The stone decay of monuments in relation to atmospheric environment

In order to explain why different forms of decay are present on a building facade some samples were taken from different areas of many monuments. Macroscopic observations of the forms of decay were correlated with quantitative analytical data in order to build up a simple model which was able to explain in a general way the decay phenomena. This simplified model was tested on several Venetian monuments and the features visible on stone surfaces correspond to different degree of deterioration. The quantitative analytical data were associated with the different forms of decay, which were defined as white washing, dirt accumulation and dirt washing. The results obtained showed that the features visible on stone surfaces corresponded to different degree of deterioration and the sulphate formation is greatest in the black dendrite-shaped crusts which are generally formed at the interface between the white washing areas and the sheltered ones, which were defined as dirt washing area.