Comparison of the Degree of Consolidation of Historic Plaster Layers by Means of Lime Hydrate Nanosuspensions

Abstract

Historic masonry is usually coated with multiple plaster layers, exposed to long-term extreme loading (climatic effects, elevated moisture levels, salt crystallization and recrystallization, biological effects, etc.). As a consequence of the above negative cyclic effects, degradation processes are triggered off leading to a loss in plaster cohesion with the substrate masonry and successive falling-off of surface layers. The strengthening and rehabilitation of plasters with degraded binder components, impaired structure, insufficient adhesion of individual layers of plaster to the masonry surface, with elevated salt contents in the pore system and surface crusts represent a demanding task in terms of the stabilization of such degraded plasters and coatings. Consolidation (i.e. enhancement of mechanical characteristics) belongs to the basic objectives of the restoration of historic plasters, its principle is to return binder into the material structure, fill in existing hollow spaces, heal cracks, etc. Degraded lime plasters are strengthened with consolidating agents applied in the form of solutions, e.g. lime water, organosilicates or lime nanosuspensions, etc. The lime nanosuspension is composed of lime hydrate nanoparticles, dispersed in an alcoholic medium. Due to the deposition of calcium carbonate in the degraded material, the bonds are re-strengthened and the material consolidated. The article presents partial results of theoretical and experimental research addressing potential consolidation of historic plaster layers with lime nanosuspensions prepared by the synthesis of Ca(OH)₂, which were successively modified and enriched with other components.