A novel multifunctional water-based formulation and new particle-modified variants: Effects on porous stones

This work investigates the potential of a novel water-based fluorinated siloxane formulation, as well as newly developed particle-modified variants incorporating layered double hydroxides (LDH), zinc oxide (ZnO), or silica (SiO 2 ) particles, as multifunctional solvent-free products for the conservation of built-heritage stone. Particles were explored to enhance the performance and multifunctionality of the novel formulation. A multi-analytical, conservation-oriented approach was employed, combining efficacy assessments (consolidation, hydrophobicity, and self-cleaning) and the evaluation of potential adverse effects in the validation of the formulations. The particle-free water-based formulation exhibited good penetration into porous stone substrates, effective consolidation, and the ability to impart hydrophobic surfaces in both studied porous stones, while largely preserving vapor transport properties and inducing minor visual alterations. The addition of LDH particles enhanced consolidation potential and led to the formation of horizontally oriented particle agglomerations at the surface, attributable to their plate-like geometry. Hydrophobicity was not compromised, and limited impact on internal stone pore structure or transport properties were observed. The novel formulation with SiO 2 nanoparticles introduced micro-scale roughness, yielding superhydrophobic and self-cleaning behaviour on rougher substrates, while maintaining depth consolidation and balanced overall performance. In contrast, ZnO nanoparticles markedly accelerated the formulation reactions, reducing its stability and penetration capacity, which limited its consolidation performance despite the achievement of hydrophobic surfaces. Overall, the novel particle-free formulation exhibits multifunctional character and can, per se, serve stone conservation purposes. Moreover, it can be tailored with particles to introduce/enhance new functional effects, if interactions among the particles, sol-gel chemistry, and substrate characteristics are carefully controlled.