The durability of building stones is controlled mostly by the following properties: mineral composition, texture, pore area parameters, and pore fluid phase composition and its content. Stone elements in building objects might be regarded as open hydrochemical systems, whose initial chemistry is set at deposition stage. Chemistry of the system changes when infiltrating water moves chemical components through pores, and causes either leaching or cementation of grains. The weathering processes could be clearly presented by hydrogeochemical modeling (reactive transport models). The paper presents an example of hydrochemical modeling of weathering processes within the clastic rock, used as a building material. The examined rock is Cretaceous quader sandstone from Radków deposit (intrasudetic basin, Lower Silesia, Poland), widely used in architectural monuments in Central Europe. The rock is quartz sandstone of high porosity of over 20%. Dominating pores are macropores (84%). The modeling was conducted with use of geochemical simulator The Geochemist's Workbench 7, estimated the influence of destroying environmental factor (atmospheric water of urbanized area) for rock. In the model the total pore area is assumed to be saturated by rain water, hence the reactions are related to the external part of a building rock. The time of saturation and evaporation stage is established for a one day (24 hours). Themodeling estimated the influence of destroying environmental factors, i.e. atmospheric water of urbanized area. Model of rock-water interactions showed that the porosity increase is connected to decomposition of carbonate minerals (calcite and dolomite). Decomposition of other minerals (aluminosilicates) starts during the evaporation cycle, but the scale of the phenomenon is insignificant, taking into account the volume of the reactants.