Traditional organic additives improve lime mortars: New old materials for restoration and building natural stone fabrics

Portland cement has low chemical and physical affinity for traditional building materials. This hinders the restoration of historical buildings and modern rustic architecture where natural stone is used. Lime mortars used in construction since c.12,000 B.C. were recovered, and attempts were made to enhance their properties. Various additives were selected on the basis of their properties and historical use. These include polysaccharides (opuntia, also known as nopal used either as a powder or as mucilage), proteins (animal glue and casein) and fatty acids (olive oil). Six types of lime mortar were formulated and characterized. Compressive strength, water-resistance, carbonation speed, porosity, texture and mineral composition were measured. We propose new lime mortars with added value, i.e. increased mechanical properties and water-resistance, different carbonation speeds, and different textures. They are all compatible with traditional building materials, so they can be used in the restoration of architectural heritage and modern architecture where natural stone is used.