Application of Nanolimes for the Consolidation of Limestone from the Medieval Bishop's Palace, Lincoln, UK

Abstract

Nanolimes are the first nanomaterials used in heritage conservation for natural stone consolidation. Thanks to their size, they show good penetration depth into substrates, high reactivity resulting in a faster carbonation process, and the ability to bridge cracks through the formation of a network of calcium carbonate cement. Two commercial nanolimes, CaLoSiL (IBZ Salzchemie) and Nanorestore (CSGI) and a dispersion of Ca(OH)2 nanoparticles, synthesized by an anionic exchange process, were applied to fresh and naturally weathered limestone specimens, previously removed from the medieval Bishop's Palace in Lincoln, UK. A protocol of non-destructive tests was defined to study the treatment effectiveness, both in the laboratory and on-site. The two commercial nanolimes exhibit a low penetration depth, accumulating on the surface and creating a white coating, and lead to only a small increase in surface hardness. On the contrary, the laboratory-synthesized consolidant was able to effect a good superficial consolidation, without affecting the water absorption and aesthetic properties of the specimens. These results, together with those obtained from the application and monitoring of the consolidants on-site, will be crucial for the planning of interventive conservation at the Bishop’s Palace.