The steel sheets used for building applications are corrosion protected with metallurgical coating of 180 GSM to 275 GSM galvanising. "Zincalume" "Galvalume" sheets have metallurgical protection of 55% hot dipped coated Aluminium, 43.5% Zinc and 1.5% silicon. The coating density these is either 150 GSM or 200gsm. The Zinc - Aluminium alloy coating provides excellent corrosion resistance coupled with sacrificial protection provided by the Zinc in the alloy.