Unlike hydraulic limes (NHL) and cements, which harden by reacting with water, air lime (lime putty) needs air to solidify. It is the leading binder of entire millennia of architecture, from ancient Greece to the Italian Renaissance.
The process begins with firing very pure limestone rocks (CaCO3) at 900 degrees C to obtain quicklime (CaO). This is then slaked with abundant water, becoming calcium hydroxide in suspension (the lime putty). The supreme quality of the render derives from the maturing time of the putty in dedicated tanks: ageing from 6 to 48 months, the lime particles arrange themselves into hexagonal structures, ensuring unequalled plasticity, workability and tenacity.
In restoration, the low mechanical strength of air lime is actually its greatest asset. Forming a very porous and elastic render (low elastic modulus), it accommodates the thermal and structural settling of old masonry without creating the typical cobweb cracks of cement materials. Furthermore, it acts as a sacrificial render: it allows the salts contained in old walls to crystallise on its surface rather than destroy the stone or brick behind it.
Standards
European and international references applicable.
Physical properties
Usage environment
Since it dries slowly through evaporation and CO2 absorption, aerial lime plaster must not be applied outdoors in winter or near-zero temperatures, lest it crack from frost before carbonation completes.