The structural masonry of the historical monuments of the city of Belém, Brazil, is made of stones and solid bricks fixed with lime mortar, which is affected by different pathologies, including salt efflorescence and moisture action. Some authors explain that these two agents cause layer detachment, mortar pulverization, cracks and a whitened appearance. This aim of this study was to identify the degradation process affecting the masonry of the right transept of the Church of Santo Alexandre, using instrumental analytical techniques. Laboratory analyses were used in order to understand the saline efflorescence process, the material damage it causes and the main kinds of salts. The first step in the study was to map out the masonry and the damage, showing the current situation and the most damaged areas. That was followed by a physical characterisation through an analysis of mortar particle sizes and proportions, analysis of masonry moisture contents, chemical characterisation -qualitative and quantitative chemical analysis of soluble salts, and mineralogical characterisation by X-ray diffraction. The techniques applied were effective and contributed to the achievement of a correct diagnosis, guiding the type of interventions required to solve the problem.
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