Award of Repairs to the Historic Plasterwork of the Adam Dome

Tender description

The Adam Dome ceiling comprises neo-classical decorative plasterwork executed by Thomas Clayton Jnr. to Robert Adam’s design of c.1785. The domed ceiling, centred around a glazed oculus, is divided into eight segments by decorative ribs which are further compartmentalised with horizontal friezes creating plain plastered fields which are embellished with cast decoration and smaller run mouldings. The decoration within the largest compartment of each segment include large roundels consisting of plain run mouldings which frame casts of classical figures. The plaster consists of lime-based gypsum gauged plasters applied onto a background of riven (hand split) timber laths. The ceiling from above is divided by primary trusses which has created 12 segments. Each segment is divided into four sections by horizontal timbers which support ceiling joists that further sub divide each section into bays.The decorative elements applied to the ceiling comprise a mixture of run in-situ and bench run/precast mouldings, embellished with cast decoration. The condition of the ceiling from above is generally poor, caused by a combination of missing and damaged plaster nibs, water damage, defective timber laths and structural issues found in the roof space during a condition survey (report appended) carried out in 2019. As a result, a pattern of longitudinal cracking in the vicinity of the vertical ribs, which had reoccurred since the ceiling was last repaired and decorated in c.2007, was observed on the underside of the ceiling. This was further evident in cracking through plaster monitoring dabs applied in May 2019, indicating on-going movement. Movement was detected in most of the cracks in these areas when upward pressure was applied. Trial repairs were carried out in 2020 on an area of ceiling (see appended report) and form the basis of repairs which will be carried out throughout the rest of the ceiling. Much of the work will be carried out within the confined roof space above ceiling, where access platforms and ladders, and a fall arrest system have been installed. Repairs to the underside of the ceiling are accessible from a scaffolding provided by the client. The proposed plaster repairs comprise four main elements: • Screwing up from below through plain plastered areas into timber above. It is anticipated that this work will be carried out before any work is carried out in the roof space. • Plaster nib and timber lath replacement from above using a proprietary repair system. • Supporting heavier decorative elements (friezes and ribs) with wires. • Patch repairing cracks, holes and disrupted surfaces in preparation for redecoration by others.