Metal Surface Materials

Historical examples of the internal use of metal sheeting are limited. One example is the notorious lead chambers of Venice that were used for jailing particularly dangerous criminals, such as the seducer Don Juan. The lead chambers were placed on roofs exposed to the sun, making them unbearably hot during the day and terribly cold at night.

Modern metal sheeting is mainly galvanized steel, aluminium, copper, zinc and stainless steel. For internal use, stainless steel dominates the market. These products are often anodized with a thin surface layer or painted with special plastic paints, usually containing epoxy, acry-lates, polyester or polyvinyl chloride, the latter often mixed with phthalates. Copper, however, requires no surface treatment. Certain metals cannot be used together because the combination causes galvanic corrosion. For example, when mounting sheeting, iron or zinc nails or screws must not be used to fix copper, and vice versa. Rainwater from a copper roof must not be drained over iron or zinc, as the copper oxide produced will soon destroy the iron or the zinc.

From an ecological point of view, the use of metals should be reduced to a minimum. Reserves in nature are limited, and the production of metals requires high amounts of energy, usually based on fossil fuels; emissions of greenhouse gases and other severe pollutants during the production of metals are generally large.

Once installed, metal products cause few problems, but there can be a release of metal ions from external surfaces when washed by rain, which drain into the soil and ground water; lead and copper cause the most problems, while zinc can be a problem if used in large quantities. Using a lot of metal in a building can also increase electromagnetic fields inside it.

The durability of exterior metal claddings is moderate - best for aluminium and copper and quite low for zinc products, especially if exposed to sea air or polluted town air. Intact sheets can normally be re-used in their original form, but this is seldom done since they are often damaged, particularly during dismantling. The alternative would be material recycling achieved by melting them down. However, in this case there may be emissions from the coating treatments that are often applied, including dioxins from products coated with polyvinyl chloride. Powder-coated aluminium is not recyclable. Polluted and mixed waste must be disposed of at special facilities. It should not be mixed with waste for energy recycling, since the surface treatments can emit toxic gases.

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