Chesterfield Roofing: Article About Slate Roofing
Like any other material used as the covering for a rooftop, slate is subjected to the effects of weatherization, air pollution and exposure to organic matter such as bird droppings. Over time, these elements can have a considerable impact on the performance, lifespan and aesthetic appeal of the roofing system. Experienced Chesterfield roofing contractors will inspect slate roofs to identify and fix these issues before they have a chance to become major problems.
Occlusions are a common problem for slate tiles. They are the result of mineral impurities that occur naturally in a vein of slate rock. Iron and carbon are the most common types of impurities that cause an inclusion in slate. They create rusty-looking stains on the roof's surface. The occluded area is a weak point where a tile can start to split or flake after years of exposure to rain, ice, snow, sunlight and wind.
The cleavage plane of slate tiles is another area that roofers must inspect. If too large of a piece splits off a tile, the section can become too thin to provide adequate protection from water intrusion. When a large section of stone separates, most roofers will replace the individual tile.
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In some cases, a tile can be damaged at a cleavage plane during installation. Simply driving a nail through the tile could split it. Such tiles should not be installed on a roof.
Delamination is another common concern for slate tiles. In the delaminating process, minerals in the stone react with oxygen and other elements in the air. Changes in the arrangement of the minerals cause expansion in the space between atoms of the rock. This results in thin layers of the slate flaking off. Over the course of several years, the interior of the stone loses strength and becomes soft and spongy. Once this happens, the stone begins to absorb even more water, and splits in the tile become more likely. Delaminated tiles are a point of failure for many slate roofs.
Efflorescence can also occur on slate. Ultraviolet radiation from the sun combines with moisture to cause calcium and other minerals in the slate to dissolve. As this happens, the slate becomes increasingly porous. The loosened minerals slide down the tiles and become distributed as white streaks that run down the roof. If the efflorescence is widespread around the sloped sides of a slate roof, this suggests that the roof has a drainage problem. Correcting the drainage problem should help to prolong the roof's life.