Scope of Work

Pictured: Alexander Scott’s Hospital: during works.

LTM were contracted by the Hospital Trust as principal contractors for the repairs to the square porte-cochere tower over a 5 year programme. The works included: introducing internal structural steel work and stainless steel reinforcing bars into the tower; down-taking, repairing and rebuilding the masonry parapet including replacement and indenting sandstone and decorative sandstone carving; selective lime based mortar repairs to all elevations and isolated repointing to coursed granite masonry and sandstone ashlar masonry dressings.

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Challenges and Considerations

Pictured: Tower parapet: masonry condition.

Alexander Scott’s Hospital is a working nursing home: understanding the site was therefore crucial to a safe and efficient working environment. The key issues were: negotiating site access/egress, minimising noise pollution and co-ordinating the crane operations.

The primary challenge however was the structural movement of the tower itself. Over the years the tower had moved, thereby redirecting the load paths that would normally be deflected through the four main corners of the building. This, in turn, led to the transfer of compressive forces through the non-load bearing window panels, resulting in excessive over-loading and localised failure of the window tracery masonry.

A suitable design solution was developed in conjunction with the structural Engineer and the Architect. Structural stainless steel reinforcing was integrated into the tower to strengthen the tower and minimise the deflective thrust onto the tracery window. The fixings for the structural intervention were hidden within the shadow lines of the tower in order to reduce the impact on the character and appearance of this Category ‘A’ Listed building.

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Solutions to Problems

Pictured: Replacement finial.

The original building stone is a poor quality clay-bound sandstone, a material that can be susceptible to physical deterioration due to its mineralogical composition. The degree of decay raised concerns regarding the structural integrity of the parapet and selected sections of the window tracery.

LTM undertook a comprehensive building survey to ascertain the degree of deterioration to the structural fabric, focusing on the mass masonry blocks. Importantly, this process included the meticulous documentation and recording of the masonry in terms of location and condition. The survey provided a sound conservation and repair strategy for stone replacement and repair.

Replacement stone: when replacing stonework it is critical that new stone matches the existing in terms of its physical and chemical composition as well as colour and texture. Poorly matched replacement stone can exacerbate the decay process and ultimately negate works to conserve the physical fabric. LTM therefore worked closely with the British Geological Survey and commissioned laboratory analysis to inform the specification. LTM masons also recorded the decorative stones suffering from surface delamination in order to replicate the original design on replacement carved stones.

Mortar repair: delaminating decorative masonry carving was repaired and consolidated with a pigmented hydraulic lime mortar. Alternative repair methods were implemented in areas with minimal stone delamination and contour scaling, including the use of lime based mortar repairs with nylon and stainless steel armatures, lime based mortar flaunches and the use of lime based grouts to act as a masonry consolidant.

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