Block Mill And Numbers 35 And 36 Stores (Building Number 1/53)

Two wood mills, block mill and pump house, now disused. Built in different phases between 1799 and 1806, planned by General Sir Samuel Bentham and probably designed by architect Samuel Bunce, with James Sadler arranging the power system. The buildings were constructed above a basin dating from 1691-1698, originally built by Edward Dummer. Bentham covered this basin and inserted a storage floor within it in 1799. Red brick construction, some parts with blue headers in English bond; ashlar dressings and gauged brighter-red brick flat arches. Hipped slate roofs, with the north range roof later altered to a gabled roof, probably in the early 20th century.

The building comprises three parallel ranges. The north and south ranges are the former wood mills, each of three storeys with cellar and measuring three by eleven bays. The central block mill, built between them, is one storey with dimensions of three by thirteen bays, projecting at its east end. A walkway runs across the central block mill to link the two outer ranges at first-floor level. Windows throughout are mostly replacement small-paned pivoting windows with flat brick arches and projecting stone sills. Board doors with small-pane overlights provide access. An ashlar plinth and first-floor band run around the building, with a stepped dentilled brick eaves band and coped parapet to the south range.

On the west elevation, a central door opens to the ground floor of the south range, with four continuous doors accessing the ground floor of the north range. A central loading door serves the upper floors of the north range, positioned at second-floor level with a wooden platform and crane. The central range features a central sash window flanked by doors, all set within round-arched recesses with a continuous impost band, and a corniced pediment with a small-paned lunette above. The east elevation is similar in design. The central range has bricked-up windows in recesses, with two windows on the left return and a window and door on the right return. The north range has three round-arched doorways on the ground floor, the central one blocked, with central loading doors to the upper floors and sixteen-pane sash windows to the second floor. Two old board doors open onto the ground floor of the south range, with central loading doors on upper floors. A lamp bracket is mounted on the left corner at first-floor level on the south elevation.

Internally, wooden columns support large-scantling cross-beams. The central range has turned columns, while the north and south ranges have square and chamfered columns. A probably original stair survives in the north-east corner of the south range, featuring large scantling plain balusters. Remnants of the former power transmission equipment include overhead shafting, pulley wheels and belts. Fixed machinery survives on the first floor of the north range, including a lignum vitae saw, treenail machine and cornering machine. The frame of a circa 1800 Boulton and Watt beam engine remains at the end of the south range.

Beneath the south range, Bentham's infilled basin survives, filled with a double tier of brick vaulting. The basin continues to function as a reservoir with a storage floor above, featuring brick vaults carried by segmental-arched arcades and a stone flag floor with drains. Seventeenth-century dock walling also survives, formed of large blocks of tooled masonry, with a projection at the south-west corner, possibly the base for a sheerleg crane, and machinery for Number 1 Penstock.

The mill was purpose-built for innovative block-making machinery, designed by Marc Brunel between 1801 and 1806 and constructed by Henry Maudslay. By 1806, forty-five machines operated by ten men were producing 140,000 blocks a year for ships' rigging, with capital costs recovered within three years. Built for both dock pumping and wood working using the Navy's first steam engine, the Block Mill is of international significance as the earliest application of steam-powered machine tools for mass production.