Preliminary investigations of compatible nanolime treatments on Indiana limestone and weathered marble stone

The conservation of historic structures must be carried out through treatments that use materials which are compatible with the originals. In recent years, nanolime has been considered one of the most promising products for the consolidation of calcareous substrates due to its characteristics of high compatibility with the treated substrate and durability. The effectiveness of nanolime products has been proven for superficial consolidation treatments (e.g. plasters and wall-paintings), and research nowadays is focused on the study of the in-depth consolidation effectiveness of porous substrates. The aim of this paper is to undertake preliminary investigations of compatible nanolime treatments for Indiana limestone (US) and a weathered marble. Nanolime was synthesized by anion exchange resins and dispersed in isopropanol and ethanol. The consolidation effectiveness is assessed by studying changes in porosity, drilling resistance, surface cohesion and aesthetic appearance (colour). Results showed that nanolime yielded the highest consolidation effectiveness when treated samples were kept in high relative humidity environments (~75%RH) or regularly sprayed with carbonated water in a laboratory environment (~50%RH). These results suggest that for an on-site consolidation treatment with nanolime in dry environments, treated surfaces could be regularly sprayed with carbonated water to increase consolidation effectiveness.