Decay patterns of granite stones in Braga monuments (NW Portugal)

The decay features of thirty-nine monuments built with granite stones and presenting diverse architectural characteristics, date of construction and environment characteristics (including exposition conditions, traffic intensity, etc) are compare in order to discuss decay patterns and susceptibility of granite types applied in architectural works. Decay patterns of biotite-rich medium to fine-grained (frequently porphyritic) granite stones are related to weathering inherited from the quarry (expressed by yellowing), to the presence of heterogeneous elements (enclaves and phenocrysts) and to grain size variations. Fine-grained leucogranitic stones decay is mainly controlled by tectonic foliation. The characteristics of stone application, including how and where was stone used, influence decay patterns by favouring salt pollution concentration, biological colonisation and fixation of atmospheric pollutants. Erosive decay features (linked mainly to salt pollution) and stone coatings (linked to biological action and atmospheric and organic pollution) are widespread decay forms that affect granite stones on Braga buildings. 364 Historical Constructions