Blaenavon Ironworks began production in 1789 with 3 furnaces. Two more furnaces were built c1810. The original partnership, led by the Hill family, sold the works in 1836 to the Blaenavon Iron and Coal Co. Initial investment at the site included the construction of a water balance lift for conveyance of pig iron from the site, but further investment did not occur until the 1850s. A new blast engine was built, and a new furnace was blown in during 1861. Investment was also made on a new site kown as Forgeside. By 1900 only one furnace remained in blast, but this was blown out in 1904. Thereafter the site was used by small-scale engineering companies until it became a guardianship monument in 1974.

The cast house was built in 1788-9 contemporary with Furnace 2, one of the original blast furnaces.

Single-storey cast house of rubble stone with corrugated iron roof. The gable end front has 3 round-headed openings, of which the central is wider and higher, with tooled dressings and impost band. The gable is given simple pediment treatment with central round-headed opening flanked by bullseyes. In the R side wall is a round-headed doorway to the L, a brick arch, and a narower segmental-headed doorway to the R end. Above are 2 openings beneath the aves. The ground level is higher on this side of the building where a cast house has been demolished. Inside is a roof of light iron trusses. In the rear gable end a wide round-headed arch composed of arge white bricks opens to the furnace.

R Hayman, Hayman & Horton, 6/1/2003