Life Cycle Assessment as a Tool to Support the Development of a Novel Multifunctional Treatment for Porous Sandstone Conservation

Porous stones are widely used in historical constructions and represent a major component of built cultural heritage. Their conservation commonly depends on multiple single-function products, such as consolidants, hydrophobic agents, biocides, or cleaning agents, which are often toxic and environmentally burdensome. This study performs an environmental assessment of a novel multi-function product designed for the sustainable conservation of porous stones and compares it with other conservation treatment alternatives. This product integrates green chemistry and nanotechnology through a water-based alkoxysilane modified with layered double hydroxide (LDH) particles. Laboratory and field tests on Portuguese monuments demonstrated suitable technical performance, including high substrate compatibility, effective consolidation depth, durable hydrophobicity, biocidal effect, and minimal visual alteration. To evaluate its environmental performance, a life cycle assessment (LCA) was carried out, from cradle-to-grave. The system boundaries encompassed production, application, and transportation stages, with 1 m2 of treated sandstone surface as the functional unit. LCA was performed using CML-IA and ReCiPe methodologies in the SimaPro software. The results revealed the extent of environmental impacts of the novel product, addressing the multi-function strategy compared with conventional products and treatment scenarios. They identified critical life cycle stages for improvement to further enhance environmental performance across scenarios, particularly the influence of perfluorodecyltrimethoxysilane on the environmental burden of the novel product. Overall, this study demonstrates the value of LCA as a design and decision support tool for developing sustainable, multifunctional materials for cultural heritage conservation.