Strategies optimization and durability analysis of surface protection technology for ancient architecture red sandstone

Ancient architectural red sandstone (AARS) exhibits high susceptibility to environmentally induced deterioration, necessitating effective protective interventions. However, research on conservation strategies and durability enhancement for AARS remains critically limited. This study addresses this gap by designing five surface protection schemes—incorporating organic, inorganic, and hybrid coatings—to optimize AARS durability strategies. Building upon the optimal protection technology identified, we comprehensively evaluated surface treatment efficacy on both old and new red sandstone specimens through multi-modal analysis using scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultrasonic pulse velocity (UPV) measurements. Results demonstrate that the silica-silane hybrid coating delivered superior protection, yielding a denser microstructure with reduced pore space, a 7.45% UPV increase, and a 75.12% porosity reduction. During 120-day accelerated aging tests, protected new specimens exhibited a 14.17% integrated degradation degree (IDD), while protected old specimens reached 20.05%; untreated new specimens degraded to 29.92%, whereas untreated old specimens underwent complete failure at 85 days. XRD analysis revealed calcite-gypsum transformation and chlorite dissolution in untreated specimens during aging, whereas the optimal coating suppressed calcite dissolution without detectable secondary phase formation. This work establishes a scientifically validated conservation protocol for AARS, providing critical technical support for historical architectural heritage preservation.