Comparison of Latest and Innovative Silica-Based Consolidants for Volcanic Stones

Abstract

This research explores the new perspectives in conservation and protection of two macroporous tuff stones, widely employed in the architectural heritage of Campania region, characterized by highly heterogeneous rock fabric and texture and a variable mineralogical composition that represent crucial factors responsible for their weak durability. The consolidation treatments were performed with a recently and widely used suspension of nano-silica crystals in water and with a lithium silicate solution that has received up to now scarce attention as a consolidant agent. Physical investigations (open porosity, Hg porosimetry, water absorption), morphological observations (SEM analyses) and visual appearance test (colorimetric measurements), along with assessments of performance indicators such as ultrasonic pulse velocity, surface cohesion test (peeling test) and durability test (salt crystallization), were carried out to investigate the consolidation effectiveness. Overall, lithium silicate consolidant showed a better behavior in terms of superficial cohesion, a most successful strengthening action and a considerable enhancement of salt resistance.

Suitability and Sustainability of Anti-Graffiti Treatments on Natural Stone Materials

“…The pipe method, as reported in the European Standard UNI EN 16302 [24] consists in the use of a Karsten tube. This technique was useful to measure the water absorption on the surface of porous inorganic materials under low pressure, to simulate the pouring rain conditions and to estimate the efficacy of the anti-graffiti treatments [25]. The Colorimetric test (CM-2500d Konica Minolta spectrophotometer, Konica Minolta sensing Europe B.V., Milan, Italy) was performed, according to European Standard UNI EN 15886 [26], to verify the stone chromatic changes on the untreated surface and after the brushing treatment with the anti-graffiti products.…”

“…The Colorimetric test (CM-2500d Konica Minolta spectrophotometer, Konica Minolta sensing Europe B.V., Milan, Italy) was performed, according to European Standard UNI EN 15886 [26], to verify the stone chromatic changes on the untreated surface and after the brushing treatment with the anti-graffiti products. The color variation of the surface is not generally perceived by the human eye if ∆E (total color differences) is <3, while when ∆E > 5, an observer can clearly recognize different colors on the examined surface [25]. Therefore, a ∆E of 5 can be considered as the maximum threshold value generally accepted as chromatic alteration for stones that undergo coating/consolidation treatments [27].…”

SiO2 Nanoparticles as New Repairing Treatments toward the Pietraforte Sandstone in Florence Renaissance Buildings

“…The main advantage of applying these nanodispersions concerns a faster diffusion in low porous sandstone compared to the commercially available silicate products. Therefore, it follows that the consolidation efficiency will be maximum in a shorter time (about only 1 week, [20,21]), while in the case of commercial consolidating agents, the consolidation efficiency will take place on a longer time scale (≥21 days), [22,23]. This effect is mainly due to the viscosity of the solvent where the commercial consolidating reagent has been previously dissolved (the viscosity of Estel1000 is equal to 10 cP at Room Temperature, 25 • C, [6] corresponds to 100 mPa.s.…”