STUDIES OF PATINAS AND DECAY MECHANISMS LEADING TO THE RESTORATION OF SANTA-MARIA-DE-MONTBLANC (CATALONIA, SPAIN)

The baroque facade of Santa Maria de Montblanc (Catalonia, Spain) was built of several varieties of calcareous sandstone, with varying clay content. The building materials were studied and their composition was related to the forms of decay and weathering mechanisms. The whole facade is coated with a 'patina', the colour of which ranges from orange to dark brown. Prior to the cleaning of the whole monument, a complete study of the layers forming the patinas was carried out, including the determination of mineral composition, fabric and colour. The biological or man-made origin of the patinas is discussed.