The Role of Application Techniques for High Performance Traditional Renders

Traditional renders based on lime had an aesthetic as well as a protective role for the historic masonry. They were applied in layers in order to ensure good adhesion and cohesion with the substrate but also in order to be functional. The technology of each layer was different in relation to the maximum grain size of the aggregates and the binder/aggregate ratio. Main requirements were the high water vapor permeability, the low water retention in order to avoid salt formation and the capacity of water absorption by capillarity of each layer should increase outwards. As moisture has a detrimental role in the thermal behavior of materials, an effort has been made to record the effect of layering in energy properties. Lime-based renders were tested in relation to their hybrid properties when different application techniques were followed. Two-layer renders with different technological characteristics in each layer were produced. Their behavior, in various deterioration mechanisms such as capillarity, external water uptake (measured by karsten tubes) and water vapor permeability was monitored. It seems that low porosity and adequate permeability is achieved in two-layer renders while the thermal conductivity was effective.