Atmospheric pollution effects on hydraulic mortars

On the subject of ancient hydraulic mortars, very few studies are reported in the literature regarding the origin, composition and identification of the various degradation typologies. Therefore, little is known on the effects of atmospheric pollutants, particularly those due to the dry and wet deposition of sulphur and carbon compounds, on the hydraulic mortars used in historic monuments, and few quantitative data are available. In fact, water from rising damp and sea spray are generally considered to be the only sources of sulphates, while the effects of sulphur of atmospheric origin on these materials are almost completely ignored. In an effort to fill the gap in knowledge, samples of ancient and modern mortars were collected at Italian, Spanish and Belgian modern historic and archaeological sites. The samples were analysed in order to throw light on the effects of atmospheric sulphation. The Authors present a synthesis of the characteristics of the samples analysed, together with an assessment of the damage encountered on sample surfaces as a result of the reaction between the mortars and atmospheric pollutants.