Application Protocol for the Consolidation of Calcareous Substrates by the Use of Nanolimes: From Laboratory Research to Practice

Abstract

Calcareous materials such as limestone and lime-based mortars, widely used in the Built Heritage, are often subjected to degradation processes that can lead to loss of cohesion and material loss. Consolidation of these materials with liquid products via the surface is a common practice; however, the most used consolidation products (e. g. TEOS-based) show a poor physical-chemical compatibility with calcareous substrates. For application on calcareous materials, the so-called nanolimes, i. e. dispersions of lime nanoparticles in alcohols, are an alternative to TEOS-based products, thanks to their chemical compatibility with lime-based substrates. Nanolimes can help to recover a superficial loss of cohesion. However, their in-depth consolidation effect is not always satisfactory. Previous work has shown that a better deposition of lime nanoparticles in depth can be achieved by adapting the properties of the nanolime dispersion (kinetic stability and evaporation rate) to the moisture transport properties of the substrate, through optimization of the solvent. In this paper, freshly synthetized nanolimes were dispersed in pure ethanol and/or in binary mixture of ethanol (95 %) and water (5 %). These nanolimes were applied on Maastricht limestone and on a lime-based mortar by capillary absorption (method commonly used for laboratory tests) and by nebulization (method widely used in situ). The aim of this research is to fill the gap between laboratory tests and on site application, providing an application protocol for restorers and professionals in the field. The research shows that results obtained by application by capillary absorption do not always correspond to those obtained by nebulization. This fact should be considered when deciding on the use of a consolidation surface treatment in practice.

Synthetic calcium carbonate improves the effectiveness of treatments with nanolime to contrast decay in highly porous limestone

“…In fact, the effectiveness might be highly variable in function of the type of stone (in terms of mineralogy and pore network), the nature of the consolidation material, the solvent employed, the application method. Therefore, further studies are underway to test different treatment procedures, like brushing 11,76 or application by capillarity 76 , modifying the solvent composition 4,6,19–21 or applying water after the consolidation treatment 24 .…”

“…similar thermal expansion, elastic modulus, assure similar permeability), long-term stability and performance (avoiding self-deterioration, colour changes, by-product formation) 4,5 . It is therefore not surprising that most of the consolidation agents available on the market show drawbacks and the design of new products is a very active field of research 6–9 .…”

Nanolimes doped with quantum dots for stone consolidation assessment

“…The total carbonatation of the treatment was evaluated by the phenolphthalein test according to Borsoi et al [35]. A solution of 1% phenolphthalein (60% ethanol-40% water) was nebulized over the cross-section of the samples after 20 days of the application of the treatments.…”

Basic Protocol for On-Site Testing Consolidant Nanoparticles on Stone Cultural Heritage

“…Nevertheless, they have not designed a basic protocol to support decision making on the best consolidant for on-site restoration with experimental results. Some guidelines or recommendations can be deduced of the methodologies and results of different papers, especially about application methodologies [28], testing methods [29,30] and consolidant evaluations [31] or aging tests to assess the durability of the consolidants [32]. Nevertheless, it was De Rosario et al [33] who made a substantial difference between laboratory and on-site evaluation.…”