Traditional gypsum renders in the Paris area: focus on a particular typology

This study aims to characterize the “Parisian” traditional gypsum renders in order to understand its former fabrication process. A large sampling campaign covering the historical region of Paris and all building typologies from the sixteenth century to the early twentieth century was conducted. This paper presents the results obtained on the most typical gypsum render typology, which we identified as “Parisian.” Cross-sections of the renders were first observed with the naked eye and then under the microscope to characterize the number, thickness, and grain sizes of their layers. X-ray diffraction analysis and mercury intrusion porosimetry were performed on each render layer and the proportion of each crystalline phase was estimated using the Rietveld method. Calcite and quartz contents are low and vary from building to building and even between two layers in a single render. Gypsum appears to be the main component as only calcined gypsum was used to prepare the renders. The different layers were made from a single coarse calcined gypsum powder, sieved at different grain sizes, and mixed with water without any addition of lime or aggregates.