The authors investigated microstructural development and selected physico-mechanical properties of the sandstones that were treated with structural strengthening chemicals. The method involved impregnation of the pore space of the rocks with various organic compounds that after polymerization at least partly cemented the grain framework. To obtain proper strengthening of renovated, damaged parts of the rock, the substance after polymerization should attain physico-mechanical properties approximating those in unaltered parts of the rock. The investigations were carried on the samples collected from selected outcrops of the Istebna sandstone ("Droginia" deposit), the Godula sandstone ("Straconka" deposit) and the Szydłowiec sandstone ("Podkowiński" quarry). The paper presents dependences between diversified lithologies of the natural sandstones and the changes of their physico-mechanical properties resulting from application of various strengthening substances. The changes resulting from impregnation in unaltered sandstone samples allow to predict efficiency of the same strengthening processes that can be applied to various types of damaged sandstones in historic buildings.