InfraRed Thermography, IRT, is one of the most recent techniques to monitor heritage elements, finding existing pathologies in order to implement the required maintenance tasks. However, most IRT results on cultural heritage are interpreted subjectively. Then, this work presents a methodology for the automatic detection and delimitation of moisture inside a heritage element, a mosaic in this case, from a thermographic sequence, based on the analysis of the temperature distribution of the thermal images acquired. Comparing the experimental test results with typical thermographic algorithms, the detection performance of the algorithm proposed was similar, but the new method is able to delimit and automate the whole process.