Replicating Medieval Wall Painting Plaster using the Hot-mix Technique

This paper describes attempts to replicate medieval plaster using hot-mixing, where quicklime, aggregate, and water are combined in a single exothermic process. The experimental study aimed to reproduce the structural characteristics of medieval plaster while making sample materials for conservation trials, rendering them more relevant and comparable with the medieval materials on which treatments take place. For wall painting conservation, similar capillarity and permeability are particularly important for trials focusing on consolidation, desalination, and cleaning. These characteristics are greatly influenced by the materials, working protocol, and curing conditions used in the replication process. Replicated plaster and plaster sampled from Gothic wall paintings were analysed to provide data regarding porosity, type of lime, aggregates, and binder/aggregate ratio using thin-section analyses, X-ray diffraction, porosity measurements, and mercury intrusion porosimetry. The comparative study showed a close match between one of the two recreated mortars and the original plaster.