Slate Roofing is a dense, durable, naturally occurring material that is essentially nonabsorbent. Two properties of slate are cleavage and fracture. It has natural cleavage, which permits it to be easily split in one direction. Fracture, usually occurring at right angles to the cleavage, is called the grain. Roofing slate commonly is split so the length of the slate runs in the direction of the grain. The surface texture of slate after being split for commercial use derives from the characteristics of the rock from which it was quarried. Some slate splits to a smooth, practically even surface, while other yields a surface that is rough and uneven.
The color of slate is determined by its chemical and mineral composition. Because these factors differ in various regions, Slate Roofing can be obtained in a variety of colors. In addition, exposure to weather causes slate to change color. The degree of change varies depending on the slate. Slate exhibiting minimal color change is known as “permanent” or “unfading” slate. The slate that shows a more marked color change is known as “weathering” slate. Between unfading slate and weathering is “semi weathering” slate roofing.
Slate is a rock, it is fine-grained crystalline rock metamorphosed from bedded deposits of clay and silt. There are three kinds of slate: mica, clay and igneous. Mica is the only kind used for slate roofing. Slate roofing has been used as a roofing material in Europe for hundreds of years with examples dating all the way back to the 8th Century. From the 17th to the 19th Century most slates in America was imported from North Wales. The first United States commercial slate quarry opened in 1785 in Peach Bottom, Pennsylvania, and the slate business in the United States was very limited and localized until the latter 19th Century. The industry grew because of population, quarrying technology, rail system and immigration of Welsh slate workers. After the Civil War, the United States became a slate exporter and slate reached its peak in the U. S from 1897 to 1914. From that time period on the slate was replaced by cheaper alternatives for roofing options but the slate is still produced and used today, there are houses that were roofed with slate in 1914 that still have the same slate roof on it today. Slate roofing materials come in a wide range of colors including black, gray, blue-black, purple, green, sea green and red. Slate roofing can be unfading in color or fading which means it changes with the weather. In the United States slate used for slate roofs comes from five main slate producing regions – Monson, Maine, Vermont, New York, Eastern Pennsylvania, Peach Bottom, Pennsylvania and Buckingham, Virginia. Outside the U.S slate is produced in Canada, Europe, China and South America. The quality can range from poor to excellent.
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