Microstructure and compatibility of lime putty

Understanding and reproduction of technology, manufacturing and use of pre-industrial binders issue a challenge, scientifically very alluring. This would be useful not only for the recovery of cultural heritage, but especially for the effect that the development of such scientific and technologic knowledge will have in contemporary building industry. To find one’s way through products on the market is difficult and the investigation techniques based on scientific principles used nowadays for the studies of old materials and handcraft objects aren’t able to allow us a recovery of all technology used for their production. Some traditional analytical methods were applied to define the chemical-physical and morphological parameters which best influence the technological characteristics and answer to the practicability and speed of the in situ analyses. New analytical parameters to predict the reactivity and the microstructure development of lime putty currently used in the restoration of cultural heritage has been developed. In the present research, they have been deeply examined two types of lime putty, the former containing magnesium and the latter containing calcium, which differ in microstructure and mechanical properties with the aim to establish a clear connection between their microstructure/composition and the rheological behaviour/mechanical properties. The binding mechanisms of calcium carbonate in the setting of putty-lime systems has been investigated experimentally and it has been related to the interconnected texture formed by fine CaCO3 crystallites formed during the precipitation process. The microstructure evolution of calcium carbonate is due to complex relationships between drying, shrinkage and chemical processes, that have been explained both experimentally. The starting microstructure of the lime putty seems to influence the carbonated product one, so the knowledge of the lime putties microstructure on the market could lead the choice for example, in restoration, to formulate lime mortars for compatible recoveries with old ones.