Front elevation at Alexander Scott's Hospital.

Deterioration seen in sandstone parapet.

Rebuilt parapet with new sections of dressed stone integrated.

Overloaded masonry with poor quality and defective mortar repairs.

Newly built in carved tracery with tooled finish.

Example of deteriorated carved sandstone flower in the string course.

LTM mason carving replacement stone for string course.

Newly carved sandstone flower cut by LTM masons.

Comparison between replacement and existing carved masonry finials and string courses.

One of the crockets decorating the finial.

Partial indent to finial.

Example of lime mortar repointing with open textured finish to squared granite coursed masonry.

Alexander Scott’s Hospital

Alexander Scott’s Hospital was built circa 1850 it is a category ‘A’ listed building located in the town centre of Huntly, Aberdeenshire.

Scope of works

Works included, decorative stone carving, replacement stone, stone indenting, reconstruction of parapet and traditional lime mortar repointing and mortar repairs.

LTM were selected to act as principal contractors for the repairs to the tower, with the works including: 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.

Technical and philosophical solutions

Prior to the practical works commencing LTM undertook a comprehensive survey of the building to ascertain the degree of deterioration to the structure as a whole and more specifically the masonry. This process had another equally important role, namely, to meticulously document and record the historic building fabric. The survey enabled the development of a sound and defensible repair strategy to be created and guide the way in which LTM undertook the project.

LTM always undertake projects with sound building conservation philosophy guiding our repair strategies, and one of the most important concepts is minimum intervention. Building conservation is an unusual field in which ‘less can be more’, or in other words meaning that the more of the original building that we leave intact the better the conservation. Unfortunately, the original stone type used for the construction of the tower was a poor quality clay-bound sandstone, a material that can be very susceptible to deterioration. The degree of decay seen left questions about the structural integrity of the parapet and selected sections of the window tracery. For this reason it was considered necessary to replace those sections of stone that may ultimately cause structural failure.

Adding to the complexity of the project the tower had moved over the years and the load paths that would normally be directed through the 4 main corners of the building had been slightly redirected. This led to the transfer of the compressive forces through the non-load bearing window panels. For this reason failure of certain sections of the window tracery masonry had occurred due to excessive over-loading.

Working in-conjuction with the structural Engineer and the Architect a suitable design solution developed and structural stainless steel reinforcing was integrated into the tower to un-load the window arrangement. The fixings for the structural intervention were hidden within the shadow lines of the tower as all parties were concerned about the impact of the repairs upon the aesthetics of the building.

In addition to structural stone work in the tracery many decorative carved stones needed to be replaced, or partially replaced. LTM masons carved new pieces of stone to replace the delaminating and deteriorating sections of stone. The original designs of the stones to be replaced were clearly evident on identical pieces located in different areas of the tower and therefore no issues of conjectural restoration were of issue.

Badly delaminated carved sandstone finial and replacement carved sandstone finial.

With the development of a repair strategy it was decided that alternative repairs to replacement stones were to be used and these included lime based mortar repairs. The mortar repairs were used to consolidate decorative masonry carving and were undertaken with pigmented hydraulic lime mortars. In areas with minimal stone delamination and contour scaling alternative repair methods were implemented. These included the use of lime based mortar repairs using nylon and stainless steel armatures, lime based mortar flaunches and the use of lime based grouts act as consolidants. It must be emphasised that the selection of a specific repair must be undertaken with a great deal of thought and may questions must be posed, including;

• Is it possible to save / retain the maximum amount of the historic fabric .
• What will be the effect upon the aesthetics of the element, component and structure as a whole.
• Does the repair offer best value, considering the longevity of the repair and life cycle costing implications.
• Is the repair compatible with the host masonry etc.

Materials used

LTM understand that when a new stone is selected for integration into an existing building that it is very important to choose a material that not only has similar colour and texture to the original but that it is also suitable in terms of its physical and chemical composition. These characteristics are equally, if not more so important as a poorly matched stone for replacement may lead to accelerated stone decay of the existing materials. LTM therefore worked directly with the British Geological Survey and commissioned analysis work to direct the most suitable type of replacement stone.

Sub-contractor co-ordination

Northern Fabricators Ltd & Jennifer Jane Stained Glass.

Logistical and site considerations

Alexander Scott’s Hospital is a working nursing home and therefore issues such as access / egress and noise abatement are at the forefront.

It was also necessary to co-ordinate the crane operations required to undertake the down taking and rebuilding operations.

Project

Alexander Scott’s Hospital, Huntly, Aberdeenshire.

Client

Alexander Scott’s Hospital Trust.

Architect

LDN Architects.

Consultant

Elliot and Company Consulting Engineers.

Solutions

Decorative stone carving, replacement stone, stone indenting, reconstruction of parapet and traditional lime mortar repointing and mortar repairs.