General view of washery, Maerdy Colliery, 1975. Photograph by John Cornwell.

In 1947 the coal industry was nationalised; two years later the National Coal Board announced the complete rebuilding of Maerdy Collieries No.3 and No.4 Pits, near the head of Cwm Rhondda-fach. The mine had closed in 1940 and was lying derelict.

The rebuilding swept away most traces of the original structures but provided an all-electric state-of-the-art colliery with new winder houses, coal preparation plant, administrative offices, a canteen, pithead baths and medical centre. Developments underground included new roadways to link with Bwllfa Colliery in the Cynon Valley.

The site of Maerdy Collieries Nos.1 and No.2 Pits had been retained for railway sidings in connection with Nos.3 and 4 Pits and continued in use to serve the new Colliery.

The last coal was raised at Mardy Colliery in 1986 although coal continued to be mined and brought to the surface at Tower Drift Mine, with which it was linked underground. Mardy closed in 1990 and the site has since been demolished and cleared.