Sticky rice - nanolime as a consolidation treatment for lime mortars

For almost 1500 years, many ancient Chinese mortars have remained unaltered despite exposure to atmospheric agents. The main reason for this long-term durability is the addition of sticky rice water to the standard mortar ingredients (lime and sand) following traditional recipes. In recent years, these mortars have been methodically studied leading to the conclusion that amylopectin, a polysaccharide in the sticky rice, plays a crucial role in regulating calcite crystals growth, creating a denser microstructure and providing the mortar with hydrophobic properties which contributed to their survival. In recent decades, nanolime products based on Ca(OH)2 nanoparticles suspended in alcohol or hydro-alcoholic medium, have been extensively used for the consolidation of calcareous substrates mainly due to their chemical affinity and absence of side-effects. Nanolime products have resulted in successful superficial consolidations. However, in-depth consolidation still needs to be achieved, and research needs to focus on ways to attain this objective. This study aimed to test a novel approach consisting of applying a pre-treatment of sticky rice and subsequently the nanolime. The resulting consolidation was evaluated by measuring changes of superficial cohesion, porosity, contact angle, drilling resistance, water absorption by capillarity, drying rate and aesthetic properties. The durability of the treatments was investigated by exposing samples to accelerated weathering. Results showed that the use of sticky rice in combination with nanolime yields a higher degree of consolidation increasing drilling resistance and delivering hydrophobic properties although prolonged exposure to high temperature and moisture can compromise treatment durability.