In February 2007 movement occurred in some stone steps of the main Heritage Staircase at the Queens Hotel Cheltenham and specialist contractors Ivor Parnham Building Services with Structural Engineers Glasspool & Thaiss, were requested to undertake urgent inspections.
A support scaffold was installed which enabled the hotel operations to continue and investigations to be conducted safely. The hotel staircase was built in c.1820 in an open atrim approx. 8.0m square over 3 story's from ground floor and basement. Each staircase flight and corner landing is constructed of stone cantilever step units built into the brick enclosure walls.
The landings at each floor level are of timber joists and boarding to provide access to corridors leading to various rooms. The open aspect of the stairs and atrim is capped by a decorative glass roof and decorations are generally Victorian to form an important hotel feature which is subject to strict conservation control.
The investigations were conducted by the removal of carpet and small pieces of plaster, revealing cracks in the stone steps and extensive previous mortar repairs to the tread top of the stairs and corner landings. Repair mortar was also removed in sample steps to reveal that the stonework was a relatively soft oolitic limestone which had been cut back, probably due to extensive wear from foot traffic, and reformed in sand/cement mortar.
The cracking had formed at the face of the repair, passing through the remaining stonework. Gaps were also found where the stone steps connected to the timber floor landings with evidence of poor original workmanship and strinkage in the timber landing construction.
The stability of this type of staircase is achieved by a combination of each step built into the enclosing walls providing a cantilever effect together with essential longitudinal support from the adjoining step units to transfer shared loads to the landing of each flight. In this case failure had occurred due to the loss of cantilever strength by the old cutting repairs, in conjunction with a loss if longitudinal support by the timber landing gaps.
A repair scheme was developed to remove the old mortar and reform the original step profile in a compatible reinforced adhesive mortar, including stainless steel pins at the cracked interface. The scheme included reforming joints between stone units and strengthening the timber floor landings where longitudinal support was required. Each step and landing unit was carefully checked for cracks using ultrasound equipment including the sockets for the decorative cast iron balustrade.
The repair preparation included the manufacture of samples of similar oolitic limestone steps with applied repairs of various types of materials which were tested by Building Research Establishment (BRE) to evaluate the best for use on site. In September 2007 the scope of repairs were approved and site work commenced in a phased sequence to ensure minimum hotel disturbance.
The works required extreme care and skill by the site team of Ivor Parnham Building Service working in close co-operation with the hotel staff. After completion of the first flight and landing, BRE conducted a series of on-site load tests to establish expected behavior. A total load of 5.5 tonnes was applied to a flight span of 8.0 metres overall inducing a max deflection of only 1.3mm with no cracking or movement. The repair process was then continued on all flights and successfully completed in March 2008 including refurbishment of the ornamental handrails on each side.