RAPID BIOLOGICAL COLONIZATION OF A GRANITIC BUILDING BY LICHENS

The Galician Centre of Contemporary Art (Santiago de Compostela, Spain ) is a large, modern building finished with a granitic cladding. Compl eted in September 1993, it is already showing signs of deterioration, including biological colonization and intense blackening of exterior s urfaces, and the breaking off of cladding. In this work we investigate d the causes of this premature deterioration. Biological colonization was most intense on the lower areas of shaded walls, the most abundant organisms being the lichens Trapelia coarctata and T. involuta. The b lackening was chiefly due to the build up of microorganisms or their r emains (no elements indicative of atmospheric pollution were detected) . Both the cladding and granite from the source quarry showed signs of severe weathering (fissuration, high porosity, the presence of kaolin ite) and had high capillarity, rapidly absorbing large amounts of wate r and releasing it only slowly. Because of this and the wet climate in Santiago the cladding was almost permanently damp, which, together wi th its weathered condition, made it highly bioreceptive and, at the sa me timer reduced its mechanical resistance, making it susceptible to b reakage. (C) 1997 Elsevier Science Ltd. All rights reserved.