Protection of gypsum artifacts by Mg(OH)2 based super-hydrophobic nanocomposite

Gypsum has been largely used since ancient times both as a building material and for create sculptural decorations. In recent years, interest in the use of gypsum as one of the most sustainable mineral binders has grown. However, due to its strong water absorption and poor mechanical properties, it is subject to several physical, chemical and biological degradation processes. To improve the durability and water resistance of gypsum-based plaster artifacts, a new hydrophobic nanocomposite treatment for gypsum is proposed, based on a mixture of Mg(OH)₂ nanoparticles with size of about 15 nm and TEOS/PDMS solution (commonly referred to as OrMoSil). The reinforcing and protective properties of the treatment were investigated. The treatment was distributed homogeneously inside and on the surface of the samples. Thermal stability is slightly improved by the treatments. The new hydrophobic coating is very effective as a protective agent against water penetration with a capillary water absorption reduced by 40 %. The super-hydrophobic properties are evidenced by a static contact angle greater than 150° with a wettability behaviour similar to the petal effect. Colorimetric measurements show no colour changes even after repeated artificial aging cycles. When embedded into the plaster, the treatment improves the mechanical resistance with respect to reference gypsum: flexural and compressive strength increase of 59 % and 72 %, respectively, and the dynamic elastic modulus of about 35 %. The new hydrophobic nanocomposite can be proposed for the protection and the improvement of mechanical properties of gypsum artifacts both for restoration of cultural heritage artefacts and for building interest.