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Latitude: 53.0012 / 53°0'4"N
Longitude: -3.9186 / 3°55'6"W
OS Eastings: 271345
OS Northings: 346598
OS Grid: SH713465
Mapcode National: GBR 5Z.GW11
Mapcode Global: WH559.ST6L
Entry Name: Slate Dressing Mill
Listing Date: 1 February 1996
Last Amended: 1 February 1996
Source ID: 16888
Building Class: Industrial
Location: On the main Maenofferen level, a working underground quarry, high above Llechwedd.
Locality: Maenofferen Slate Quarry
Traditional County: Merionethshire
History: The Maenofferen quarry opened in the early C19 and was developed and expanded by J W Greaves in the 1850s. In 1882 there is a recorded output of 8,494 tonnes (8,360 tons) of slate with 238 men employed. By the 1890s this had risen to an average of 1,422 tonnes (1,400 tons) and 400 men. The huge twin slate mills on the Maenofferen level are not shown on the 1888 O.S map, though graffiti exists from 1896, thereby allowing for a fairly close dating. Originally water-powered, the mills were converted to electric power c1906; the complex is still partly in use.
Exterior: Long twin-mill building (approximately 60m) of slate block construction with double slate roof; the N range is half-hipped to the W and has a corrugated iron E gable end, while the S range is half-hipped at both ends. Continuous catslide outshuts to long sides forming a flat-roofed connecting corridor in the centre, linking the two ranges. Plain skylights along each long side to light internal bays and 3 plain tin louvres to the N range. At the gable ends and the central conjunction of the ranges rail tracks enter through sliding boarded doors, allowing for supply of quarried slate and removal of both the finished product and the waste. These tracks continue along the entire length of the building internally and emerge through similar openings at the opposite end. Locomotive shed extension to the W end of the S range with small slate chimney and entrance to the S return; various blocked openings along the long sides of the mill.
Interior: Each of the ranges is 26 bays long and all original king-post trusses are retained. The N range is currently unused, though it contains various Late C19 Greaves patent rotary dressers (developed in the 1850s and patented in 1886). In addition a B6 slate planer by Turner Bros. of Newtown survives in situ . In the S range the original overhead transmission shafting is in use operating 12 belt-driven Greaves rotary dressers as before; 13 dressing alcoves are still used (on the S side), though most of the others remain, some with slate slab partitions and all with wooden L-shaped stacking benches. In the central (13th) bay, walled off from the rest of the bays, the former wheel pit, though the wheels have long been removed.
Listed Grade II* as an exceptional survival of a largely unaltered and still used late C19 slab mill.
Group value with other listed items at this exceptionally well preserved slate quarry.
References: A .J. Richards, A Gazetteer of the Welsh Slate Industry, 1991.
J.G. Isherwood, Slate From Blaenau Ffestiniog, 1988, 43.
D. Rh. Gwyn and A. Davidson, 'Gwynedd Slate Quarries', Gwynedd Archaeological Trust Report No. 152, (forthcoming).
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