Extensive study on the efficiency of a water repellent treatment on historic natural stone, brick and mortar

In order to reduce water-related weathering of porous building materials, facades are often treated with a water repellent product. The efficacy of this treatment is generally tested in laboratory conditions, but these tests do not allow to grasp or understand the overall impact of the treatment on the hygrothermal behavior of a wall assembly. Therefore, heat-air-moisture (HAM) simulations can help to determine the treatment performance. However, water repellent layers are currently not well defined in HAM simulation programs. For this, three historic materials were extensively tested to determine the characteristics of a water repellent layer. Results show that the velocity of water absorption, 24 hour water uptake, drying speed and the sorption isotherm are, as expected, lower for treated materials. These results can be used to define water repellent layers in HAM simulations more correctly, in order to model their effect more accurately. Peer-review under the responsibility of the organizing committee of the ICMB21.