Preparation of Highly Crystalline Nano Ca(OH)2and Its Comparative Assessment with Commonly Used Materials for the Protection of Wall Paintings

Abstract Due to the ecocompatibility with carbonate‐based substrates, Ca(OH) 2 nanoparticles are currently used for cultural heritage conservation such as wall paintings. However, the nano Ca(OH) 2 still suffers from different forms and poor uniformity, limiting its application potential. Also, there is a lack of systematic comparative studies between nano Ca(OH) 2 and the commonly used wall painting reinforcement materials. In this study, homogeneous hexagonal nano Ca(OH) 2 particles with a size of ≈100 nm are successfully prepared through the convenient chemical liquid phase method and by utilizing surfactants to control the growth. The resulting nano Ca(OH) 2 is less agglomerated and has superior crystalline morphology, prolonged suspension time, and more suitable carbonation time in comparison to commercial Ca(OH) 2 materials. Additionally, the reinforcement effect of the resulting nano‐Ca(OH) 2 with that of the commonly used pigment layer reinforcement materials such as AC33, B72, Tetraethyl orthosilicate, WPU (Waterborne polyurethane) and commercial Ca(OH) 2 is systematically compared. The synthesized nano Ca(OH) 2 penetrated wall painting blocks to a depth of 683 µm, three times deeper than commercial Ca(OH) 2 , achieving moderate color deviation, higher flexural strength (0.529 MPa), and bond strength (1.105 mg cm −2 ), thus highlighting its potential in wall painting reinforcement and expanding its application scope.