Covering Layers on Granite Buildings of Northwestern Iberian Peninsula: When Observable Characteristics and Lab Characterization Do Not Match

Illustrated glossaries on stone pathologies help to describe deterioration forms in built heritage without resorting to any laboratory analyses. In this way, terms such as crust, deposit, and soiling which according to ICOMOS-ISCS: Illustrated Glossary on Stone Deterioration Patterns may include exogenic material, a patina which results from ageing of the material in an endogenous process, and a film included under the broad term of a coating layer in the glossary, can be macroscopically identified on site. However, a definition on the basis of characteristics only observable with the naked eye (without further analysis in the laboratory) is certainly complicated, and if in addition, the case studies are on granitic rock (a major building stone used across Europe), the picture becomes even more complicated. The intention of this brief report is to engender an open, constructive debate about the casuistry of the covering layers on granite (a poorly reactive and less porous rock) and the difficulty of using the ICOMOS nomenclature on them.

Deterioration-Associated Microbiome of Stone Monuments: Structure, Variation, and Assembly

ABSTRACTResearch on the microbial communities that colonize stone monuments may provide a new understanding of stone biodeterioration and microbe-induced carbonate precipitation. This work investigated the seasonal variation of microbial communities in 2016 and 2017, as well as its effects on stone monuments. We determined the bacterial and fungal compositions of 12 samples from four well-separated geographic locations by using 16S rRNA and internal transcribed spacer gene amplicon sequencing.Cyanobacteriaand Ascomycota were the predominant bacterial and fungal phyla, respectively, and differences in species abundance among our 12 samples and 2 years showed no consistent temporal or spatial trends. Alpha diversity, estimated by Shannon and Simpson indices, revealed that an increase or decrease in bacterial diversity corresponded to a decrease or increase in the fungal community from 2016 to 2017. Large-scale association analysis identified potential bacteria and fungi correlated with stone deterioration. Functional prediction revealed specific pathways and microbiota associated with stone deterioration. Moreover, a culture-dependent technique was used to identify microbial isolates involved in biodeterioration and carbonatogenesis; 64% of 85 bacterial isolates caused precipitation of carbonates in biomineralization assays. Imaging techniques including scanning electron microscopy with energy-dispersive spectroscopy, X-ray diffraction, and fluorescence imaging identified CaCO3crystals as calcite and vaterite. Although CaCO3precipitation induced by bacteria often has esthetically deleterious impacts on stone monuments, this process may potentially serve as a novel, environmentally friendly bacterial self-inoculation approach to the conservation of stone.IMPORTANCEComprehensive analyses of the microbiomes associated with the deterioration of stone monuments may contribute to the understanding of mechanisms of deterioration, as well as to the identification of potentially beneficial or undesirable microbial communities and their genomic pathways. In our study, we demonstrated thatCyanobacteriawas the predominant bacterial phylum and exhibited an increase from 2016 to 2017, whileProteobacteriashowed a decreasing trend. Apart from esthetic deterioration caused by cyanobacteria and fungi, white plaque, which is composed mainly of CaCO3and is probably induced byCrossiellaandCyanobacteria, was also considered to be another threat to stone monuments. We showed that there was no significant correlation between microbial population variation and geographic location. Specific functional genes and pathways were also enriched in particular bacterial species. The CaCO3precipitation induced by an indigenous community of carbonatogenic bacteria also provides a self-inoculation approach for the conservation of stone.

STONE DETERIORATION CHARACTERIZATION FOR ITS CONSERVATION

The conservation of stone is fundamental for the preservation of our architectural and monumental heritage. Although stone is reputed as one of the most resistant materials, there are many factors that contribute towards its deterioration. This paper aims to summarize the main deterioration factors, such as air pollution, the presence of soluble salts, and biocolonization. A brief discussion of these factors serves as the basis to introduce the importance of a correct diagnosis regarding the origin of the observed deterioration. Only then, can the most appropriate solution be found to address the problem.Keywords: stone nature, deterioration, conservationResumo:CARACTERIZAÇÃO DA DETERIORAÇÃO DAS PEDRAS PARA A SUA CONSERVAÇÃO. A conservação da pedra é fundamental para a preservação do nosso património arquitectónico e monumental. Embora seja um dos materiais mais resistentes, deve-se considerar que existem muitos factores que podem contribuir para a sua deterioração. O presente trabalho sintetiza os principais factores de deterioração, tais como a poluição atmosférica, a presença de sais solúveis e a biocolonização. Uma breve resenha destes factores serve de base para salientar a importância de fazer o diagnóstico correcto da origem da deterioração observada. Só então se pode encontrar a solução mais adequada para resolver o problema.Palavras Chave: tipo de pedra, deterioração, conservação.

Exposure Factors Influence Stone Deterioration by Crystallization of Soluble Salts

The present work tries to determine the factors that influence the crystallization of soluble salts in the stone material used in the construction of buildings in Valencia (Spain). Samples are obtained from a building which has served to accomplish observations and laboratory experiments necessary in order to determine the pathology of deterioration of the material. It was particularized in the exposition conditions of the material as a base for determining the morphologies of deterioration caused by salts in the same lithotype. The main contribution is the petrological study from the architectural point of view considering its orientation, sunlight in façade, and so forth. This study proves that both material petrology (its mineralogy and texture) and the properties related to the movement of water inside rocks play a decisive role in the conservation and development of elements in the alteration.