A holistic approach to evaluating the performance of consolidants on sandstone
Keywords: Sandstone
Heritage Science
Heritage
Consolidant

Sandstone, one of the most ubiquitous building materials around the globe and across time presents a complex range of characteristics and responses to environmental and physical erosion over time. The range of sandstone sub-types that have been used for structure and decorative carving through history was highly variable but is diminishing as a resource as more and more quarry sites are worked out or closed. This process has led to the use of ‘replacement’ stones in conservation work which are sourced from a small number of known sites and are similar to historic types in appearance if not age or internal characteristics. This project examines one of these replacement stones, Locharbriggs sandstone from Dumfries in Scotland, and couples it with two of the most commonly used silane consolidants in order to improve the understanding of the performance of both in lab and field conditions.
The project begins by taking observations on site at Kenilworth Castle (Warwickshire, UK) shaping the research through the identification of areas of concern for the conservation of historic sites, such as erosion driven by visitor footfall and the effects of prior treatment applications. These are used to formulate an experimental programme which combines lab and field experiments, and begins with the development of a method for artificially weathering the stone substrate using the controlled application of heat, in preparation for consolidation.
The field-based experimental work, hosted at the Wytham Woods research site near Oxford UK, examines the uses and limitations of two forms of field trial; the exposure of laboratory-prepared stone samples on a purpose-built exposure rack, and the incorporation of stone samples of variable size and treatment within a purpose-built test structure. Both experiments trial a range of assessment metrics for the detection and monitoring of consolidants applied to the samples, within the context of exposure to local weather conditions. In addition to these experiments, a further trial was hosted by SATRA Technologies (Kettering, UK) which utilises a mechanical prosthetic leg to simulate physical abrasion analogous to that observed on site, modelling the type of wear driven by footfall across exposed stone surfaces.
These experiments trial the use of a range of systems for the assessment of stone condition and consolidant performance, combining those which are understood in other heritage contexts with the novel combination of handheld optical and laser scanners for the detection of change on samples. These are formalised into a ‘toolkit’ of methods and instruments that can be applied to sandstone- consolidant experiments, including novel methods of visualising and analysing data.
The thesis concludes that the range of assessment techniques trialled here have a range of useful applications in the detection of consolidants in heritage sandstone and for the detection of change on site and in laboratory conditions, and that there is significant scope to employ them in a range of conservation applications.