Aging of Lime Putty
This work was carried out at the Getty Conservation Institute and first published in "Calcium Hydroxide Crystal Evolution upon Aging of Lime Putty," Journal of the American Ceramic Society, 81, (11) 3032-3034, 1998.
"Aging of lime putty, by storing slaked lime under excess water for extended periods of time, has been recognized for centuries as a means to improve the quality of hydrated lime as a binder in lime-based mortars and plasters. However, there is limited, and at times contradictory, evidence about the effect of extended exposure of portlandite Ca(OH)2 to water. Our data from X-ray diffraction, nitrogen adsorption, and scanning electron microscopy studies indicate that portlandite crystals undergo both an important size reduction and a significant morphological change, developing submicrometer, platelike crystals upon aging. A model for portlandite evolution is proposed and discussed, based upon (a) differences in solubility between (0001) basal pinacoid faces, and  prism faces, and (b) heterogeneous secondary nucleation of nanometer-scale platelike portlandite crystals."
In subsequent studies at the University of Granada, another effect on mortars formulated with aged lime putty was found to be the induction of a novel pattern of carbonation or Liesegang pattern, published in "Liesegang pattern development in carbonating traditional lime mortars," Proceedings of the Royal Society, No. A. 458, 2261 (2002) by C. Rodriguez-Navarro, O. Cazalla, K. Elert, and E. Sebastian Pardo. Carbonation of aged putty, as qualitatively estimated by phenolphthalein staining, revealed that the carbonation of aged lime putties follows a complex discontinuous, diffusive path which results in periodic calcite precipitation as rings, as opposed to what is normally expected from carbonation; i.e., a normal diffusion limited continuous path that progresses from the mortar surface into the interior. The aged putty also carbonated faster than the putty from dry hydrate, as indicated by XRD. The significance and further details of the behavior of aged putty were published in "Lime Mortars for the Conservation of Historic Buildings," Studies in Conservation, 47, 62-75 (2002) by Kerstin Elert, Carlos Rodriguez-Navarro, Eduardo Sebastian Pardo, Eric Hansen, and Olga Cazalla.
Last updated: October 2007