Professional Circle Members Attend Sept. 30 Breakfast on Rare Collyweston Slate
Collyweston slate expert David Ellis
The latest in the series of Professional Circle Breakfasts featured British slate expert David Ellis.
Mr. Ellis charmed the group of architects, contractors, and preservationists as he recounted how Collyweston slate, a material unique to the UK, is hand-crafted and used in buildings across England. He is here in the US just for a week, to consult on roof restoration at Westbury House, an early 20th-century Charles II Revival country house. The magnificent mansion’s roof is composed of Collyweston, Mr. Ellis’ specialty.
Pale golden in color, Collyweston slate is formed from limestone “logs” in a limited number of English quarries. The challenging job of a slater like David Ellis includes going into an underground quarry and removing the tons of sand which have compressed limestone deposits to allow removal of the “logs.” Next, he will douse them with cold water to create ice particles which naturally split the stone so it can be separated into slates. Unlike granite slates typical of the Northeast US, which are uniform in size and shape, the Collyweston slates are derived from the separations of the limestone, and are often a variety of sizes. Like a jigsaw puzzle, the slater must determine how the pieces can be used together to create the even bands of an overlapping slate roof.
While typical in buildings across England, the use of Collyweston in the US is unusual. The architect of Westbury House, George Crawley, was British, and is thought to have selected Collyweston in reference to the 17th-century style which inspired his design. In England, slates are expected to last up to 500 years, although residue from coal fumes has shortened that lifespan in many cities across the country. In the US however, the slates have been known to fail much more rapidly, due to climate extremes and pollution.
At Westbury House, the slate roof is in a deteriorated state and the supply of replacement slates has decreased. The material has become increasingly rare, and some in the UK have called for restrictions to its export. Caretakers at Westbury House are facing several options: from restoring the existing roof, to finding new sources of Collyweston slate, to considering the use of replacement materials.
The breakfast brought together members of the Professional Circle, representatives from Westbury House, and several local slate experts who listened to the presentation and then discussed the differences in production, installation and treatment between Collyweston slate and Northeastern granite slate.
