Porosity and water absorption of different binder/aggregate ratios of repair mortar and porous limestone were studied that were used in many Hungarian monuments. Different types of mortars were analyzed by using mercury intrusion porosimetry (MIP) and the water saturation method (WSM). Test results showed that there was a strong correlation between the absorption mechanism and the porosimetric characteristics. Mechanical properties of the tested mortars were observed earlier. Pore size distribution confirms that the total porosity increases with increasing aggregate content. Natural stones mainly have medium and large pore radii (1–100 μm) while repair mortars, even with increased aggregate ratio, have smaller pore radii (0.01–0.1 μm). The comparison of different data allows us to state that pore characteristics such as pore volume, pore geometry, pore size distribution and network connectivity are the key control factors of stone and mortar deterioration.