Natural slate is a gem of a building material. Fireproof, water resistant, and durable, the stone has an expected lifetime of over 100 years. First used in the days of medieval castles, natural slate is a high-quality material that is a favorite for high-end projects.
Unlike many other building materials, natural slate requires only minimal processing. Quarried out of the sides of mountains with diamond-studded steel cable, slabs of slate are evaluated for quality, sorted, and sawn into smaller slabs. Due to minimal factory processing, the release of harmful CO2 emissions are essentially avoided. No chemicals are applied to the stone, and natural slate uses even less water than terra cotta tiles.
Splitting Natural Slate
These slabs of slate are then passed along to skilled craftsmen whose job is to split the stone into its finished thickness. Using a hammer and a chisel, slate is carefully split and passed along.
Being a slate splitter is more than just chiseling away at rocks. Each slab of natural slate is carefully examined to ensure the beauty and quality of this product is up to par. Prior to quarrying, the “overburden”— broken, compromised, or otherwise unusable rock— is removed. After being removed from the mountainside or tunnel, slate is then evaluated at the factory for any compromising flaws.
Problems to Look For
There are several different imperfections to look for when using natural slate— a high water absorption, which can lead to freezing and widening of cracks in the material. A low breaking strength, which will compromise slate’s legendary longevity. Too high of a calcium carbonate content will lead to pockets of “rusting”— an unpleasant, orange pigment will eventually bleed down the roof or siding structure. Slate splitters carefully examine each piece of slate and remove the troublesome pieces.
To read an interview with one of Spain’s natural slate splitters, click here.