The dry-to-wet strength ratio of stone known for over 100 years is much simplified by establishing the modulus of rupture with small discs cut from drill cores. A curvilinear relationship was established for crystalline marbles of different stages of weathering; the prediction of rock strength is thus possible on the basis of water sorption. The helerogeneity of sandstones does generally not permit such predictions yet. Testing of thin discs is very useful for the evaluation of the effectiveness of stone consolidants.