Feature Photo ©Dreamstime.com Specifying Rock & Slag Wool Insulation By Angus E. Crane M ineral wool, rock, and slag wool insulation provide thermal, acoustical, and fire resistance, while simultaneously saving energy and reducing pollution.1 However, unlike many other building materials with innovative, green properties, the material is neither particularly complex nor new to the industry. In fact, early uses of this type of insulation trace back to the Hawaiian Islands, where huts were blanketed with fibrous wool after being collected from volcanic deposits where steam had “broken the molten lava into fluffy fibres.”2 Mineral wool was commercially produced for pipe insulation in Wales in 1840, and in the United States 35 years later. In 1897, C.C. Hall, a chemical engineer, produced rock wool; only a few years later, the product was manufactured commercially at a plant in Alexandria, Indiana.3 Slag wool production in Europe began in the 1880s using various types of slag, a material formed during the reduction of iron ore to pig iron. After the Second World War, most plants began instead employing rock as the raw material. While most European plants still melt rock, North American facilities continue to rely on slag as the principal ingredient, along with rock, limestone, clay, and feldspar. Produced from basalt and industrial slag, modern rock and slag wool insulations are high-tech versions of their predecessors. These insulation products provide established thermal, acoustical, and passive fire protection properties. Production and composition Rock and slag wool insulation comprise basically the same raw materials (but in different proportions) and are produced in the same way. Manufacturers use a mechanized process to spin a molten composition of rock and slag into high-temperature-resistant fibres. Their similar properties also produce similar performance attributes—the major difference is in the specific volumes of the various raw materials utilized to make each product. Typical modern rock and slag wool are composed of calcium magnesium aluminum silicate. They are produced by melting a mixture of various slag and/or rock raw materials in an electric or gas-heated furnace or a coke-fired cupola. For rock wool, the procedure is carried out using a mixture of various natural and synthetic rock sources to yield the desired composition. In the manufacturing of both rock and slag wool, one raw material is normally the main component, with other ‘ingredients’ added to make up for a particular deficiency in the original raw material. For example, if the main component is too rich in acid oxides (e.g. silica), then limestone or a slag rich in calcium oxide is added. In slag wool production, iron-ore blast-furnace slag is the primary component; in rock wool production, it is usually basalt. For rock and slag wool produced from materials melted in a cupola with coke as fuel, all iron oxide is reduced to ferrous oxide. 30 January 2010 Construction Canada CC_JanFeb10.indd 30 12/22/09 11:55:48 AM