Nanolime, ethyl silicate and sodium silicate: Advantages and inconveniences in consolidating ancient bricks (XII-XIII century)

Abstract

This paper aims to study the strengths and drawbacks of nanolime, ethyl silicate and sodium silicate coatings in consolidating heritage bricks. Initial X-ray diffraction (XRD), X-ray fluorescence (XRF), and thermogravimetric analyses (TG-MS) showed the bricks are particularly rich in carbonates, although they also contain quartz and minor proportions of halite and gypsum. The consolidants were examined by Transmission Electron Microscopy (TEM); Optical Microscopy (OM) and Scanning Electron Microscopy (SEM); and their effectiveness was tested by non-destructive methods based on colour variation or minimally destructive ones as peeling tests, Shore-A hardness and water permeability tests. The colorimetric properties of bricks were dissimilarly affected by the treatments being ethyl silicate the one that induced the lowest change. It was found that sodium silicate formed hard coatings that were prone to cracks and efflorescence formation after few days of curing. Nanolime and ethyl silicate provided similar consolidation performance, although water permeability was visibly reduced by the latter coating. In contrast, the initial XRD, XRF and TG-MS characterisation of heritage bricks confirmed they are more similar (compatible) to nanolime than the rest of treatments. © 2021 Elsevier Ltd