Non-invasive FTIR study of mortar model samples: comparison among innovative and traditional techniques

Mortars are important building materials that are produced using different raw materials for the binder and for the aggregate; the latter is usually composed of several different mineral phases, or ceramic (cocciopesto) or rocks fragments. Traditional local recipes often include a vast range of organic and inorganic additives, but unfortunately no precise descriptions of the recipes have been reported in historical sources. Knowledge of their composition could be extremely significant in terms of information on past technology and improvements in today's conservation work. In recent years, non-invasive portable instruments have been increasingly used in conservation science, particularly for the analysis of paintings, but little research focuses on historical building materials. In this study, the performance of non-invasive external reflection infrared spectroscopy (ER-FTIR) is tested on model samples, which are prepared according to past recipes collected from historical manuals, and using conservation best practices. The results are discussed and compared with traditional analytical techniques, such as bench top transmission and attenuated total reflectance (ATR) infrared spectroscopy, combined with powder X-ray diffraction (XRD). The influence of surface roughness on reflection infrared spectroscopy signals is also considered and investigated.