A method for quantitative mineralogical analysis by ATR-FTIR [1] has been used first timefor analysis of historical mortars. Mixtures of different minerals and gypsum were used in orderto measure the minimum band intensity that must be considered for calculations and the detectionlimit. In this way, the molar absorptivity coefficient in the Lambert–Beer law and the components ofa mixture in mol percentage can be calculated. The GAMS equation modeling environment and theNLP solver CONOPT (©ARKI Consulting and Development) were used to correlate the experimentaldata in the samples considered. The characterization of the vernacular mortars by FTIR analysisidentifies the predominant minerals of the samples, and in conjunction with XRF and XRD, showsthe exact composition of historical mortars, which will optimize the restoration and conservation ofmonuments, preserving our heritage.