Resumen: Lime based mortars used for the repair and renovation of old lime renders have important functions in historic buildings, such as the protection of the masonry and aesthetics of the surfaces. Hence, they have a significant contribution to the durability of the walls, which often are structural elements.
Cracking and loss of adherence are two of the most severe defects for renders, as they drastically affect their functional capacity. Cracking is related to shrinkage, elastic characteristics, and kinetics of the gain of strength as well as to water transport properties of the render. Most of these aspects are governed by the porous structure of the mortar, which is a function of the composition of the mix and application issues. Loss of adherence is related to the compatibility of the render with the substrate, concerning mechanical, thermal and hygric aspects. Loss of cohesion, due to leakage of the binder, freeze-thaw, salts crystallization or other causes, results in significant damage, difficult to repair. The appearance of stains either by pollutants deposition or by biocolonization is also a concern related to durability of renders.
In the present paper the degradation mechanisms leading to cracking, loss of adhesion or cohesion and stains formation are analysed based on literature, and a review of assessment test methods are carried out. Finally, the need for test improvement in this area is highlighted.