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The influence of storing slaked lime under water for extended periods of time (i.e., aging) on Ca(OH) 2 crystal morphology, texture, and carbonation evolution of various lime mortars has been studied by the combined use of X-ray diffractometry, phenolphthalein tests, porosity measurements, electron microscopy, and ultrasonic wave propagation analyses. Mortars prepared using traditional aged lime putties (up to 14 years storage under water) show rapid, extensive carbonation, resulting in porosity reduction and ultrasonic speed increase. The aged hydrated lime mortar carbonation reaction (i.e., Ca(OH) 2 ؉ CO 2 ‫؍‬ CaCO 3 ؉ H 2 O) follows a complex diffusive path, resulting in periodic calcite precipitation as Liesegang rings. In this case, binder:aggregate ratios >1:4 result in crack development. Nonaged commercial hydrated lime mortars show slower carbonation and need a higher binder:aggregate ratio (1:3). The carbonation of nonaged lime mortars follows a normal diffusion-limited continuous path progressing from the mortar sample surface toward the core. Differences between aged and nonaged lime mortar carbonation evolution are explained considering Ca(OH) 2 crystal shape changes (from prisms to platelike crystals) and size reduction that occurs on aging of lime putty. Implications of these results on historic building conservation using traditional lime mortars are discussed.

Liesegang patterns, generally rings, bands, spheres or spirals, form in far-fromequilibrium systems in nature and in the laboratory by self-organized periodic precipitation of sparingly soluble phases following a nonlinear reaction-diffusion process. Although Liesegang patterns have been known for more than hundred years, there is still disagreement as to the mechanisms underlying this phenomenon. Most studies have focused on Liesegang pattern formation in gels, quantitative studies of quasiperiodic patterns in non-conventional porous media (e.g. construction materials) being rare. Here, we report the development of 'revert' three-dimensional Liesegang patterns (i.e. concentric ellipsoids) in traditional lime mortars undergoing carbonation. Portlandite (Ca(OH) 2 ) in a quartz (SiO 2 ) sand aggregate, transforms into calcite (Ca(CO) 3 ) in contact with atmospheric CO 2 , resulting in banded cementation of the lime mortar. Surprisingly, well-developed Liesegang patterns only occur in mortars prepared using 'aged' lime putty, kept under excess water for years, following an ancient Roman recipe to improve slaked lime quality; the carbonation of these mortars being faster than in pattern-less ones. The smaller Ca(OH) 2 particle size in the long-term-aged putty enhances dissolution and increases the ion-concentration product, while creating a higher volume of pores with r < 0.1 µm. These small pores can sustain very high supersaturation ratios with respect to CaCO 3 , resulting in higher nucleation rates, a crucial fact for pattern development previously neglected. These results may have strong implications for the understanding of Liesegang patterns, as well as for the conservation of architectural heritage.