The article deals with the subject of renovation of historic buildings on the example of the 19th century Town Hall in Maciejowice in the Mazowieckie Voivodeship. Attention is drawn to the diagnosis of the technical condition of the historic building (f.e. scale and range of degradation, measurement of the level of dampness of buildings construction, testing the level of salts in walls) and the possibility of using building chemistry, including moisture regulating plasters characterized by higher vapour - permability, to protect the structure against water coming from the external environment. This is an important issue, because in the temperate climate of Poland, environmental conditions are one of the reasons for the occurrence of increased degradation processes of plaster coatings and elements of building structures. Authors of many scientific publications in Poland, but also around the world, take under consideration the influence of naturally existing water on lifetime of building and it’s elements.