Search Results (16)

This work evaluates the effectiveness of various consolidating treatments applied to Pugliese tuff (Gravina Calcarenite). This type of stone has been used in numerous historic buildings in the Puglia area (southeast of Italy), which presents durability problems due to high porosity, low cohesion between clasts, and low mechanical resistance. Eco-friendly treatments that generate CaCO₃ have been selected, specifically bioconsolidant KBYO biological and lime water, which a priori are capable of consolidating without occluding the pores or reducing them excessively, thereby creating compounds similar to those contained in the stone and being respectful of the environment. Nano-sized treatments have also been tested, including nanosilica and nanolime, to compare results with eco-friendly treatments. The bioconsolidating treatment has been applied in two different ways, the usual way consisting of two applications a day for 7 days, as well as a double treatment that is applied in two batches of 7 days with a rest of 7 days between applications. Double treatment has shown a great improvement in consolidation compared to the usual 7-day application; this treatment has obtained the best results in both mechanical and petrophysical properties. This study not only demonstrates the effectiveness of the bioconsolidant but also expands eco-friendly conservation strategies to improve the preservation of historical structures built in calcarenite. Full article

There is no doubt that nanotechnology and nanoscience open new doors to new applications and products that can potentially revolutionize the practice field and how we conserve built heritage materials. However, we are living at the beginning of this era and the potential benefits of nanotechnology to specific conservation practice needs are not always fully understood. This opinion/review paper aims to present reflections and answer a question that we are often asked when working directly with stone field conservators: why should we use a nanomaterial instead of a conventional product? Why does size matter? To answer this question, we revise the basic concepts of nanoscience with implications for the built heritage conservation field. Full article

Nanolimes have been commercially available for over a decade as a remineralization agent for natural stone to combat deterioration. While they have been applied successfully and studied extensively, their penetration abilities in different materials have not yet been readily quantifiable in situ and in real time. Using two transparent pore-imitating test systems (acrylic glass (PMMA) and polydimethylsiloxane (PDMS)) and light microscopy, the penetration coefficients (PCs) of two nanolimes (CaLoSiL (CLS) and Nanorestore Plus (NRP)), as well as their solvents, were determined experimentally in square channels of about 100 µm diameter. Their PCs and those for a previously published glass–resin-based test system were also predicted based on measurable material parameters or literature values using the Lucas–Washburn equation. Additionally, a liquid mineral precursor (LMP) of calcium carbonate based on complex coacervation (CC) was investigated as an alternative to the solid particle dispersions of nanolime. In general, the dispersions behaved like their pure solvents. Overall, trends could be reasonably well predicted with both literature and experimentally determined properties using the Lucas–Washburn equation. In absolute terms, the prediction of observed infiltration behavior was satisfactory for alcohols and nanolimes but deviated substantially for water and the aqueous LMP. The commercially available PMMA chips and newly designed PDMS devices were mostly superior to the previously published glass–resin-based test system, except for the long-term monitoring of material deposition. Lastly, the transfer of results from these investigated systems to a different, nontransparent mineral, calcite, yielded similar PC values independently of the original data when used as the basis for the conversion (all PC types and all material/liquid combinations except aqueous solutions in PDMS devices). This knowledge can be used to improve the targeted design of tailor-made remineralization treatments for different application cases by guiding solvent choice, and to reduce destructive sampling by providing a micromodel for pretesting, if transferability to real stone samples proves demonstrable in the future. Full article

This work aims to reveal the recent research trends in the consolidation of stone-built heritage and discuss the advantages and drawbacks of the options and strategies followed by researchers over the last 10 years. Peer-reviewed articles were used to build a database and analyze the details of the stone samples (chemical nature, type of voids, and condition), treatment protocols (application methods and consolidation products), and testing methods to assess the strengthening results of the treatments. In addition, the reported increments in the mechanical properties were also examined to reveal the strengthening capabilities of recent consolidation treatments. The statistical treatment of the results allowed pinpointing the stone varieties that need more frequent consolidation actions (limestone, biocalcarenite, and sandstone) and the aspects that make them more difficult and riskier. Other tendencies were discussed, for example, the predominant use of sound samples over decayed samples (61% vs. 39%) or the predominant use of alkoxysilanes (~46%) over other families of consolidants (e.g., nanolime, ~21%). The current consolidation treatments were found to improve stone strength; however, the most problematic issue in state-of-the-art is the difficulty of identifying high-risk situations of over-consolidation or poor distribution in depth because of either the lack of testing or limitations of the various assessment techniques. Full article

The effects of the double and the multiple application (2 to 6) of Calosil^® (IBZ-Salzchemie GmbH, Halsbruecke, Germany) E25, IP 25 and E50 products were studied on Maastricht limestone, which is characterized by high porosity and large pores. Both destructive and non-destructive laboratory tests we performed in order to assess the consolidating efficiency of the nanolimes—the bending and compressive strengths, ultrasound velocity measurement, porosity determination and SEM examination. Except for the compressive strength, the other characteristics were investigated in the depth profile of stone specimens to find the distribution of the treatment product within the substrate. The performed tests showed good penetration of CaLoSiL nanolime products into the studied limestone. The bending strengths of limestone samples after double treatment using nanolime E 25, IP25 and E 50 were found to be increased by 50%, 44% and 89%, respectively, whereas the compressive strength increased by 50%, 23% and 73%. The porosity of the stone was reduced by the treatment, but only slightly, to an acceptable extent. The higher sum of performed nanolime applications resulted in a higher strengthening effect but at the same time at the uneven distribution of the product in the stone specimen, which was followed by an increase in the strength and decrease of open porosity in the surface part. SEM examination showed a modification of the stone microstructure by the added binder. Full article

Consolidation of mural paintings in hypogea is challenging because of their severe microclimatic conditions, characterized by high humidity levels, low air circulation, the presence of salts efflorescence, and the detrimental growth of biodeteriogen agents. Traditional consolidant products show significant drawbacks when used in hypogeum. Organic compounds, such as acrylic emulsions, are bio-receptive and some inorganic consolidants, such as silica-based products, show a lack of compatibility with the original substrate, which could lead to a reduction in permeability and an increase in the mechanical resistance of the external layer. The presence of solvents in their formulations, particularly short-chain alcohols that can activate germination of fungal spores, leads to the release of great amounts of volatile organic compounds, which are particularly harmful in the hypogeic environment. To solve these problems, restorers of the Istituto Centrale per il Restauro (ICR) decided to use a new aqueous nanolime dispersion, NANOLAQ, consisting of pure and crystalline Ca(OH)₂ nanoparticles dispersed in water, produced by an innovative and sustainable patented procedure. After laboratory testing, the product has been applied on site, on a medieval mural painting in the Ss. Peter and Paul hypogeum in the UNESCO site of Matera (Italy), monitoring the performance in terms of cohesion of the paint layer and preservation of aesthetic features. Full article

This paper reports the preliminary results of a comparative analysis of the effects of three consolidants on the color appearance of fresco paint layers affected by lack of cohesion. In vitro assays were performed with a laboratory-synthesized nanolime, a commercial nanolime (CaLoSiL^® IP25), and a commercial acrylic resin (Primal^TM SF-016 ER^®) applied by nebulization over two sets of replicas of buon and lime fresco painted with red and yellow ochres and smalt pigments. The paint layers were surveyed before, one week, and one month after treatment with technical photography in the visible range (Vis) and ultraviolet-induced fluorescence in the visible range (UVF), as well as optical microscopy (OM-Vis), colorimetry, spectrophotometry, and scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDS). Experimental work also comprised the synthesis of nanolime and its characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetry analysis (TGA-DTG). The results show no alteration on pigments’ spectral curves and elemental composition. The increase in the CIEL* coordinate and ∆E color variation noticed after the treatment with the nanolimes is associated with a white haze formation on the paint surfaces. The impact on color appearance is higher on the darker tones. Full article

During the last decades, the discovery of nanolime and its introduction in the field of Cultural Heritage has entailed a significant advance for the consolidation of historic wall paintings. Nevertheless, its use is not completely generalized yet within the conservation practitioner’s community due to its undesired white veiling deposit on the surface after treatment which usually covers the pictorial layer. Given the scarcity of existing literature which specify how to mitigate this undesired side-effect, the aim of this work is to carry out the first assessment of possible cleaning and treatment methods to eliminate those deposits and, at the same time, to analyse their effects on the consolidation properties. To do that, we have developed laboratory fresco wall paintings specimens. After applying an artificial ageing cycle to all of them, we consolidated them with CaloSil IP25, one of the most currently used commercial product in the practice. The elimination of the whitish deposits has been investigated with different methods: (1) wiping off the superficial excess of product immediately after each application during the treatment; (2) mechanical cleaning (scalpel) after consolidation; chemical cleaning with rigid gels of water (3), ethylenediaminetetraacetic acid (EDTA) (4) and citric acid (5) after consolidation. The effectiveness of each cleaning method has been assessed by non-destructive methods before and after the consolidation, and repeated after cleaning, by measuring differences in colour, water absorption by capillarity (i.e., sponge test), superficial adhesion (i.e., Scotch Tape Test) and by quantifying the thickness of the deposits eliminated by means of photogrammetry. Results show that both the mechanical cleaning and the removal of the excess of product after each application during the treatment yielded the most promising results for conservation practice. Full article

Neutron radiography (NR) was here applied to study the effects of two different commercially available consolidants on the water absorption properties in a particular type of limestone (biocalcarenite), known as Pietra d’Aspra stone, which is one of the most extensively used lithotypes in Sicilian Baroque buildings. Our attention was mainly focused on the evaluation, using a fast and nondestructive visualization of water motion through capillarity, of the effectiveness of such layers as consolidating agents in view of preserving and maintaining both old and modern structures. The biocalcarenite was treated with nanosilica (Nano Estel^®) and nanolime (CaLoSil^®) by brushing it until full saturation, and then artificially weathered by salt crystallization and temperature/relative humidity jumps. Liquid distribution and height of the water front were monitored as a function of time. Significant differences in the water suction behavior among all the investigated samples were highlighted, which allowed us to gain insight into the coating/substrate interaction mechanisms which regulate the fluid mobility inside the porous network of the limestone. Full article

In the present review paper, the term “effectiveness” of nanolime consolidants was redefined by presenting a suite of efficiency parameters/material properties that must be assessed in order to compare available treatments for weathered calcareous stones for historic buildings. Assessment tools in the form of characterization methods for synthetized nanolime dispersions, artificial weathering techniques, and treated calcareous stones were correlated and discussed, giving rise to non-destructive testing methods. The effect of the application method and dispersion medium was also presented. It was concluded that the presented suite of efficiency parameters and characterization techniques can be applied to further studies for the development of mass consolidation procedures in order to reach penetration depths well beyond the 5.5 cm threshold achieved up to date. Full article

Currently the application of consolidants based on nanoparticles is common practice among restorers. Consolidants should not modify the properties of original materials according to international recommendation, which requires previous studies to decide the optimal option. The selection must be based on empirical results, and not only in the expertise of the restorer, because the consolidant’s effectiveness is influenced by its own properties and other factors such as the characteristics of the artwork (elemental composition, porosity, texture, etc.) and its context (temperature, relative humidity, etc.). Moreover, new protocols must be sustainable and compatible with on-site restoration. A new protocol to test consolidant nanoparticles has been designed and assessed. This is based on easy trials and low-cost techniques—digital microscope, colorimeter, peeling test and ultrasound—that could be employed by restorers in situ. In this paper, different consolidant nanoparticles were tested on stones from two historical quarries. The first treatment was SiO₂ nanoparticles, and the second, a new nanocomposite of Ca(OH)₂ and ZnO quantum dots that allows us to measure penetration depth easily and discern the treated areas under UV lights. This second treatment was the best option for the studied stones, validating the protocol designed for the choice of consolidants. Full article

Protecting stone buildings from weathering and decay is a major challenge in the conservation of built heritage. Most of the stone consolidants currently available are well suited to silicate stones, but are less compatible with limestone. In this paper we present for the first time the results over a 4-year period of various consolidation treatments carried out using nanolime on 6 of the most representative and significant stones used in historic buildings in the United Kingdom. Tests investigated the influence of stone type, environmental conditions and pre-treatments on the effectiveness of the consolidation treatment. A comprehensive and rigorous testing programme was carried out to evaluate the short (12 weeks) and longer-term (4 years) effects. Stone samples were characterised before and after treatment using light and electron microscopy, sorptivity tests and a novel methodology employing drilling resistance to interrogate the near surface effects. Results show that for some of the stones, such as Clunch and Bath Stone, the positive effect of the treatment with nanolime is noticeable after 4 years since application. However, results for other stones such as Portland and magnesian limestone showed that the initial beneficial effect of the treatment is reduced after 4 years. Nanolime treatment of Ham Stone produced an unnoticeable effect on the continuous natural reduction of the drilling resistance of the specimen over time. The results presented are of immense value to conservators as they provide essential guidance on the most appropriate repair approach. Impact to the conservation industry will be to avoid the use of nanolime on stones where there is no perceivable benefit, reducing the risk of adverse effects, including potential damage to buildings. In additional costs will be saved which might otherwise have been spent on ineffective treatments. Full article

This paper presents the results of a laboratory experimentation carried out on stone materials in the framework of the CRATI project (Knowledge and Restoration through Advanced Integrated Technologies) aimed at testing new products with consolidating properties by means of an integrated methodological approach. After the preliminary characterization of stone materials collected in the pilot site, the second stage of the activities within the project were focused on the formulation and testing of products for the conservation of the same materials against decay, especially salt crystallization, one of the most aggressive and common degrading processes. The San Domenico Church, located in the old town of Cosenza (Calabria, Southern Italy) has been chosen as the pilot site and for the in situ tests. Several specimens with the same features of the stone materials used in San Domenico church were collected from a historical quarry near the city of Cosenza. These specimens were treated and then artificially degraded by salt crystallization tests in order to evaluate their susceptibility to weathering intensity. Three different consolidating products were used; respectively, two commercial and another one formulated in laboratory: (a) a suspension of nanosilica (Nano Estel^®); (b) a suspension of nanolime (CaLoSiL^®), and (c) a suspension of nano calcium-hydroxide dispersed in isopropyl alcohol and then mixed with diammonium hydrogen phosphate. A systematic approach, including minero-petrographic, geochemical and physico-mechanical techniques, was applied to evaluate (a) the nature and main features of materials; (b) the efficacy of consolidating treatments, and (c) the resistance of treated stone to the salt crystallization processes. The tested products demonstrated a significant efficiency to consolidate and protect stone material samples, enhancing their resistance to salt crystallization. Thus, such a case history may be useful in order to plan appropriate restoration interventions that consider the interactions between the building stone and the protective/consolidating product. Full article

Calcium ethoxide nanosuspension, a consolidating product developed during the European Nanomatch project, is here modified by adding two different solvents, 2-butanol and n-butylacetate, chosen for their different boiling points with respect to ethanol, the solvent employed in a previous work to dilute the original product. Fourier transform infrared spectroscopy (µFT-IR) was used to understand how the presence of these new solvents can influence the kinetics of the carbonation process and the pathway reaction. Furthermore, coatings derived from nanosuspensions were maintained for specific time intervals at controlled relative humidity conditions (RH = 50% and RH = 90%); the formed mineralogical phases were characterized by µFT-IR and X-ray diffraction (XRD). Results indicate that the used solvents can influence the kinetic and reaction pathways, while the phases formed at the end of the carbonation process are influenced by both solvents and RH conditions. The effectiveness of calcium ethoxide based product diluted in 2-butanol and n-butylacetate as limestone consolidants was evaluated with drilling resistance measurement system (DRMS) and ultrasound pulse velocity (UPV). The impact on color coordinates was also assessed. The results were compared with those obtained with the same product diluted in ethanol and a commercial nanolime. The use of these solvents gave different and better results in terms of efficacy. Full article