Context 154 - May 2018

34 C O N T E X T 1 5 4 : M A Y 2 0 1 8 JOHN STEWART Inspecting historic fibrous plaster ceilings The risk of collapse of fibrous plaster ceilings is being addressed by a review of current practices throughout the theatre industry. Fibrous plaster is composed of gypsum plaster reinforced with sheets of hessian and timber. Its advantages were numerous: relatively light in weight; cheap to produce; fabricated off-site; and quickly installed. Fibrous plaster ceilings were either fixed (nailed directly to the structure or on to an intermediate timber system); or suspended (secured by means of ‘wads’ of hessian and plaster, sometimes reinforced with wire, to a framework of timber battens fastened to the structure). Fibrous plaster was patented in the UK in 1856 but did not enter widespread use until the 1880s. It was employed extensively in cultural, commercial, institutional and high-status residential buildings up to the second world war. It was also used for repair work or restoration carried out in earlier buildings. Despite the ubiquitous use of fibrous plaster in such buildings over this period, there is an astonishing lack of guidance on its characteristics, inspection and repair. This is because surveys and repairs are managed by a small number of busy, specialist contractors, and perhaps because demand for guidance is low, on account of owners, facilities managers or their surveyors and architects being completely unaware of its existence within their properties. All fibrous plaster ceilings, like those of plaster and lath, may be at risk of collapse if inadequately monitored, maintained and repaired. Ceiling collapse can cause serious injury or fatality. Failure can occur in suspended ceilings through natural ageing of unreinforced wads under strain, and both suspended and fixed ceilings are vulnerable to water damage from leaky roofs or plumbing. The overall condition can also be compromised by failure of structural elements, or by mechanical installations. In 2013 the collapse of an area of fibrous plaster ceiling in the Apollo Theatre, London, injured a num- ber of people. Such incidences are extremely rare. Following this incident, building and health-and-safety professionals reviewed current practice throughout the industry, and recognised a need for improvements to survey standards and competency requirements. With representatives from the theatre sector, swift action was taken to draw up guidelines to ensure that ceilings are properly inspected and maintained. The outcome was the promulgation of Guidance Note 20:Advice toTheatre Owners and Managers Regarding Suspended Fibrous Plaster Ceilings:survey,certification,record keeping etc by theABTT (Association of British Theatre Technicians), available at Guidance-Note-20-19May2015.pdf.This was based on consultation between the ABTT, the Health and Safety The void over a fibrous plaster ceiling, showing the fibrous plaster panels fixed to the original timber structure (below), with new reinforcement wads attached to new timber (above) (Photo: Richard Ireland, © Historic England)