In this paper is described principle of hydrophobicity as a function method for increases durability and service life of building materials. Several types of hydrophobic additives, which were applied either to the interior structure or either as a coating on the surface of the element, were tested. In some cases, it was a combination of both. The article is about specific measurement of resistance against alkalis. Higher resistance to alkali and therefore better durability properties show samples with hydrophobic coating than with inner additives. All the samples with inner impregnation exceeded its permitted limits established for the alkali resistance multi-times, i.e. result is in terms of resistance significantly negative.