Influence of substrate pore size distribution, poultice type, and application technique on the desalination of medium-porous stones

This paper studies the influence of poultice type and application techniques on the desalination efficiency of two limestone substrates having similar porosities (22–25%) but different pore size distributions: microporous Bateig Novelda and macro porous Tosca Rocafort stones. Three poultice types are compared: pure sepiolite (fine porous), sepiolite and aggregate (medium porous), and pure cellulose powder (coarse porous). Four application techniques are studied: (i) direct application on the stone, (ii) pre-wetting before poultice application, (iii) Japanese paper before application, and (iv) pre-wetting + Japanese paper before application. Samples were taken from poultices on the one hand, and from substrates at different depths on the other hand. Their content in soluble salts was estimated by ionic conductivity measurements. After three application runs, the best result for both substrates is achieved with the combined application of coarse- and fine-porous poultices (FPs) (desalination depth: 4.5/6 cm for macro/micro-porous substrates). The FP is also able to extract salts properly, but the desalination depth achieved is less important (3 cm). A direct poultice application without pre-wetting nor Japanese paper is to be preferred for both stone types.