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• Experimental tests were carried out for the evaluation of water repellents for masonry. • Infrared thermography was used to monitor the wetting and drying of laboratory walls. • Wetting and drying test were also carried out on treated/untreated bricks samples. • Multitemporal IRT images were processed by Change Detection Analysis (CDA) • Interesting data were obtained on water repellents' effectiveness and compatibility. Moisture is one of the main problems that affect new and historic masonry buildings, which are the most common ones in Europe and worldwide. The application of surface treatments based on water-repellents is a very common solution to protect masonry from rain and hence from moisture-related problems. However, there are very few studies on the monitoring of water-repellents in real buildings and a deeper knowledge would be necessary on the long-term effectiveness and compatibility of water repellents, especially considering that defects and flaking issues are often reported in-the-field. In this paper, infrared thermography was proposed as a totally non-invasive technique to monitor the behaviour of brick masonry subjected to wetting, both from outside (rain) and inside (internal moisture). An active thermal approach was used to simulate internal and external wetting. The behaviour of the masonry during wetting and drying was investigated both in laboratory walls and in brick samples, to elucidate their water transport properties. All the materials were tested both in untreated conditions and after the application of two different hydrophobic coatings. The results show that the drying behaviour of treated masonry materials is a critical issue, as the coatings may strongly slow down the drying of internal moisture, even if the coefficient of resistance to water vapour diffusion of the products is very low. The results also suggest that the methodology used to process thermal images using multi-temporal analysis is a promising way to interpret the water transport in treated walls and to monitor real buildings where water-repellents were applied. [ABSTRACT FROM AUTHOR]