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 r egion 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 a n indicator of the deleterious effects of water-repellent treatments. Our r esults indicate that pre-treatment permeability to water vapour varies mark edly not only among test slabs cut in different orientations, but also amon g 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 h eterogeneity. This clearly makes it difficult to reliably determine the per meability of a given granite. Results obtained with test slabs after treatm ent with the water repellents Tegosivin or Siliker indicate that such treat ment in most cases modifies permeability; however, the high variability amo ng slabs means that these findings should be interpreted with caution. (C) 2000 Elsevier Science Ltd. All rights reserved.