Permeability to water vapour in granitic rocks. Application to the study of deleterious effects of conservation treatments

We determined the permeability to water vapour of three granites from the region of Galicia in northwest Spain, before and after treatment with water repellents, with the aim of evaluating the usefulness of this property as a standard descriptive parameter for granites used in construction, and as an indicator of the deleterious effects of water-repellent treatments. Our results indicate that pre-treatment permeability to water vapour varies markedly not only among test slabs cut in different orientations, but also among test slabs cut consecutively from the same sample in the same orientation; in other words, the material is anisotropic as regards permeability, and permeability is strongly dependent on small-scale textural and structural heterogeneity. This clearly makes it difficult to reliably determine the permeability of a given granite. Results obtained with test slabs after treatment with the water repellents Tegosivin or Siliker indicate that such treatment in most cases modifies permeability; however, the high variability among slabs means that these findings should be interpreted with caution.