One of the delights of slate roofs is their great variety, each one bearing the mark of a particular quarry. Slate was used by the Romans, but it was not until markets expanded along coastal trading routes in the 16th century that the occurrence of slate was anything but very local to its source.
With the coming of the canals and railways, massive quantities began to be transported across the country, the greatest source being Wales. At their peak, the annual output of the Welsh quarries was 450,000 tons; now it is about 52,000. The other main British slate quarries are Westmorland (producing a greenish slate), Lancashire (Burlington Blue Greys), Leicestershire (Swithland-purple, grey and green), and Devon and Cornwall (grey). The famous Scottish quarries (closed since the 1950s) were Ballachulish (smaller, chunkier slates, like oyster shells, in variegated greys) and Easdale (softer, in greens and purples).
Tain-based slater Barney Livingstone has worked on many important buildings in the north, such as Eilean Donan and Ballone Castles and Fearn Abbey. After learning his trade as an apprentice, he was a general foreman before starting his own business 22 years ago. He now has several employees and two apprentices.
The ratio of repair work to new roofing is about 60:40, and the firm does many detailed jobs, including slating round a new dormer or chimney. ‘A slater needs many skills,’ says Mr Livingstone. ‘We do roof leadwork and fit rainwater goods.
‘Everything is done on site. Stripping a roof, you usually lose a third of the slates, so you have to source replacements from elsewhere, which are often secondhand. You mix them in with the salvaged slates, grading them into sizes as you dress them.’
Dressing involves trimming the slate and putting in the nail holes. Welsh and English slates have long been segregated into regular sizes, but the best Scottish slates, from Ballachulish, vary in thickness and size, requiring greater skill. They are laid in diminishing courses (well suited to the steeper roofs in wet areas). Their thicknesses must be matched by the slater as he works, producing the rippling contours characteristic of many traditional Scottish roofs. ‘There’s nothing more pleasing to the eye than a Ballachulish slate roof laid properly,’ says Mr Livingstone.
He uses quite a lot of Welsh slate. These are easier to work with, being all one size, but they have to be graded into different thicknesses, which are then laid in courses with the thicker ones at the bottom (great for strength in wind and snow). Blacker Spanish slate, although poorer quality, is also used, particularly for new work?’we have to be competitive in pricing’.
Slates are applied from the bottom up, the ridge (which might be finished in lead, fireclay or sandstone) and chimney flashings being done last. In England, slates are laid over battens, but in Scotland, roofs have been decked with sarking boards laid across the rafters since about 1800, which increases their strength, insulation and water resistance. Traditionally, slates had one nail and were bedded in lime to keep them firm and stop slippage. Now they are laid over a breathable felt membrane and fixed with two copper nails.
Slate is long-lasting and recycleable. ‘It’s the fixings that perish, necessitating reslating, but a well-slated roof, properly maintained, should not need redoing for well over a century.’
Barney Livingstone?01862 893518