The influence of moisture content on the thermal conductivity of external thermal mortars

The growing European interest on building sustainability has driven the establishment of the 2012/27/UE Directive. Mortars with thermal conductivity lower than 0.2 W/m·K (thermal mortars) can have an important role in the energy efficiency of buildings. The thermal conductivity is a fundamental parameter to characterize the hygrothermal performance of mortars. Nevertheless, its measurement is complex due to its large dependency on several factors and its dynamic behaviour. In the present paper, an experimental campaign is carried out to evaluate the influence of the moisture content on the thermal conductivity of 17 thermal mortars. Moreover, correlations between thermal conductivity analytically estimated from standards and experimentally measured are assessed. The results showed that the thermal conductivity is significantly dependent on the moisture content. However, most of the building standards use fixed conductivity values for normalized conditions. Therefore the discussion of relevant influence factors on thermal conductivity of thermal mortars can help designers and professionals to evaluate the hygrothermal performance of in-service buildings facades with thermal mortars, when subjected to real exposure conditions.