Hydrophobic Surface Treatment for the Protection of Carparo Stone

The effectiveness of a hydrophobic coating based on TEOS/PDMS in protecting Carparo stone, a biocalcarenite characterized by high porosity and poor resistance to atmospheric agents and erosion, was evaluated. The hydrophobic treatment was applied over a pretreatment based on PMMA/ZrO2/SiO2 to promote a uniform distribution on the surface. Micro-tomography analyses demonstrate that pretreatment forms a homogeneous coating on the surface. Scanning electron microscopy investigation shows that the hydrophobic treatment based on TEOS/PDMS spreads across the entire surface. The coating is effective in reducing capillary water absorption, and the coated stones exhibit hydrophobicity, achieving contact angles > 140°. The coating has proven esthetically acceptable based on colorimetric tests. The durability of the treatments was evaluated through artificial aging consisting of rain cycles alternating with UV irradiation cycles. The contact angle tests carried out at the end of each cycle demonstrate that the protective coating is not leached and is still very effective. The new sustainable hydrophobic treatment can be successfully proposed for the protection of porous stones.