Natural slate, natural beauty

Allan Liddell of Cupa Pizarras explores the inherent beauty, as well as the environmental credentials, of natural slate

Slate is formed through the regional metamorphosis of mudstone or shale under low-grade conditions. This happens when shale or mudstone is exposed to heavy pressure and heat from tectonic plate activity, which metamorphoses its clay mineral components into ‘mica minerals’. These are the main components of slate, and determine the colour, depending on the minerals and the amount of them within any given location. These mineral components vary greatly from location to location which is why different quarries will produce different coloured slate, offering architects a palette of beautiful, natural tones. As a 100 per cent natural material, slate is a sustainable choice. Independent studies, such as one carried out by the Inventory of Carbon and Energy (ICE, University of Bath), have confirmed that it is the material with the least negative effects on the environment. Unlike other materials and roofing adhesives that leave volatile organic compounds (VOC) in the air around the building for years after being installed, natural slate uses only water in the production process. We have taken this one step further as recycled water from a closed circuit is used, to prevent water wastage and further minimise the environmental impact. Furthermore, the extraction of slate, if done correctly, can have a minimal effect on its surrounding environment. For instance, most manufacturers, as part of the production process, will conduct geological, mineral and geotechnical surveys and sample testing. This is to determine the quality of the slate and the potential reserves of the deposit, so only high quality slate is extracted. Once the reserves of slate have been exhausted, the quarries can also be restored by hydro-seeding native plants, which will ensure the natural recovery of the local flora and fauna.

Slate’s unquestionable beauty, structural quality and environmental credentials mean it is often the preferred choice from a design stance. For instance, a private residential, new-build in Cambridgeshire recently required a circular roof to accommodate the property’s shape. 12.5 metres in diameter – with a circular, 30º pitch meant the project required a durable product that could easily be cut. Starting with 24 inch x 18 inch slates at the eaves, working up the roof with 20 inch x 15 inch and then 24 inch x 12 inch, the project was finished using 20 inch x 10 inch, which were cut down in width at the top to create a distinctive yet beautiful design. Although slate is often associated with heritage projects, its versatility is increasingly seeing it contribute to more contemporary aesthetics more and more. The product can also be used as a rainscreen cladding system, to great effect, due to its naturally waterproof properties, lightweight design and aesthetic appeal. For example Split House, a private new build residence on the Sussex coastline boasts a beautiful facade on its second storey to resemble something similar to a sundial. Due to the angles of the build and the slates’ almost reflective surface, the sun could be expressed across the building with the cladding catching the light at certain angles, which created astonishing results in relation to colour movement throughout the day. Although slate has a long and established history as a building material, its design possibilities and environmental credentials enable it to be a modern choice for a wide range of projects. Extremely versatile, the use of slate is already evolving to meet changing design requirements and with research continuing to uncover new ays for this material to be used its place across the architectural spectrum seems to remain cemented.

Allan Liddell is specification sales manager at Cupa Pizarras