Slate Stone, Slate Stone Exporter, Slate Stone Supplier

Natural stone roofing provides much of the special character of many parts of the country. Stone slate roofing can still be found. However, this long-established situation could be under threat unless the production of stone slates, and the craft of laying them, is studied and revived. Even the name seems to be disputed: often called stone slates they are clearly not a metamorphic slate (such as Welsh slate) and yet neither are they tiles, in the sense of a clay moulded object.

There are, geologically, two stones from which stone slates are made, both of which are oolitic limestones: ‘Forest Marble’ and ‘Stonesfield Slate’. The methods of producing slates from these stones are quite different, making the most of their individual properties. Forest Marble is split by hand very shortly after being extracted from near the surface of the ground, usually at a small quarry. At one quarry where slates were, until very recently, made by this method, it was thought that they should only be split within a few days of being extracted, while they still retained their natural moisture, or ‘quarry sap’. Such stone slates are called ‘presents’.

Stonesfield Slate is the name generally given to frost-split stone slates. Because of its depth in the ground, the method of extraction of the slate was quite different to ‘presents’. The stone in rough block form called ‘pendle’was hoisted to the surface from stone mines, and put out in nearby fields to become ‘frosted’. As the frost gradually split the stone along the thin natural bedding planes, these being a consequence of the geological formation of the material, slaters would work to assist the splitting process. The resulting slate was much thinner and more regular than the rougher ‘presents’, and was highly prized for the most prestigious roofs, such as those of Oxford colleges. The thinner slates also afforded an opportunity for some sophistication, such as an angled dressing of the sides to provide a very slight overlap when they were laid.

The first and most obvious feature about stone slates is that, as a material produced from fissile sedimentary rock, it is impossible to supply them in consistent sizes, unlike welsh slate, a metamorphic rock, the stone breaks naturally to provide far more smaller-sized slates than large ones. Over the years, a logical way of taking advantage of this geological accident has evolved; the practise of laying slates in diminishing courses. One of the main functions of a stone roof is to throw water well clear of the wall. Before the introduction of gutters it was even more important to project the eaves as much as possible. So the largest slates (normally about 600 mm long, but some up to 750 mm long) were fixed here in a double eaves course. These slates were given a special name ‘cussoms’, the next course being called ‘followers’. The smallest-sized slates (called ‘short cocks’) were the most common, available in large numbers and used at the highest part of the roofslope. They were only 150 mm long.