Just behind the Pottery on Vicarage Road stands a roofless engine house (the only one of West Kitty’s three engine houses still standing) built in 1892 to house a 40″ (cylinder diameter) beam engine used to pump water out of the southern end of West Kitty Mine at Thomas’ Shaft
Why the different building materials?
Cut granite was always favoured for the cylinder bedstone, the bob wall and corners – the latter known as ‘quoins’. Gable roofs were covered with Cornish slate and bricks were brought to construct the top most section of the chimney stacks and window and arch details. Most surviving engine houses are rectangular in plan with a much thicker wall in the front (the bob wall). This was constructed using massive stones (often cut granite) and was perhaps two-thirds of the height of the other walls. It supported the beam (known in Cornish mining as a bob), which transmitted the reciprocating motion of the piston to the pump rods in the adjacent shaft (in the case of a pumping engine) or to the hoisting or crushing machinery. This wall had to withstand both the weight (that might be over 50 tons for a large pumping engine) and the rocking forces of the bob.
source: Cornish Mining