Development of a gypsum-based grout for the stabilisation of gypsum-based plasters

Abstract

Research on injection grouting for the stabilisation of delaminated wall paintings and historic plasters mostly focuses on grouts based on aerial or hydraulic lime and on earthen-based grouting. Materials for the stabilisation of delaminated gypsum-based plasters have never been fully studied, even if gypsum has been used as a constituent material of wall paintings since ancient times. Grout mixtures developed during this research were specifically designed for the stabilisation of the 11th-century gypsum-based wall paintings in the Ateni Sioni church in Georgia. Due to the gypsum sensitivity to water, it was important to reduce the water content of the grout; this was achieved by partially substituting water with an alternative liquid, i.e. ethanol. The grout mixture design involved laboratory testing to assess the working properties and some performance characteristics of the grouts. In addition to the regular tests, grouts were injected into replicas simulating the challenging horizontal delamination present in the vaults of the church. The research proposes gypsum as the binder for a grout together with the use of a water-reduced dispersion medium, aiming to stabilise delaminated gypsum-based plasters.