Modified nanolimes dispersion:structure and colloidal stability

An important part of the Built Heritage is made of calcareous stone and lime-based plasters and renders. When exposed to weathering, these materials may suffer from several degradation processes. Decay patterns, as powdering and/or sanding, can arise and induce a loss of cohesion. Consolidation treatment is a common practice to restore degraded historical materials. Nevertheless, when considering calcareous materials, there is a lack of efficient and compatible consolidants. Nanolimes, i.e. colloidal dispersions of calciumhydroxide, intend to overcome the limitations of traditional consolidants and have demonstrated to properly recover the superficial decohesion. However, nanolimes do not always guarantee a in depth consolidation, necessary e.g. in the case of decayed stone or render. In fact, the high kinetical stability and volatility of the nanolimes inhibit the phase separation of the lime nanoparticles from the alcoholic solvent. A modification of the solvent appears a promising strategy to enhance nanolime deposition in depth. The aim of this research is to study the behaviour of new nanolimes, dispersed in ethanol, isopropanol, butanol or water. The nanosize and morphology of the nanolimes were assessed by SEM-EDS and DLS, and the kinetical stability studied by Uv-Vis spectroscopy; the absorption and drying kinetics of the new nanolimes, applied on Maastricht limestone and lime-based mortars, was measured. The SEM-EDS observations and the DLS analyses show that lime nanoparticles have rounded to hexagonal shape and nano to submicrometric size (70 to 500nm). Compared to nanolime dispersed in ethanol, the new nanolimes in butanol and water have lower kinetical stability and faster drying rate. This is expected to favour the precipitation of nanoparticles in depth.