LAUSR

Abstract Degradation of historical masonry and plasters is often caused by external conditions; the presented research focused on salts originating from subsoils. The content of salts: Sulphates, Nitrates and Chlorides was analysed from plasters on 5 chosen historic buildings before and after the renovation in this paper. The samples were collected three times between 1998−2018. In some cases, the Sulphates were still present or even with a higher content after the renovation in comparison with the state before renovation. That can be caused by many factors from environment and this work focused on source from the subsoil. To understand better geological background the borehole data around each object were studied. According boreholes were buildings divided in two groups: on clayey subsoil and building on subsoil without clay. By Kruskal–Wallis test was proved, that the Sulphates content in plasters was constant before and after the renovation on clayey subsoils, it didn´t changed in a time. On subsoils without clay (mainly silty to sandy soils) the content of Sulphates declined after the renovation, what was proved by regression analyse on 95% confidence level.