Zincalume is a proprietary BlueScope Steel coating: 55% aluminium and 45% zinc applied to mild-steel sheet in a continuous coil-coating process. The aluminium provides barrier protection, the zinc provides sacrificial protection, and the combination outlasts plain hot-dip galvanising in most non-marine environments by 2 to 4 times.
Zincalume is the substrate for Colorbond pre-painted sheet (Zincalume + paint = Colorbond). Bare Zincalume sheet is also stocked for rural and shed applications where the natural silvery finish is acceptable.
Limitation: Zincalume reacts with wet concrete and unseasoned timber, both of which can corrode the coating. Don't run Zincalume gates or panels into wet concrete or against fresh treated pine without a barrier.