SUSTAINABILITY IN THE maintenance and protection of architectural surfaces: innovative Water-repellent pozzolana-lime mortars

Laura Falchi1, Urs Müller2, Patrick Fontana3, Francesca C. Izzo1, Eleonora Balliana1 , Guido Biscontin1, Elisabetta Zendri1

1 Ca’ Foscari University of Venice, Department of Environmental Sciences, Informatics and Statistics, Via Torino 155/B, 30172 Venice – Italy – laura.falchi@unive.it, elizen@unive.it

2 Swedish Cement and Concrete Research Institute, Brinellgatan 4, SE-504 62 Borås, Sweden

3 BAM, Federal Institute for Materials Research and Testing, Division Building Materials, Unter den Eichen 87, 12205 Berlin, Germany

Abstract

Water-repellent renders were studied in order to evaluate their suitability for restoration applications. Water repellent admixtures, such as powdered siloxane-based products and metal soaps (zinc and calcium stearates), were mixed with a pozzolana-lime binder similar to historical binders with hydraulic properties. The chemical-physical and structural properties, the effectiveness and the durability of the water-repellent mortars in different environmental conditions were studied. The influence of the water repellent admixtures was evaluated by FT-IR analyses, by testing the mechanical properties and the behaviour in presence of water. The durability of the water-repellent mortars was evaluated after the exposure to artificial weathering (UV-light and water) and to immersion/drying cycles in saturated sodium sulphate solution. The nature of the water-repellent admixtures influenced both the hydration reactions and the chemical-physical properties of the mortars resulting in different resistance to the weathering and to salt crystallization.

Key-words: Water-repellent admixtures, artificial weathering, salt crystallization, restoration mortars