Slate in buildings
Slate can be made into roofing slates, also called roofing shingles, installed by a slater. Slate has two lines of breakability: cleavage and grain, which make it possible to split the stone into thin sheets. When broken, slate retains a natural appearance while remaining relatively flat and easily stackable.
Slate is particularly suitable as a roofing material as it has an extremely low water absorption index of less than 0.4%. Its low tendency to absorb water also makes it very resistant to frost damage and breakage due to freezing.
Slate roof tiles are usually fixed using either nail fixing, or the hook fixing method as is common with Spanish slate. In the UK, nailing is typically done with double nails onto timber battens (England and Wales) or nailed directly onto timber sarking boards (Scotland and Northern Ireland). Nails will traditionally be copper, although modern alloy and stainless steel alternatives are known. Both these methods, if used properly, will provide a long-lasting weathertight roof with a typical lifespan of around 80–100 years.
Some mainland European slate suppliers suggest that using hook fixing means that :-
- Areas of weakness on the tile are fewer since no holes have to be drilled
- Roofing features such as valleys and domes are easier to create since narrow tiles can be used
- Hook fixing is particularly suitable in regions subject to severe weather conditions since there is a greater resistance to wind uplift as the lower edge of the slate is secured.
The metal hooks are, however, visible and may be unsuitable for historic properties.Slate tiles are often used for interior and exterior flooring, stairs, walkways and wall cladding. Tiles are installed and set on mortar and
grouted along the edges. Chemical sealants are often used on tiles to improve durability and appearance, increase stain resistance, reduce efflorescence, and increase or reduce surface smoothness. Tiles are often sold gauged, meaning that the back surface is ground for ease of installation. Slate flooring can be slippery when used in external locations subject to rain. Slate tiles were used in 19th century UK building construction (apart from roofs) and in slate quarrying areas such as Bethesda, Wales there are still many buildings wholly constructed of slate. Slates can also be set into walls to provide a rudimentary damp-proof membrane. Small offcuts are used as shims to level floor joists. In areas where slate is plentiful it is also used in pieces of various sizes for building walls and hedges, sometimes combined with other kinds of stone.
Due to its thermal stability and chemical inertness, slate has been used for laboratory bench tops and for billiard table tops. In 18th- and 19th-century schools, slate was extensively used for blackboards and individual writing slates for which slate or chalk pencils were used.
In areas where it is available, high-quality slate is used for tombstones, commemorative tablets and by artists in various genres.