Microstructural Changes of Lime Putty during Aging

Abstract

The microstructural development of lime putty is widely recognized and commonly associated with an increase in quality. Many heritage institutions encourage the systematic application of lime putties in conservation; however, all the issues associated with age are not fully understood. Changes occur during storage underwater, which traditionally took place in pits to prevent carbonation. The properties of mortars, plasters, and decorative finishes formed from lime putties are intimately linked to manufacturing parameters such as storage time. The hydration of calcium oxide was investigated using an environmental scanning electron microscope with particular attention to the nucleation of calcium hydroxide crystals on the surface of calcium oxide. Crystal modifications were monitored. The results obtained confirm and quantify the influence of slaking time in the microstructure of lime putties that is also reflected in the current referred special characteristics of the mortars produced with them, such as greater plasticity, water retention, and reactivity of mortars. The results also emphasize that the most significant microstructural changes of the lime putties start to consolidate after 8 months of slaking and appear to continue to develop, even though at a slower rate, until at least 5 years.