Cromford Mills, the conservation of ‘Building 17’ by Marcus Stanton - News in Conservation, Issue 40, February 2014

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Building 17. Copyright The Arkwright Society

An encapsulation and restoration project at the iconic Grade I listed ‘Building 17’, the largest mill building at Sir Richard Arkwright’s Cromford Mills in Derbyshire, has been commissioned by the Arkwright Society.
The Arkwright Society has put the mill at the centre of an exciting £50 million restoration and regeneration masterplan to transform Cromford Mills into a multi-use sustainable heritage, cultural tourism, hospitality, business and enterprise destination. Building 17 is the first and key phase of the project; the building will be carefully repaired and converted to create, on the ground floor a northern gateway for visitors to the UNESCO Derwent Valley Mills World Heritage Site.
The Gateway Centre will provide information, visitor orientation and interpretation about Cromford Mills and the 15 mile-long World Heritage Site, to help local and international visitors appreciate its importance and encourage them to visit the 16 heritage sites along the valley. The four upper floors of Building 17 will contain a cluster of managed workspace units for new and expanding creative and innovative businesses. The project has received funding from a variety of sources, including the Heritage Lottery Fund.
Aside from the mill sitting empty and in disrepair for more than 30 years and being on the English Heritage ‘at risk’ register, the Arkwright Society is facing other challenges in bringing Building 17 back into public use again.
“The mill building has presented a unique challenge for us; for decades it was used for the production of colour pigments for paints and dyes. Even though production ceased in 1979 the years of use had seriously contaminated the fabric of the building making it unfit for occupation," explained Sarah McLeod, Chief Executive, Arkwright Society. “We needed to find a specialist who could restore the building to its former glory, if not, then the mill would remain empty and continue to decay," said Sarah.
In 2011, Newark-based company Bonsers Restoration were commissioned by GF Tomlinson – the principal contractor on site - to investigate the chemical imprint, including remnants of lead and chromium VI, left on the building from the dye works.
As a Grade I listed building, Building 17, presented challenges to the restoration team before any works could even begin. Bonsers Restoration and the Arkwright Society had to complete an archaeological watching brief on Building 17, one of a number of conditions placed on the listed building consents and planning permissions for Building 17. A watching brief is required whenever there is a possibility that archaeological deposits may be disturbed or destroyed. The brief involves a period of observation and investigation by a suitably qualified archaeologist to record archaeological remains during ground works within the specified area. In the case of Building 17 the findings were limited to residual remains from previous constructions within the foundations and included dividing walls, an historic stone floor and a brick culvert showing the progression and evolution of the building.
Further conditions included the retention of as much as the historic fabric as possible and any replacements to the structure being carried out using traditional methods and materials.
With the archaeological watching brief complete, Bonsers Restoration commissioned Prof Belinda Colston (Director of the Historic and Ancient Materials Research Group) at the University of Lincoln, to survey and analyse the nature and extent of the contamination, and then working with Dr David Watt from Hutton & Rostron, Bonsers Restoration examined the effect of the contamination on the building and devised a viable solution to the contamination that would allow re-occupation of the building. The survey found that the chemicals had caused the surface breakdown of structural timbers and adjoining joists and floorboards and the stone work and historic plaster in specific areas in the building had absorbed the contamination. Given the absorption into the fabric of the building, sufficient decontamination to allow re-occupation would be unsuccessful.
Richard Hill, Director, Bonsers Restoration, had to find a viable alternative if the building was to ever be used for its new purpose: "Working with the University of Lincoln and Hutton & Rostron we examined thoroughly all the trials and the investigations and decided that the most suitable methodology for dealing with the decontamination would be encapsulation."
Operations Manager, Paul Thorneycroft, headed up the team at Bonsers Restoration and began the encapsulation by ensuring that all openings to the building were initially sealed with 1000 gauge fire retardant polythene to prevent the egress of contamination during the works and then further enhanced with sealed sections within each floor level to prevent cross contamination between “clean” and “dirty” areas as the encapsulation works proceeded. This system of encapsulation requires a primary decontamination to the building, removal of all loose surface materials, cutting back horse hair in the historic plaster and lifting all wearing surfaces to carry out rigorous and thorough Hepa vacuuming of every surface. Once completed, floors are re-layed combining intermediate layers of membrane and timber and then covered with a floating floor. The structural ceiling to the fourth floor was enhanced, insulated and covered with a breathable membrane to which will be applied a traditional lath and plaster ceiling. The inherent qualities of lime act to neutralise the contamination and seal the contamination to the face of the existing walls, allowing a traditional enhanced application of lime plasters. The final make up and methodology for the application of the lime plaster was the result of detailed trials carried out by Bonsers Restoration.
Many of the remaining structural timbers were to remain visible and would therefore require an alternative encapsulation technique, again through detailed trials; an Envirograf intumescent seal was selected, which provides both the required encapsulation and has inherent flexibility.
Throughout the encapsulation Bonsers Restoration has had to try, wherever possible, to keep as much of the original as possible (to satisfy the conditions for the works being approved by English Heritage and the local planning authority) and to ensure that the remaining materials have the integrity for further use. Fortunately, aside from the timber the chemicals have had no structural impact on the remainder of the construction materials used in the building.
All waste materials from the building were deemed contaminated and had to be disposed of through either contaminated landfill sites or incineration. To date, this has included 128 tonnes of hand-excavated material sent to landfill and 12 tonnes of contaminated waste for incineration.
The working conditions presented their own set of health and safety challenges for the team. Paul Thorneycroft explained:
“Until such time as the building is encapsulated all works carried out in Building 17 are deemed to be in a contaminated environment, both with chemicals in the building materials and subsequent airborne contamination when these materials are disturbed. All employees have had to undergo bespoke training carried out by (the company) XL Hazmat covering the hazards of working in a lead and chromium contaminated environment and subsequent decontamination procedures that must be followed on site. This has required all activities to be carried out using PPE (Personal Protective Equipment) and RPE (Respiratory Protective Equipment), limiting working hours, reducing work output and requiring decontamination of employees whenever exiting the building.” Paul continued: “This has been a unique and exciting project for Bonsers Restoration. The nature, densities and location of residual chemicals have meant that we have had to continuously modify the work plans to fulfil the requirements of the project and the obligations that go with restoring a historic listed building. It’s been a valuable experience and an absolute privilege for our team to successfully accomplish this first stage in the regeneration of Cromford Mills.”
The encapsulation project is expected to be completed in March 2014 and the opening of the Visitor Gateway and creative business cluster are planned for Autumn 2014.

To follow progress of the project, please visit the project website at:
www.arkwrightsociety.org.uk

Funding for the development of the Cromford Mills site is being provided by:
Heritage Lottery Fund, European Regional Development Fund, The Architectural Heritage Fund, Derbyshire County Council, Derby & Derbyshire Economic Partnership, Derbyshire Dales District Council, English Heritage, Pilgrim Trust, J Paul Getty Jnr Charitable Trust, The Wolfson Foundation, The Monument Trust, Sylvia Waddilove Foundation UK

Marcus Stanton is a communications consultant and project team member at Cromford Mills