Until recent decades, a common material for steel roofs, sheds and rainwater tanks the littered the Australian outback were galvanised iron – steel that has a zinc coating to provide protection against rust and corrosion.
Prior to 1976 many steel roofs were also galvanised. Then BHP Steel (now BlueScope Steel) developed and launched ZINCALUME® steel which possessed a higher level of corrosion resistance. It has since become the number one choice in steel roofing, cladding and construction in Australia.
Instead of the traditional zinc coating found in galvanised steel which provides electrochemical protection, research and tests found steel dipped in aluminum (55%), zinc (43.5%) and a bit of silicon (1.5%) protected the steel base in two ways. It provides a tough physical barrier to protect the inner core steel against the weather, and secondly it protects the steel if cut at its edges and scratched. In effect, this provides much better protection against rust and corrosion.
In August 2013, BlueScope Steel released next generation ZINCALUME® steel. This introduces magnesium into the mix, resulting in an even tougher protective coating that’s more resistance to scratches and scuffs encountered during construction.
Compared to the older ZINCALUME® steel (AZ150) which has a roofing warranty of up to 25 years against weathering, next generation ZINCALUME® steel (AM125) carries a warranty of up to 36 years. For further information comparing the two ZINCALUME® steel products, read BlueScope’s Product Release Guide for Next generation ZINCALUME® steel.
While ZINCALUME® steel has demonstrated superiority with roofing and wall panels, when used to store rainwater they face several weaknesses and may not last much longer than a more thickly coated galvanised tank. For this reason perhaps, it is important to note that BlueScope themselves recommend their AQUAPLATE® steel product for rainwater tanks, which is a steel that is coated with a 0.2mm poly coating on the inside to help protect against corrosion.