Salts are among the most active weathering agents acting in the degradation of cultural heritage, especially on stone and brick buildings. Most of the previous works on salt weathering studied only single salt composition despite the fact that in buildings a mixture of different salts is always present. This paper presents a methodology to estimate salt weathering from complex solution composition and meteorological data, temperature and relative humidity. The proposed method uses a thermodynamic model (ECOS-RUNSALT) to predict the variation of salt volume with changing environmental conditions. To illustrate how the developed method can be applied, two examples are presented. Firstly, the model has been applied to real measurements on a repairing mortar sample sampled from a building in the center of Paris. Secondly, the model has been applied to estimate salt damage produced by a theoretical salt composition in different locations of France. Possible applications in cultural heritage conservation are (i) the prediction of future behavior of cultural heritage building materials taking advantage of climatic models and (ii) a help to determine the optimal conditions to avoid, as much as possible, salt damage.