The Orval Abbey (Belgium) was rebuilt from 1928 to 1936 using the two original limestones of the previous Abbey and a reconstituted stone made with debris of the two natural stones mixed with cement. These three materials have different salt susceptibility, especially the reconstituted stone that is highly salt-prone. The main salt found in the walls and at the surface of walls is thenardite (Na 2 SO 4).

A previous study (Thomachot-Schneider et al. 2011) showed sulphate would come from the reconstituted stone itself. Active infrared thermo-graphy (IRT) recorded on parts of the Abbey show that thermal response of salt-weathered part of walls is different from the unweathered ones (SWBSS 2014-Gommeaux et al.). This method is commonly used in heritage to detect thermal anomaly due for example to moisture, cracks or material change. In this study, we applied it in the laboratory on samples of the three building materials used in the Orval Abbey. The aim was to understand the different behaviour of these materials and to see if there could be a relation between salt concentrations in a porous network and thermal response.