Backbarrow Pug Mill, Cumbria. Archaeological Assessment, Fabric and Turbine Survey Report.

An archaeological survey was undertaken of the Backbarrow Pug Mill, Haverthwaite, Cumbria (SD 3555 8470) in advance of a proposed commercial development of the site. A feature of this development was the conversion of the former Pug Mill for use as office accommodation. The work entailed the production of a documentary study specifically targeted on the Pug Mill, a fabric survey which enhanced existing architects drawings, and an assessment of the turbines on the site. The work was undertaken in December 2002, and an interim report was submitted in the same month. The present report is the final statement of the investigation results.

The Pug Mill is at the northern end of the Backbarrow iron working complex, which has been producing iron since 1685. The main episode of the iron manufacture, however, was from 1711 when a blast furnace was constructed on the site. Since then, the site has undergone many changes and developments, including the rebuilding of the blast furnace in 1870. In the 1920s the blast furnace was the last in the region to be converted from charcoal burning to coal burning. The works continued in operation until 1964 when it was closed.

The Pug Mill was an important development, located so as to exploit the River Leven water source, it would appear to correspond with the location of the original bloomery forge built by John Machell in 1695. With the construction of the blast furnace in 1711, a finery forge was established on the site, probably adapted from the original bloomery forge. In 1866 the Pug Mill was adapted to accommodate a 8.5hp water turbine in the place of a water wheel, and then a further turbine (of 40hp) was added in 1869. In 1920 two further turbines were installed to provide electrical power for the site, one of 12hp and one of 49hp, and a further installation was made in 1927 of a Gilkes, generating 120hp. This outlasted the iron production and continued to provide electrical power for the National Grid until it was eventually closed in 1999, prompted by the construction of an adjacent new hydro-electric installation.

The fabric survey identified five extant phases of construction. The original phase was the possibly the original bloom smithy, and the western wall of the western ground floor room is the only extant element of this. This incorporates a mounting block, possibly for an axle, suggesting that there was a former water wheel set into a pit on the western side of this wall. The second phase of construction was the addition of a water wheel housing on the eastern side of the building, where the axle mounts for a water wheel survive. The third phase appears to relate to a change of function of the mill from forge to power house, with the insertion of a succession of water-powered turbines. This entailed the construction of an eastern extension presently occupied by the turbines and power generation equipment. The fourth phase of construction comprises the expansion of the structure to the west and appears to relate to the insertion of a forge into the upper floor of the Pug Mill. The final phase of activity related to the Pug Mill’s continued use for power generation through the twentieth century and entailed the expansion of the power facility to accommodate the installation of the large Gilkes turbine in 1927.

The turbine assessment identified the existence of two surviving turbines, the large 1927 120hp turbine within a central penstock pit, and a smaller turbine in the Phase 2 wheel pit. The latter was identified as the 12hp Gordon turbine of 1920. The large 1927 turbine was unusual in that it had a propeller runner, and was the only turbine made by Gilkes to this general specification.

It is recommended that the development and conversion should be allowed to proceed as this will ensure that the building is preserved and will prevent its natural decay; however, the conversion of the building should involve as little intrusive disturbance to the existing fabric as possible. Given the unique character of the large Gilkes turbine it is recommended that this should be preserved in situ, and if possible also the mechanical components of power generation.

It is recommended that an instrument survey be undertaken to accurately locate the phasing relationships on the south external elevation and to produce an accurate plan of the features located within the former wheel pit. It is also recommended that detailed elevations be produced of the internal elevations of the western cell of the ground floor (GF1). Any external ground work should also be undertaken under archaeological supervision as it is likely that remains of water courses and possibly earlier structures lay close to the Pug Mill.