Slate expectations: traditional roofing material


Damage to roofs caused by poor air quality and central heating means plenty of restoration work for Nigel Smith’s company.

Smith in his workshop © Tim George Nigel

The village of Collyweston is surrounded by great slopes of stone. This part of England — near Stamford, where Lincolnshire meets Northamptonshire — is the old haunt of Collyweston slaters, and the nicknames for the variously sized stone slabs remain a lexical wonder of the region. Mumfords and mopes, wibbets and outrules: the Mary Poppins-like patter of the slaters is seldom spoken now. Few today want to pay a premium for traditional materials — even if they could get them — when Chinese slate is cheaper.

Yet that might change as some are trying to rescue the traditions of English stone roofing. Nigel Smith grew up in Stamford and has lived there for almost 50 years. His great-grandfather, Willie Smith, was a Collyweston slater, talking of longbacks, even-mopes and in-bows. After an interlude for the second world war, Smith’s father, Claude, re-established the family business in 1965.

The Anglo-Saxon town of “Stone-ford” lies at a crossing of the river Welland. Almost all its historic buildings are composed of limestone walls and roofs gleaned from the surrounding hills, their soft contours formed by prehistoric marine organisms that rolled under a shallow warm sea about 180m years ago. Seams of sand and clay were laid down as the aeons passed, which compacted into a stone that would split like slate, especially that under Collyweston.

By the 17th century the land around Collyweston was owned by the Cecils of Burghley House, a vast Elizabethan pile. The Cecils parcelled their land into strips for entrepreneurial miners. Mining for the slate throughout the east of England hit its peak in the late-1800s. The “logs” of slate were extracted in the autumn after the agrarian harvest. Strong-armed labourers could then turn from scythes to stone axes, from building fences to hammering in props.

High Street, Collyweston, with roofs from local slate © Tim George

Collyweston slate is indeed mined, not quarried, and reached by a shaft or horizontal adit. The shaft is no more than 1.5-metres tall, so standing up was always difficult. But a judicious swing of a pick can dislodge a “log” of stone from the earth — at the most, about 75cm long and 20cm deep, to be hauled out by hand or horse.

The labourers would lay them on the wet ground to await the frost. A freezing dusk under a clear sky promised morning sun and, sure enough, the ice in the clay-rich bands expanded, forcing open the stone. Over the course of weeks or months, this cycle of freezing and thawing would gradually widen the gaps until the log fractured into sheets of light umber. The rest was done with a cliving hammer to knock precisely where the stone split into a slate of the right thickness, then the edges were trimmed into the closest size from an outrule — anything less than 6in — to a 2ft “long 10”. With a drilled hole ready to hang them from chestnut battens, they were good to go. And so it was for centuries.

Restoration of the Collyweston slate roof at Oakham Castle, Rutland © Tim George

But few now can recall the last winter cold enough for the freeze-thaw action to naturally split the stone. One writer, Alec Clifton-Taylor, claimed it was 1969. The slates became rare commodities, sometimes stolen to order from barns when few could afford or find them. Burghley House kept its own stockpile, as well as a small mine, and employed slaters and labourers like Laurence Porter, who has spent 35 years repairing its roofs. But it was the exception.

At Collyweston, things are changing. Smith owns a hectare of land with an old mine, which his father bought in 1989 but never exploited. Smith has ordered industrial freezers to split the logs (preparing for delivery even as these words are being written) and with them he says this summer will start to yield a 10-year supply at 200 tonnes of slate a year.

Some of the slates will be for new work. Smith says slaters have styles with a personality that is welcomed, as characterful variations deny any sense of dull regularity. But he adds that much of the supply of stone sheets will be for restoration work — he has noticed a big difference in the state of preservation in towns and villages. “In the villages, about 30 per cent of the slates can be salvaged for re-roofing. But in towns, the loss is more like 80 per cent. That’s got to be down to air quality — the air’s pretty clean in the villages, so there’s moss on the slates. Not in towns. You can often poke your finger through old slates.”

At Cambridge university’s King’s College it is the central heating that is to blame. “Condensation has eaten away at the underside of the slates,” says Smith. In 2018 he will replace 15,500 sq ft of roof slates. Meanwhile, he suggests, rather than pump up the temperature, we should put on another jumper.

Smith inspecting the Collyweston slate seam © Tim George

The past half-century of unseasonal heating and air pollution has wreaked havoc on slates that should easily last a century or more. Responding to the destruction with enterprise may well be the opportunity for a new era, a reinstatement of a living tradition of beautiful roofs. Bring on the wibbets.

Source : Financial Times – March 2016
Photographs: Tim George


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