| Roofing Materials. Iron and steel, in the form of thin sheets, are used for roofing. In making these sheets, great care is used to obtain a product that will resist the tendency to rust, and that will have the necessary toughness and ductility (ability to be bent without cracking) so it can be worked into the shapes required in roofing. Some manufacturers claim to get the best results by making a very pure iron, while others believe that better qualities are obtained by mixing in small quantities of certain other metals, such as copper and manganese. Whatever the materials, the mixture must be uniform in composition, compact in texture, and free from isolated particles of foreign material that may prove to be points of weakness, or starting points for rust or corrosion. |
Black, or plain, sheets are sometimes used, although more commonly the sheets are galvanized. Galvanizing is a process of covering iron or steel plates with zinc, for the purpose of preventing rust that takes place when iron or steel is exposed to the weather. Gauge of Metal. |
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