Admixtures as modifiers of the performance of air lime mortars: an overview

The interest of air lime-based mortars is now growing in the scientific community as well as in the companies devoted to construction materials. Air lime mortars were used for centuries and many architectural monuments show this type of mortars. Modern renders and coating mortars can also be made of air lime as the main binding phase. The use of several admixtures to improve different characteristics of these mortars is now explored and discussed in the current presentation. Insights into the action mechanisms are addressed. Water-repellent agents, such as sodium oleate and calcium stearate, increase the durability of air lime mortars in the face of ageing processes. Two water retainers (hydroxypropylguar and hydroxypropylmethyl cellulose) have also been proven to increase the viscosity in the fresh mixtures and the durability of the hardened mortars. The role of a starch derivative is also discussed: the influence of the dosage of the admixture is presented. Shrinkage cracks were minimized in starch-bearing render mortars applied onto an absorbent substrate. Strength of air lime mortars can be increased upon the addition of pozzolanic additives: nanosilica and metakaolin. The combined use of these pozzolans along with superplasticizers shows an outstanding overall improvement of strength and durability of lime mortars