip galvanizing is 50 microns thick - so you get 10 times the protection with galvanizing.

Even after 20 years outdoors this galvanized fence shows no signs of rust. The Galvanizing has formed a white protective coating (patina) that adds to its protective properties.

All true galvanizing is hot dip galvanizing. The term "hot dip galvanizing" is used so there is no confusion over some paint companies who try to full the consumer by calling their product "galvanizing". Parts to be galvanized are submerged in molten liquid zinc, hence the name "hot dip."

Hot-dip galvanizing is a form of galvanization. It is the process of coating iron, steel, or aluminum with a thin zinc layer, by passing the metal through a molten bath of zinc at a temperature of around 860 癋 (460 癈). When exposed to the atmosphere, the pure zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), which further reacts with carbon dioxide (CO2) to form zinc carbonate (ZnCO3), a usually dull grey, fairly strong material that stops further corrosion in many circumstances, protecting the steel below from the elements. Galvanized steel is widely used in applications where rust resistance is needed, and can be identified by the crystallization patterning on the surface (often called a 搒pangle?.

Hope this helps.

Sean J Murphy
Director
B+C Studio
http://www.bc-s.net
also see my blogs at http://www.seanjmurphy.com
and http://www.amenityarchitects.com