Sandstone and limestone can be affected by frost, temperature cycles, salt crystallization and sulphur oxide air pollutants. The effects of these different types of attack can be similar; the formation of sulfate crusts causes narrowing of open pores and the damage caused can resemble that caused by frost action. The outer and inner weathering crusts of buildings have been analyzed quantitatively by energy dispersive x-ray analysis in a scanning electron microscope. The position of the stone on a building can be shown to affect the composition of the weathering crust. The criteria for durability are discussed.