Digital image analysis and EDX SEM as combined techniques to evaluate salt damp on walls

•Digital image processing of EDX analysis allow knowing the composition of the salts inside and over the walls.•The arithmetic combinations of the logical images allow establishing the spatial distribution of the efflorescences.•The methodology developed is very useful to carry out an in-depth study of the stratification of saline minerals on walls.

This work aims to use digital image analysis to characterize the superficial and in-depth regions layout/distribution of the saline phases, corresponding to efflorescences and sub-efflorescences. The possible existent saline compounds are mapped using EDX chemical element́s maps by means of logical image operations. The element́s maps are both made parallel or perpendicularly to the surface of the stonés deposit. The latter are of particular interest since they help to establish the compositional saline depth profile.The efflorescence samples were taken from the limestone siding of the Falla Chapel, in the Cathedral of Cadiz, which presents serious problems as a result of the salt crystallisation on walls.In order to validate the results obtained with the proposed digital image analysis method, a mineralogical analysis was carried out using DRX. The results produced by the digital processing techniques applied to these images generally agree with the mineralogical identification obtained by DRX. It is important to point out that the methodology developed in this research is considered to be suitable to carry out in-depth more detailed local studies of the possible stratification of saline compounds on walls, unlike other traditional analytical techniques with which only global compositional variations are obtained.