EN
A prevailing mechanism of the chemical weathering of bricks exposed to the polluted atmosphere of central Cracow is an uptake of sulphur dioxide by a solution of calcium carbonate abundant in the mortar. The subsequent cycles of dissolution, transport and precipitation lead to filling cracks and cavities in the bricks with gypsum as well as to the formation of relatively thin gypsum crusts on the surface. The latter, always incorporating soot and dust particles, constitute a characteristic black patina of the brick buildings. The effectiveness of water repellent treatment in protecting the lime surfaces against acid deposition has been demonstrated by using artificial weathering in a humid atmosphere containing SO2 .