Impact of water repellent agent concentration on the effect of hydrophobization on building materials

It is desirable to avoid or lessen moisture-related problems in building components exposed to wind-driven rain via correct material design and/or choice. In some cases however - e.g. for historic building facades - the only possibility is to modify the hygric properties of existing materials. Hydrophobization treatment is suggested as a possible protocol, but the proper concentration of the water repellent agent to achieve the expected effect is still open to discussion. This study proposes the novel concept of a material-dependent critical agent concentration: the lowest concentration that ensures hydrophobic effectiveness on a specific material. For validation, the hygric impact of hydrophobization treatment at different agent concentrations is studied. Specifically, a balanced mixture of silanes and siloxanes is used as the agent, and eight experiments are performed on ceramic brick, lime mortar and sintered glass. Results demonstrate the existence of a material-dependent agent concentration. Only when treated above it will the hygric properties be significantly modified. Moreover, hydrophobization impacts the capillarity of a material much more than its hygroscopicity, due to the difficulty for the large molecules of water repellent agents to penetrate into fine pores. The bulk density, open porosity and pore size distribution are typically only minimally influenced.

Automated summary

The study introduces the concept of material-dependent critical agent concentration for hydrophobization treatment, which is the lowest concentration needed to ensure a hydrophobic effect on a specific material. Results show that different materials require different minimum agent concentrations to significantly modify their hygric properties.