Influence of application method and number of applications of nanolime on the effectiveness of the Doulting limestone treatments

Abstract

Over the last two decades, nanolime has been recognized as a promising consolidation approach to consolidate historic calcareous substrates due to its compatibility, durability and fast carbonation. The effectiveness of nanolime products has been widely proven for superficial consolidation treatments, especially in historic wall-paintings. However, its consolidation mechanism in highly porous substrates, such as in the case of limestones or lime mortars, still needs to be fully understood. This paper aims to study the influence of application method and number of applications on the effectiveness of nanolime treatments, which has never been targeted until now. In this experimental work, the Ca(OH) 2 nanoparticles were freshly synthetized by anion exchange resins and applied in historic Doulting limestone samples, extracted from a capital from the Cathedral of Wells (Somerset, UK). In order to study the influence of application method on the effectiveness of treatments, samples were treated by: (1) brush; (2) spray; and (3) capillary absorption. Additionally, to study the influence of the number of applications on the consolidation effectiveness, these three application methods were applied by: (1) 1 application; (2) 5 applications; (3) 10 applications. The consolidation effectiveness of the resulting nanolime treatments was studied by assessing changes in porosity, superficial and internal stone’s density, superficial cohesion, water absorption by capillarity and aesthetic properties. Results showed that repeated applications (i.e. 10 applications) of a low concentrated nanolime (i.e. 5\xa0g/L) by spray and brush can increase the superficial cohesion, mechanical properties and density of the stone at the surface. Additionally, results suggest that the application method does not significantly affect the consolidation effectiveness of nanolime treatment, contrary to what was commonly believed. Results also show that a single application treatment of low concentrated nanolime (i.e. 5\xa0g/L) does not significantly provide noticeable consolidation effectiveness regardless of the application method, also contrary to what was commonly believed. These results suggest that for a noticeable consolidation treatment with low concentrated nanolime the application must consist of several applications (>\u200910). This could have a high impact on the Built Heritage conservation community that commonly use nanolime in conservation activities.