Search

Stone architectural heritage exposed outdoor represents a challenging habitat for biological growths; nevertheless, biocolonization on heritage structure is ubiquitous and represents a major mechanism of alteration. However, the identification of specific microorganisms with known reactivity towards the stone substrate does not necessarily imply that a biodeterioration process is in progress and, in specific conditions, bioprotection effects have been highlighted as a result of colonization. The main objective of the present research is to evaluate the biofilm formation on different lithotypes exposed to similar environmental polluted conditions, and to investigate whether the presence of subaerial biofilms can be associated to an increased magnitude of deterioration of the colonized surfaces with respect to the not colonized ones. In particular, the research examines the extensive biological colonization of the stone surfaces of the façade of the Cathedral of Monza (Italy). Four metamorphic stones widely used in the façade and showing rather different compositional, mineralogical and microstructural features were studied. The state of conservation of the stones was characterized under the mineralogical and compositional point of view by X-ray diffraction and Fourier Transformed infrared analysis. The microstructure of colonized substrates and of reference not colonized ones was studied by means of optical and electron microscopy, to comparatively evaluate the damage extent and weathering patterns in both conservative conditions. The structure and the architecture of biofilms growing on different lithic surfaces were investigated by CLSM in both fluorescence and reflection modes. Captured images were analyzed for 3D reconstructions of biofilm samples. The biovolumes were also calculated to estimate the total biomass. The results indicate that the four lithotypes showed different colonization extents. However, even in presence of extensive biological growth, chemical-physical deterioration mechanisms caused by environmental exposure were largely responsible for deterioration. A relationship between compositional and surface morphological features and biocolonization was also observed., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The study characterized the sessile microbial communities on mortar and stone in Milan University's Richini's Courtyard and investigated the relationship between airborne and surface-associated microbial communities. Active colonization was found in three locations: green and black patinas were present on mortar and black spots on stone. Confocal laser scanning microscopy, scanning electron microscopy and culture-independent molecular methods revealed that the biofilm causing deterioration was dominated by green algae and black fungi. The mortar used for restoration contained acrylic and siloxane resins that could be used by microorganisms as carbon and energy sources thereby causing proliferation of the biofilm. Epifluorescence microscopy and culture-based methods highlighted a variety of airborne microflora. Bacterial and fungal counts were quantitatively similar to those reported in other investigations of urban areas, the exception being fungi during summer (1-2 orders of magnitude higher). For the first time in the cultural heritage field, culture-independent molecular methods were used to resolve the structure of airborne communities near discoloured surfaces, and to investigate the relationship between such communities and surface-associated biofilms.

Surfaces are continuously exposed to physical, chemical and biological degradation. Among the biological agents that cause deterioration, microorganisms are of critical importance. This work is part of a research programme for the characterisation of the alterations of the Milan Cathedral (Italy). Four stone samples of the Milan Cathedral were chemically analysed and the microbiological growth assessed. X-ray diffraction (XRD) showed that calcite was always present in each sample and one sample was also characterised by the chemical form of alteration gypsum. Using Fourier Transform Infrared Spectroscopy (FTIR) together with Scanning Electron Microscopy (SEM), it was possible to prove that the samples were consolidated with the synthetic acrylics and epoxy resins. The green-black biological patinas of the specimens were studied using cultivation, microscope observations and a method for single-cell detection. Sampling for fluorescent in-situ hybridisation (FISH), with ribosomal RNA targeted oligonucleotide probes, was also performed using adhesive tapes. The bulk of the prokaryotes were Bacteria but some Archaea were also found. The bacterial cells were further characterised using specific probes for Cyanobacteria, and alpha-, beta-and gamma-Proteobacteria. In addition, black fungi isolated from the stone and the fungi of the standard ASTM G21-96(2002) method were employed to test if the detected synthetic resins could be used as the sole source of carbon and energy. One isolated Cladosporium sp. attacked the freshly dried acrylic resin. Results show that the detected bacteria and fungi can cause severe damage both to the stone monument and its synthetic consolidants.

Monuments and artistic stone surfaces are often consolidated and protected with synthetic polymers, in particular, acrylics. Although it is generally thought that acrylic polymers are resistant to biodeterioration, we report for the first time the systematic occurrence of dematiaceous meristematic fungi on many marble samples of the cathedral in Milan (Italy) previously treated with this material. Fourier transform infrared spectroscopy applied to the Milan cathedral stone samples revealed characteristic features of biodeteriorated synthetic resins that differentiated them from the aged but nonbiodeteriorated samples. Samples showing biological colonization were analyzed for the presence of fungi. Cultivation and morphological characterization and methods independent from cultivation, such as denaturing gradient gel electrophoresis coupled with partial 18S rRNA gene sequencing and immunofluorescence staining with melanin-binding antibodies, showed that melanin-producing species are heavily present on stone surfaces protected with acrylic resins. This observation raises the question of the effectiveness of acrylics in protecting stone artworks.

Abstract: The direct recording of the water presence in stone materials or in masonry provides information about their state of conservation and it can also indirectly reveal the effectiveness and durability of protection treatments or chemical interventions for rising damp reduction. Evaluating the humidity, i.e. the water content, of a building material is a problematic issue because the water is distributed in a large volume in different amounts. Usually these kinds of measures have been carried out with resistance/conductivity and thermographic systems, which are all affected by weaknesses and intrinsic restrictions. Thermographic investigations are affected by temperature differences and the evaporation–cooling effect. In the case of electric measures, the signal does not originate from the water present, but from the conductivity of the water itself, which is strictly connected to the presence of ion species that can modify it significantly. Moreover, interruptions, like air gaps or fractures, cancel the signal. For both methodologies the quantitative water evaluation is difficult. Although some minerals, like iron-based ones, could disturb the NMR measure, the signal is not influenced by the presence of most common soluble salts or pollutants in the solution (such as nitrates, chlorides or sulphates) and it is only generated by the number of water molecules present in the sensitive volume. In this paper the results, obtained in the laboratory with a portable NMR device, developed within the framework of the Eureka Project E!2214-MOUSE, are shown. The encouraging results obtained in this preliminary experiment, concern mainly the investigation of stone materials that have different porosimetric features and the calibration of the instrument under different working conditions. The experiments focused on the correlation between the content of water absorbed by capillarity and the NMR signal intensity obtained by this device. Different materials have been investigated, such as calcarenite and bricks. The experimental work will define a starting platform to successfully transfer the analytical procedure from the laboratory to in situ measurements. [Copyright &y& Elsevier]

• A modelling approach for predicting the sorptivity of porous stones is presented. • The proposed methodology only involves minimal sampling of stone materials. • The model also simulates the water absorption reduction in treated stones. This study aims at validating an easily implementable and effective methodology to simulate the capillary imbibition rate of porous building materials, with special attention to stones employed in historical architecture. Two models selected from the literature are discussed from both a theoretical and practical viewpoint and their effectiveness in describing the imbibition process is evaluated on a large set of water absorption data of four different natural stones. It is shown that these models can be used in a predictive way to calculate the sorptivity of stones with fairly good approximation. Furthermore, they may represent a useful tool for the study of porous materials of built heritage, since, contrary to standard tests for sorptivity determination, they only require small samples to determine the pore size distribution and the maximum water saturation of the investigated materials. Finally, it is shown that the same models can also be used to simulate the reduction in water absorption after the application of water-repellent products, affording some insight into the protection mechanism and the criteria that determine the performance of protective treatments. [ABSTRACT FROM AUTHOR]