Rochdale Town Hall is a Grade I listed building of exceptional interest, its dramatic Gothic exterior and jewel-like interior are harmonious and together they exemplify the apex of High Victorian design. The Town Hall was designed by William Crossland, a prominent Victorian architect, and is of the highest significance in terms of its historic value as one of the finest examples of a Victorian town hall nationally. As well as being an outstanding example of the Gothic Revival, it also includes early examples of Aesthetic Movement design, then a very new movement in art. Donald Insall Associates were commissioned as lead architects for the project to undertake the careful repair and restoration of the building fabric and implement sensitive alterations to improve both physical and intellectual accessibility for all.
The Great Hall [Fig 1 top] is arguably the most important room in the Town Hall. The rich internal decoration scheme comprises walls made up of painted stencil work with Henry Holiday’s mural of 1870 depicting King John signing the Magna Carta to the east gable and the much-admired Binns organ to the west. The stained glass is by Bayne of Heaton Butler and Bayne and includes two rose windows to the gables. 16 timber hammer beams, rich with painted decoration, form the main roof structure, which are supported between the wings of intricately carved timber angels. 330 painted lath and plaster panels form the ceiling between these beams. The repair and restoration of this ceiling has proven to be one of the most noteworthy challenges of the project. Hirst Conservation were appointed at an early stage of the project as specialist conservators to both carry out stabilisation works to the panels and to clean and restore the internal painted surfaces.
Stabilisation of the Ceiling Panels
From binocular inspections and limited touch tests carried out from below at RIBA Stage 3 the ceiling panels appeared to be relatively sound and, although the team were aware that some stabilisation works would be required, it was deemed that overall, the panels seemed secure. Investigations from above at this point were not possible as the few panels at eaves level that were accessible had sadly been previously replaced with replica plywood panels due to a dry rot outbreak in 1991.
Upon commencement of works on site a temporary roof was erected over the Great Hall and scaffold staging was assembled to enable the roof slates to be removed, exposing the rear of the plaster panels for inspection. A detailed examination of each bay identified a combination of issues including cohesive failure, material fatigue and mechanical stress effecting the structural stability of the plaster. The plaster nibs were degraded, extremely powdery and, in many areas, lost. The underlying plaster was also powdery and weak although the underside supporting the painted surface remained sound. This led to serious concerns regarding the stability of the ceiling plaster, which was not expected given the sound conditions to the underside.
The specialist conservators first carried out plaster analysis, which showed a quite firm but easily crushed, fine - medium grained weakly hydraulic mortar with a mix ratio by volume of 3.3:1 aggregate: binder with a reduced silica content to the failed nibs. Following extensive trials, recommendations were made that deep consolidation of both nibs and underlying plaster was required, to improve the plaster’s material condition and its structural stability, in conjunction with mechanical suspension. Suspension of the plaster without consolidation of the friable plaster would not be possible as it would be too weak and powdery to hold any support. Extensive off-site tests on samples of failed plaster nibs suggest the use of an aqueous colloidal silica as an ideal consolidant. Subsequently on-site treatment progressed and, once dry, core samples and results of limited pull tests showed a satisfactory increase in strength.
This method of stabilisation was combined with the installation of a series of pads, suspended from above as not to add additional weight to the panels. Non-functioning laths were carefully removed, and small holes carefully drilled to allow the consolidant and plaster to penetrate the panels below. The area was cleaned, and the surface treated, then pads formed from a build-up of Quadaxial fabric, rib lath and a plaster of Paris mix were applied before being mechanically fixed by a stainless-steel tie attached to a stainless-steel band spanning across the joists [Fig 2, second image].
The conservation works were deemed to be a success and risk of panel failure had been reduced, however, there was no way of definitively proving that the works carried out could support the panels. The methods used to conserve the ceiling panels were highly innovative and had never been used before, so no test data existed with the exception of the limited trials carried out on site. Any scientifically conclusive trials would have meant testing the panels to the point of destruction which was not a viable option. As such, to fully mitigate any risk of failure, reopen the building and obtain insurance cover, the team had to alleviate the residual risk of any potential future failure.
The team explored a variety of methods to alleviate this risk in conjunction with the Conservation Officer and Historic England, such as angled supports, structural wire, and a variety of netting types. Visually a fine net of a similar colour to the panels behind was deemed most appropriate and barely visible from floor level. However, there was no test evidence to prove that such a net would be capable of taking the 70kg load of an existing plaster panel and there were too many variables to prove the integrity of the netting system through engineering calculations. The team built a test rig to fully replicate conditions on site which comprised a 1.2m x 2.1m rectangular frame of 90x45mm timbers of the same strength value assumed for non-decayed existing timbers. The rig was angled at the same pitch as the roof and a netting system identical to that which the design team intended to install was attached. A representative 70kg panel was dropped onto the rig a total of 5 times, each repetition carefully observed and recorded by the structural engineers. On every repetition the netting prevented the panel from falling and therefore the netting system was deemed suitable to be installed to alleviate any risk of potential panel failure to the public below.
Restoration of the Internal Decorative Scheme
The first step in restoration of the internal decoration scheme was to gain full access to each of the panels, which involved erection of a complicated birdcage scaffold, carefully designed so as not to overload the existing structure. The main weight of the scaffold was designed to rest over the central portion of the floor, located directly over the stone vaulting of the Exchange below as this could take more weight than the suspended floors at either end of the hall, which needed to be back propped down to basement level.
Initial trials carried out at RIBA Stage 3 from a tower scaffold had revealed up to a total of 7 layers of impervious varnish had been applied over the lifetime of the Town Hall to both the plaster panels and the timber beams. These commercially prepared varnishes, commonly applied to decorative surfaces in the mid-20th century, harden by oxidation and become progressively more insoluble and yellow as they age. Further trials were undertaken to a wider selection of panels and timbers once the scaffold had been erected to ascertain the best methodology for safe and effective removal of surface dirt and varnish to underpin the development of a sound and scalable methodology for the conservation of the ceiling decoration. Methods of investigation included a visual assessment of the ceiling in reflected, raking and ultraviolet light, localised cleaning trials, and paint sampling and analysis.
Firstly, all loose dirt was removed with dry brushes, in conjunction with a vacuum cleaner to prevent the dirt re-locating. More intransigent dirt was then removed using sponges/cloths/cotton wool and water, with the area dried thoroughly immediately after treatment. The varnish was surface treated with ammonium hydroxide solution and the upper layers of varnish were carefully scraped back by hand using a scalpel blade. Acetone: Benzyl alcohol 4:1 in a gel with appropriate dwell time was then used to remove lower levels of varnish with cotton swabs [Fig 3, third image]. Trials to remove the varnish highlighted that significant touching up had taken place over the years between varnish layers and removal of the varnish would also remove later added layers of paint. This meant that careful and selective touching up of the original panels needed to be carried out prior to the final application of a modern conservation grade varnish.
Whilst the decoration to the plaster panels was known to the team, the decorative scheme to the beams was found to be much more extensive than originally assumed, as the varnishes had darkened to such an extent that the details of the stencilling beneath were all but obscured. Paint analysis found the painted decoration on the timber to be original and trial removal of the varnish revealed intricate painted and gilded designs such as the red rose of Lancashire and budding, leafy trails, sat alongside a variety of other patterning. The team saw an opportunity to bring the beams back to their full former glory and additional funding was sought from the Council to thoroughly clean the beams and, more importantly, to recruit local people onto paid work placements to support the conservators. This approach allowed the team to reduce costs whilst providing additional training and jobs in the local area. Through existing relationships with the local college, the team were able to recruit 8 art and design students for approximately 16 weeks to work alongside the conservators. From this initial period 4 of the volunteers were recruited to continue to work with the conservators until the end of the project and 1 student was given a permanent position. [Fig 4 bottom image]
Rebecca Mills, Donald Insall Associates
Client: Rochdale Council
Project Manager: Rochdale Development Agency
Lead Consultant and Architects: Donald Insall Associates
Cost Managers: Frank Whittle Partnership
Structural Engineers: Price and Myers
MEP Engineers: Max Fordham
Exhibition Designers: Redman Design
Landscape Architects: Gillespies
Main Contractor: HH Smith
Specialist Conservator: Hirst Conservation