Graig Ddu slate works was built in the 1880s and was initially water-powered. It was supplied with slate from the quarry further uphill by means of an inclined plane (nprn 537327). Several reservoirs, or dammed natural lakes, were used to supply water (nprn 537339, 537349, 537347, 537367, 537463, 537469, 537471), by means of existing streams, leats (nprn 537350) or iron pipes, supports for which have survived (nprn 537222, 537223, 537332). On the works site is a waterwheel pit (nprn 537341) and buildings (nprn 537334, 537336, 537338, 537342, 537344537461, 537459, 537458). In the early C20 water power was superseded by a gas-powered engine, the base of which has survived (nprn 537343). On the W (downhill) side of the works are spoil tips (nprn 537348, 537460). The works continued in production until 1946.
A.J. Richards, Gazeteer of Slate Quarrying in Wales (2006), pp 189-90.
Recorded as part of RCAHMW Uplands Initiative Project, R Hayman, H & H, 12/03/2014.