About Slate: History, Composition and Uses
Slate is a foliated metamorphic rock which is derived from shale and consists mainly of the mineral mica. Shale is a sedimentary rock with a very complex chemical composition. Through thousands or millions of years of heat and pressure it can metamorphose into a wide range of different rocks. These can have a great variety of different chemical compositions and textural characteristics which serve to illustrate the incredible geological effects of our planet. Through a process of barrovian metamorphism, shale becomes slate, then phyllite, schist and eventually gneiss. It is incredible that all these visibly different rocks are created from the same sedimentary parent.
Visually different slates can vary considerably with most being black green or grey with more interesting examples containing reds and yellows. It is a fine grained, thin layered stone with a hardness rating of 2.5-4 on Moh’s scale, meaning it is easily scratched. It is sourced from many different countries with some of the best slates coming from Brazil, Portugal and Wales.
- Traditional roofing material: Slate roofs have been known to last hundreds of years
- Flooring tiles: Typically paving stones outdoors and kitchen/bathroom tiles indoors
- Jewellery, Coasters and Candleholders
Restoration and Maintenance:
It is important to understand the stone maintenance cycle in order to properly maintain the beauty and lustre of your natural stone installation.
Slate can be well maintained if a proper maintenance cycle is put in place from the point of installation. Due to the lack of calcite in its composition, slate is resistant to acid. Problems can still arise however if the slate is very porous, as some can be, in which case the application of a good quality penetrative sealer is an absolute must.
Any stone needs a well-planned maintenance schedule in place to preserve it and to delay restoration procedures for as long as possible. Daily maintenance will consist of dry dust mopping using a clean rayon mop. Regular damp mopping will also be required. This must be carried out using a good quality stone soap alternated with just freshwater. It is important that soap residue doesn’t build up on the surface of the stone. If the slate is honed or polished, regular professional maintenance will be required to maintain its appearance and remove any scratches or loss of shine and lustre.
Slate is a versatile stone that can be left rough, honed smooth or polished to a shine. Slate tiles can look very natural and unusual indoors however many of our clients complain of their dull coloured, ‘garden path’ appearance. In this situation, the slate can be treated with an enhancing sealer which will serve to deepen the colour without sacrificing the rough, layered texture of the stone.
Another common request is for a natural uneven slate tile floor to be made completely flat. We can achieve this using a diamond abrasive procedure which will effectively grind down the slate to a perfectly level finish. It can then be left with a mat appearance or polished to a shine as desired.