Do interface resistances matter in historic masonries? -Analysis based on Xray tomography and heat, air and moisture modelling

For hygrothermal simulations it is often advised to homogenize masonry wall constructions into a 1D solid brick construction. This saves computational time, but it may lead to an underestimation of moisture related risks. Some literature states that the impact of mortar is negligible, but no specific attention was paid to historic masonries, which often have high absorptive mortars (e.g. lime) and/or bricks. Hence, this study investigates the impact of the interface resistance between brick and mortar, in relation to the properties of the adjacent materials during absorption as well as under real climate conditions. As expected the impact of interface resistances is more pronounced during an absorption test compared to under real climate conditions. Nevertheless, due to the interface resistance, increased frost risks do arise in a number of cases subjected to real climate conditions. The results are found to be highly dependent of the climate, the sequence of rain and frost events, and the properties of the adjacent materials. In conclusion, one can state that there can be an increased risk of frost damage due to the effect of interface resistances in historic masonries. However, deriving generic guidelines on the impact of these effects remains a challenge due to a high dependency on climate and material parameters