Welsh Slate

Welsh slate is natural roofing slate from the quarries of Gwynedd in north-west Wales, especially around Bethesda, Llanberis, Nantlle and Blaenau Ffestiniog. For about 150 years it was the dominant roofing slate in the world, and it is still produced today.

History

Slate has been worked in north Wales for nearly two thousand years: the Roman fort of Segontium at Caernarfon was roofed with local slate in the late second century. Large-scale commercial quarrying began in 1782 at what became Penrhyn Quarry near Bethesda. By 1882 Wales produced 92% of Britain's slate, about 451,000 tonnes, with Penrhyn and Dinorwic together accounting for half. According to UNESCO, by the late 19th century the region produced about a third of the world's roofing slates and architectural slabs. Skilled Welsh quarrymen emigrated to start or expand slate industries in the United States, continental Europe and Ireland.

Labour relations were difficult. The Great Strike at Penrhyn, which began on 22 November 1900 and lasted three years, is often described as the longest dispute in British industrial history. The last large underground working, Maenofferen, closed in 1999.

Penrhyn Quarry

At the end of the 19th century Penrhyn was the largest slate quarry in the world. Its main pit is nearly 1 mile (1.6 km) long and about 1,200 ft (370 m) deep. Nearly 3,000 men worked there at its peak; the workforce is now nearer 200. Larger quarries now exist in Spain, China and the United States, but Penrhyn remains the largest in Britain.

Heritage status

The Slate Landscape of Northwest Wales was inscribed on the UNESCO World Heritage List on 28 July 2021. It is a serial site of six components that includes quarries, mines, settlements, railways and the export harbours of Port Penrhyn and Porthmadog. Welsh slate was also designated a Global Heritage Stone Resource by the International Union of Geological Sciences in 2019.

Properties

Welsh slate is typically blue-grey, purple or heather-toned. EN 12326 test results published by a supplier for Penrhyn slate report very low water absorption (0.14%, class A1), low carbonate content and the T1 and S1 classifications.