Roof Slates Northern Ireland | Welsh Slates, Cwt-y-Bugail

Welsh Slates, Cwt-y-Bugail

The Cwt-y-Bugail quarry in North Wales has been producing quality dark blue grey roofing slates from 1840.  Located East of Blaenau Ffestiniog in the Snowdonia National Park, it is the highest industrial site in the UK and although the site is now an open cast quarry, slates were originally mined in deep caverns and pillars.  In fact, during World War II, many of Britain’s most valuable paintings and national treasures were stored deep inside the slate caverns for safe keeping!

Referred to in Ireland as 'Portmaddog Slates' (after the port from which they were shipped)  the dark blue grey slates produced by this quarry have a “riven” texture and are famous, not only for their use as a roofing slate, but also as an architectural building material.  Although quite different in colour to the Bangor Blue slate, they share the quality and durability with which Welsh Slate is synonymous. 

Please contact us on 02877741686 or to get more technical information or pallet quantites



Cwt-y-Bugail slates come in standard sizes of 500x250mm (20 x 10”), and in 3 thicknesses:

  • Capital Grade (5.5mm Nominal Thickness)
  • County Grade (7.5mm Nominal Thickness)
  • Celtic Grade (9.5mm Nominal Thickness)

Cwt-y-Bugail roofing slates conform to BS 12326-1:2014 (W1, S1, T1), hold BS Kitemark accreditation and are generally expected to outlive the life of a building (when fixed in accordance with BS 5534 / S.R. 82:2017).


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