Worcester Park Gunpowder Mills and John Smeaton, ‘the father of civil engineering’

Worcester Park Gunpowder mills
Worcester Park Gunpowder mills

In 2020, during the covid pandemic, CA Andover carried out an excavation at a former industrial site at Worcester Park, Surrey, prior to redevelopment. Trial trench evaluation in 2019 had already identified some surviving structural remains, correlating to the former Worcester Park Gunpowder Mills (c.1720-1854) on early 19th-century maps, and the extent of these remains quickly became clear to the team once the expanses of concrete slab that lay across the site were removed.

Working on former industrial sites can be incredibly challenging and full of risk, but updated daily assessment of Safe Systems of Work, along with additional specialist support such as UXO (unexploded ordnance) monitoring, enabled full and safe excavation and recording of the comprehensive, well-preserved remains of the brick-built mills and their ancillary structures.

A bird’s-eye view of the remains of the two powder mills, and the culverts that provided and drained the water needed to power them
A bird’s-eye view of the remains of the two powder mills, and the culverts that provided and drained the water needed to power them (© Aerial-Cam)

The remains of two powder mills were identified, both with barrel-vaults, blast walls, buttressing and foundations up to 4.5m deep below the concrete slab, all encased in redeposited clay that resembled a type of protected military bunker. An extensive and elaborate water management system and former canal were also revealed, and it became apparent that the structural evidence as excavated was directly comparable to the detailed 18th-century powder mill designs hand-drawn by their architect, John Smeaton, which are held by The Royal Society. The system of culverts supplied a controlled flow of water from the nearby Hogsmill River that powered the waterwheels and drove two pairs of large millstones to grind together the gunpowder ingredients within each powder mill.

One of the wheel pits (full of water) with scarring from the waterwheel visible on its facing wall. The barrel vault to the rear housed the gear mechanism that turned the millstones above; to the left are the upper and lower culverts that brought and drained (respectively) the water to power the wheel
One of the wheel pits (full of water) with scarring from the waterwheel visible on its facing wall. The barrel vault to the rear housed the gear mechanism that turned the millstones above; to the left are the upper and lower culverts that brought and drained (respectively) the water to power the wheel

Waterwheel scarring was apparent on the face of one of the wheel pit walls. The diameter of the scarring indicated a waterwheel diameter of 9ft, identical to Smeaton’s illustrated design. This is believed to be the only time John Smeaton employed this size of waterwheel. Wheel scarring was also identified within one of the barrel-vaults, from the turning motion of the gear mechanism. The brick foundations of associated outbuildings were also recorded, one of which corresponded to a steam drying house, also represented on John Smeaton’s designs. Other remains included in situ timber decking, structural timbers, a silt trap, and timber flooring and ceramic tiled paving within the culverts. Finds included a cluster of preserved timber teeth from wooden cogs, small timber wedges, metals, leather, textiles, ceramic artefacts and charcoal deposits of industrial waste.

A 3d model of one of the gunpowder mills

The broken millstone
The broken millstone

Our investigations showed just how dangerous gunpowder production could be. The massive nature of the brick-built vaults, blast walls and buttresses was designed to channel any blast upwards rather than outwards, in the event of an explosion. Historical records tell us that this occurred seven times during the working life of the powder mills at Worcester Park, killing four and injuring an unknown number, including two explosions that led the closure of the mills in 1854. Evidence for explosions, and subsequent repairs, was found on the surviving remains, including an enormous millstone within one of the barrel-vaults that had been broken in two, as well as scattered explosion debris of smaller shattered millstone, brick and timber fragments. 

The site was incredibly rewarding and far exceeded anyone’s initial expectations of what could be found. The remarkably well-preserved remains brought to life the work of the ‘father of civil engineering’, John Smeaton, from the period of intrepid engineering innovation that was the industrial revolution.

Matt Nichol

Further details of our excavations at Worcester Park Gunpowder Mills are presented by Matt in an illustrated talk on our YouTube channel.

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