Gelmast Farm was a planned 'experimental' farmstead established by Thomas Johnes of Hafod ca. 1803, intended to showcase Johnes' ideas on grassland management, stock, and dairying, and to supply milk, butter and cheese to the district, including the lead-mining area.

The two-storey farmhouse is of painted stucco with slate eaves, and comprises a three-bay main house, with a two storey, double fonted service range to the right. Projecting from the rear of this block is the dairy with hipped slate roof. Attached to the left of the house is a three-bay dutch-barn or cartshed with stone piers, corrugated roof and doors, and beyond a plain rubble stone block, possibly once a lofted stable, with slate roof and blocked door to front. To the right of the house is a long cowhouse, again in plain rubble stone block with a slate roof.

Source: Cadw Listed Building Record

K Steele, RCAHMW, 9 February 2009