Sandstone weathering in urban environment observed on the walls from Warsaw metro entrances

The paper discusses the problem of sandstone deterioration on walls in entrances to the Warsaw metro. The Brenna sandstone that builds these walls is a feldspatic greywacke, commonly used as a building stone in Poland. The author has found several weathering forms on the stones - a dark-colored crust tracing the surface, scaling, back weathering due to loss of crusts, clearing out of stone components, encrustations, efflorescences and subflorescences. Geological researches using optical microscope, scanning electron microscope and x-ray diffraction show the nature of deterioration products. Different carbonate and sulphate salts were found in weathering forms generatedfrom water solution that migrates through the sandstone. Atmospheric deposits, observed on the surface of sandstone blocks, contain mainly soot and silicates