Built in 1900 by leading brewery architects George Adlam & Sons of Bristol, for Charles Westlake. At time of its opening it was acclaimed by the Brewers Journal as 'of the most substantial character in every way' and 'the plant will be of the most modern description, both scientifically and practically.' This new brewery superseded the one opened by Charles Francis Westlake in Blaenavon in the 1880s; unreliable water supply led to the move down to Cwmavon. The company, Westlake's Brewery Ltd, had been founded in 1889. By 1907 the company had a chain of pubs and in 1911 Westlake's took over the Castle Brewery in Pontypool. The business declined in 1920s and brewing at Cwmavon ceased in 1928. In 1936 the buildings were taken over by The Eastern Valley Subsistence Production Society with the objective of helping the problem of local mass unemployment. Now the former brewery has been converted to a plastics factory.

The S block comprises 2-storey gabled N and S ranges and 1-storey range at right angles between. Rock-faced stone with brick dressings, and asbestos-cement roof. The N end range is higher. Its W gable end, facing the yard, has inserted lower-storey openings and blocked segmental-headed openings in the upper storey. Its N side wall has 6 lunettes in the upper storey. The single-storey range is 6 bays long and heightened in brick. Round-headed openings include a single doorway and a doorway cut in R of centre. The S gabled range has, in the lower storey a round-headed window with small-pane glazing and blocked first-floor doorway. The S side wall has 6 upper-storey lunettes, 4 with small-pane glazing and 2 blocked, and inserted doorway in the lower storey.

R Hayman, Hayman & Horton, 20/1/2003