Calcium hydroxide nanoparticles coatings applied on cultural heritage materials: their influence on physical characteristics of earthen plasters

Abstract Calcium hydroxide nanoparticles (nanolime) are a novel solution for consolidating clay-based plasters and adobes in cultural heritage constructions. The suspension is applied as a coating and fully compatible with calcareous earthen materials. Ca(OH)2 nanoparticles (NPs) are transformed into protective CaCO3 coatings due to a carbonation reaction. This work aims to study the effectiveness of Ca(OH)2 NPs coatings in protecting the surface of earthen plasters. To do this, the effect of nanolime on surface consolidation, water permeability and durability in front of rain action is evaluated. It was found that the treatment improved the superficial cohesion and reduced water permeability of plasters due to formation of calcareous coatings due to partial obstruction of pores on the surface. In contrast, the effectiveness of the treatment is not demonstrated against rainwater and acid environments (HCl). Finally, acid rain simulation (H2SO4) led to deposition of protective films of gypsum that might delay the plaster deterioration in the long term.