Effects of accidental staining in carbonate stones: physical, chemical and mineralogical changes

Abstract

Two carbonate stones (a limestone and a marble), commonly used for flooring, wall cladding and countertops, were exposed to different staining agents. After each cycle (staining and cleaning with a non-ionic detergent solution), the surface degradation was assessed on a scale ranging from unchanged to severe change (based on the qualitative characterization presented on the standard UNE-EN 16301:2014), stereomicroscopy and colour spectrophotometry. After the 3 cycles, surfaces were additionally evaluated by measuring specular gloss, roughness and static contact angle and also by an optical and a scanning electron microscopes. Stones with similar chemical composition and similar physical properties, but with different microstructure and grain size, exhibited distinct sensitivity levels to the same stains. Despite chromatic changes were different depending on the stain applied, higher ΔE*ab were detected on the marble surfaces. Gloss only increased on the olive oil stained limestone, while it decreased for the rest of the surfaces; higher gloss changes were detected on the surfaces stained with red wine, blueberry juice, ketchup, citric acid and lime, being these last three surfaces those with the highest roughness increases. Hydrophilicity increased in both stones, regardless of the stain, being more marked on the surfaces with greater roughness increases. These different trends were related to the different dissolution levels of calcite grains considering the stain applied.