Evaluation of evaporation flux in building materials by infrared thermography

The presence of water inside the walls can be considered one of the most important causes of degradation in historical buildings. This is particularly due to evaporation which can give rise to salt deposits inside the superficial pores. Evaporation flux from wall surfaces can be estimated quantitatively by measuring the temperature which depends in a sensitive way on the evaporation rate. At equilibrium condition among all the different kind of heat exchange the wall temperature depends essentially on the evaporation rate and the thermal properties of the material (porosity, conductivity). In the Archaeometry lab of “Istituto di Fisica Generale Applicata” we performed some experiments on several brick, plaster and stone specimens with different porosity in order to obtain different evaporation rates. We employed a climatic room where environmental parameters (temperature, RH, ventilation and irradiation) are controlled and cooling effects due to evaporation are investigated by a SW IR thermographic system in steady conditions in order to understand the relation between evaporation flux (), water content (Wc) and surface temperature (Ts). Table of comparative values of these three variables (, Wc, Ts ) were obtained for several materials and applicability limits of the thermographic technique for moisture detection are discussed