Three sandstones (Villamayor, Somió, and Tazones) and two dolomites (Laspra and Boñar) used in the construction of various historic Spanish monuments have been selected to study the relationships between porosity, capillary suction, and their petrographic characteristics. Good linear, direct correlations between open porosity, coefficient of capillarity and alterability have been found in the sandstones studied. It has also been observed that the nature, abundance, and disposition of clay minerals of the matrix control, to a great extent, the above mentioned parameters.