Craig Ddu slate works (nprn 537337) was built in the 1880s at the foot of the upper incline below the quarry. It continued working until 1946. The large mill building has mostly fallen and its extent is determined only by wall footings. It measures 23m long N-S by 12m. Some walls, of quarried slate blocks, survive up to 1.9m high. Inside the building there is some turf cover and fallen debris, but a base with holding-down bolt is visible, as is a slab-lined trough 0.8m by 0.9. Along the E side is a lower linear, stone-lined pit in line with the waterwheel shaft further N.
Recorded as part of RCAHMW Uplands Initiative Project, R Hayman, H & H, 10/03/2014.