Biological colonization features on a granite monument from Braga (NW, Portugal)

Abstract

The Edificio do Largo do Paco, in Braga, built between 14th and 18th centuries, presents several colored patinas and biological colonization on the facades of the medieval unit.. This chapter describes the study conducted to characterize biocolonization in a façade of the monument to determine the microbiologic activity responsible for the biodeterioration of the granite stone, particularly for its disfigurement. Qualitative and quantitative microbial analyses were done. Complementary mineralogical studies by X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) of the granite substrate were also made. The analyses revealed the existence of a very large and significant range of stone colonizing organisms: biogeochemical nitrogen and sulfur cycles bacteria, algae, fungi, actinomycetae, heterotrophical microorganisms, and sugar fermentative bacteria. This biological colonization is associated with other granite stone pathologies— granular disintegration, scales, flakes, and patinas. Patinas are biogenous, mainly formed by biofilms of algae, cyanobacteria, and fungi that cover the stone creating different colors. Biogenous round particles were identified. Although the salt crystallization is rare, XRD and SEM-EDS analyses allowed the identification of gypsum underlying scales and covered by biogenous layering.