The mineral zinc occurs naturally in soil, ore, air and water. In addition to being an abundant and important non-ferrous mineral, it is also essential to daily life and promotes organ and immune system development. Asia, Australia and America are the continents from which most of the world’s zinc supply is mined.
30% of the total international zinc supply is recycled. The remaining 70% is the result of extractive metallurgy. Zinc is typically extracted as a by-product of copper, lead and/or iron, most often from deposits of sulfidic ore.
After grinding ore into a fine powder, it is subjected to froth flotation and the resulting concentrate of zinc sulphide ore is roasted. Pyrometallurgy or electrowinning follows the roasting process. The amount of energy required to produce zinc from ore is around 50% of that required for copper and steel, and around 25% of the energy required to produce aluminium.
In the mid-19th century, zinc was used to coat other metals and continues to be used primarily in galvanisation today. Zinc is used in architectural applications for rainwater systems, cladding and roofing, often as an alloy of zinc, copper and titanium. This combination of metals maximises tensile strength, malleability and load-bearing capacity.
While other metals, such as iron, suffer from exposure to water and salt, zinc forms a protective layer of zinc-hydroxyl-carbonate naturally, ensuring corrosion-resistance, UV-resistance, weatherproofing as well as earthquake-resistance.
Zinc sheeting is lightweight and formed into practical sizes for quick and easy installation. It reflects midday heat and, when used efficiently, saves on heating and cooling costs within the building. At the same time, rain or snow is shed easily from a zinc roof thanks to its hard and slippery surface when exposed to moisture.
Environmental and economic benefits
The recyclability of zinc without any negative effect on its physical or chemical properties offers significant environmental and economic benefits – of all the architectural grade zinc in production, 90 to 95% of it is recycled. Zinc’s low toxicity means that water can collect and run off roofing without contaminating soil and groundwater supply.
Zinc is attractive in its own right but can also be processed with a pre-patinated finish in a wide range of designs. Zinc roofing is effective at almost any roof pitch, and custom-shaped roofing will adhere to all manner of curvature and angling work. On the walls, zinc cladding is soft and malleable, easily formed into custom shapes. It can be manufactured smooth, weathered or patterned. Even over long periods of time, zinc roofing and cladding requires almost no maintenance.
Architects and construction experts preferred cheaper, ‘disposable’ alternatives for roofing and cladding in the 1960s and ’70s to zinc, such as asphalt shingles, which often require replacement every 10 years. Today, the trend is gradually shifting back to zinc, which is now seen as a valuable roofing and cladding material on residential and commercial architecture and construction projects and admired for its long-term durability and environmental sustainability.