Then along came ZINCALUME®, a high tensile roofing product that revolutionised the roofing industry, it was strong, came in long one-piece sheets that reached from the roof ridge to the gutter without a join.
The emergence of ZINCALUME® (primarily a zinc and aluminium mix of metals "galvanised" to steel) as a popular roofing material brought problems for the trusty galvanised water tank. In the early days there were instances where new ZINCALUME® roofs were installed and within months the galvanised water tank had rusted out. The tank would break out in brown freckles and in a short time the freckles would begin to join up and the tank would collapse and the owners would then realise that the freckles were rust. The freckles/rust were caused by electrolysis. Electrolysis is a result of metals of opposing make up being joined together, in this case with water, which then creates an electrical field like a battery. The electrolytic action corrodes away the less noble of the two metals and in this case the galvanised tank.
Nowadays electrolysis is still possible where a building still has a galvanised (zinc) roof which supplies water to a ZINCALUME® tanks.