Heritage tea-breaks: petrographic characterisation of old masonry materials from Serbia and Slovenia

Petrographic analysis of construction materials is, as we know, a powerful method of elucidating information about the composition and texture of a material, that allows us to relate properties to observed behaviour, or performance (Elsen 2005, Ingham 2012). In the study of the materiality of historic structures such information on mineral content, other components and porosity, for example, are very useful for several reasons; to establish the source area for raw materials and the fabrication technology, and to determine the bounds on the requirements for compatibility for repair materials. A further refinement of the last point is to determine the benchmark for material properties, in combination with instrumental methods of analysis such as MIP, ultrasonic velocity, uCT etc, in advance of the application of treatments such as surface consolidants, in order to gauge their effect.

This paper offers selected details of an investigation into the properties of historic construction materials from two sites that have been selected as case studies in the framework of an EU- funded research project that aims to develop effective, compatible surface treatments for use in cultural heritage (the HEROMAT project, see www.heromat.com). These surface treatments are being engineered to be consolidating, biocidal and self-cleaning, with the aim of improving the durability of large scale immovable heritage in the outdoor environment.

In advance of the application of these treatments to the case studies, representative samples of the construction materials from the case studies were taken and characterised by a range of methods, including the identification of lichen surface encrustations (Ropret et al. 2012), with Raman and Infra-red spectroscopy, in-situ XRD and NMR, XRD, MIP and uCT. As the project aims to control surface properties, hardness and liquid surface contact angle were also measured. Here, selected details of the petrographic characterisation of these materials are presented.