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The Infrared Thermography (IRT) technique has been widely developed during the last years. IRT is useful to observe changes in the fields of physics and chemistry, and has turned out to be an important and indispensable non-destructive technique used for investigation of civil engineering works, with special attention to cultural heritage. In this research IRT has been used to study the crystallization of NaCl solution droplets with different initial concentrations (3.5, 14 and 26% weight). The crystallization was induced by evaporation of the solvent (water). Tests were carried out at two temperatures (25 and 50°C). We explained how the crystallization process is observed with IRT. The variations in emissivity recorded by the IRT described distinctly the different stages of salt crystallization. IRT allowed observing three phases. In phase I the mass diffusion within the droplet and differences in concentration and volume of the solution around the crystal germs nuclei were observed. Phase II is related to the final crystallization step, with the crystal growth and the complete evaporation of the solution. Phase III describes creeping associated with efflorescence formation. This phenomenon takes place as an intermittent decrease in the IR thermosignal which can be repeated up to 100 times in a 10 minutes interval. Different morphologies corresponded to different IRT phases. Thus, if only phases I-II are present, crystals have cubic shape or efflorescence-like with fan-shape. If phase III occurs, efflorescence-like crystals with spherulite shape develop. These spherulites can crystallize on the substrate or on previous crystals, growing by top-supplied creeping and showing an intermittent decrease of thermosignal. The study and comprehension of salt droplets crystallization by IRT is the first step in our research. Currently, we are testing different salt types and the response of salt crystallization in porous stones. Keywords: Infrared Thermography, emissivity, creeping, NaCl, temperature

In order to assess the durability of potential restoration sandstones for the cathedral ofStrasbourg (France), a comparative study was carried out on Triassic siliceous materials, socalled Meules and Vosgien sandstones. During relative humidity variations, dilations wereperformed before and after salt contamination using two salts, sodium chloride and sodiumsulfate, as well as two degrees of contamination on quarry and exposed sandstones. Sandstonebehaviors were reversible whatever the salt type: swelling under high relative humidityconditions and shrinking during low relative humidity stages. Sodium sulfate promoted onlyslight variations of dilation whilst deformation behaviors were greatly influenced by sodiumchloride that emphasized the contribution of deliquescence/recrystallization effect. As soon asthe salt had been dissolved, a slope variation related to constant swelling during high relativehumidity periods highlighted clay-salt interaction due to osmotic swelling. Thus, the dilationmethod allows determination of salt involvement on dilation behaviors during relative humiditycycles and the discrimination of sandstones.