A return to clean, green building materials Replacing lime mortar with cement for the repair and maintenance of historic buildings during the past two centuries has led to irreversible damage. An EU initiative set out to design new, sustainable and environment friendly lime-based mortars. Industrial Technologies © Shutterstock Restorers and manufacturers now appreciate the need to use lime in the design of sustainable, compatible and durable repair mortars. In recent years, industrial mortar production has led to ready-to-use mortar that lacks the quality of its traditionally prepared alternative. There is a clear requirement to use sustainable building materials and to implement methods that lead to less pollution, carbon emissions and energy consumption. To address this issue, the EU-funded NATURALIME (Naturally durable: Developing and testing the resilience of innovative natural admixtures for lime-based conservation mortars) project set out to design lime mortar to be used as repair material for historic buildings. Project partners examined and used natural admixtures composed of lime and vegetable and animal derivatives to modify certain characteristics of mortar. To this effect, they investigated dry hydrated lime, natural hydraulic lime and lime putty. The NATURALIME team studied mortar prepared with the hemp plant and its shiv (inner woody part of the stem). Results reveal that mixes of hemp shiv with natural hydraulic lime perform better than those made with aerial limes in the form of dry hydrated powder or putty. Hemp-lime mixes also appear to be durable in Mediterranean, semi-arid and tropical climates. Researchers also studied mixes made with lime and organic additives, particularly natural polysaccharides from seaweed. They found that adding these polysaccharides to the lime paste increases the plasticity of the fresh mix in a manner that depends on the mixing process, time and temperature. Overall, findings show that natural hydraulic lime is best used with hemp shiv. NATURALIME successfully demonstrated the consequences of natural and sustainable admixtures on repair mortars. Through this project, the monument and historical heritage of Europe should benefit for years to come. Keywords Lime mortar, repair mortars, NATURALIME, hemp shiv
