Durability of Slate Tile

Welsh Slate

• The oldest slate quarries in the world are found in Wales. The geologic conditions in Britain make the quality of the Welsh slate superior. Welsh slate is respected because of its composition. It has a low organic content, is resistant to acid rain and alkali, it does not fade and water does not penetrate its surface. Extreme weather conditions do not harm Welsh slate. Used as a kitchen counter, it is resistant to heat. Welsh slate has been found on buildings over 400 years old, and was used on Buckingham Palace and Number 10 Downing Street.

United States Slate

• Slate is still mined in several states along the eastern coast of the United States: Vermont, New York, Pennsylvania, and Virginia. Vermont green slate has been known to last over 120 years, but a building with a roof of Pennsylvania black slate mixed with Vermont green found the black slate deteriorating after 120 years. Pennsylvania slate may lose its color and wash from blue-black to brown or gray. Some Vermont slates loose color. New York red slate is dry and brittle. Virginia slate has a mica sheen. While American slate may not be as durable as Welsh slate, American slate tile is considered to last a lifetime.

Spanish Slate

• Spain's far northwestern region of Galicia is the largest producer of roofing slate. The British Standards Institute has instituted a quality control marking, CE, that is received when a product produced in Europe is prepared for export. If you are purchasing a Spanish slate, be sure it has the CE mark. The Spanish slate is being closely monitored in Great Britain as to its durability in the British climate. Already one shopping center in London with a Spanish slate roof has had to replace the roof.

Chinese Slate

• Although Chinese slate has been used in the country for over 500 years, it has only recently entered the international market. Some of the Chinese slate has been known to fade, absorb water and to have issues with acid resistance. Slates from several mines are shipped in one lot, meaning various characteristics of the slates are put together in a single order. This results in an uneven wearing of the slate. Chinese slate can also become soft and delaminated, able to be crushed by the hands.