Hygric behavior of hydrophobized brick and mortar samples

Moisture that penetrates into porous building materials is a major reason for their deterioration and the sub-sequent failure of the whole structure. Water repellency treatment could prevent serious damages to materials and components. Hydrophobization is a method with a long tradition for protecting buildings from wind-driven- rain-induced moisture absorption. Nonetheless, it remains an ambiguous practice. To understand the nature of water repellency it is important to examine how hydrophobization works, how the existing products differ from one another, and how the hygric response of the substrate changes after treatment. The aim of this article is to characterize the impact of water repellent agents on the properties of building materials mostly used in old facades: clay brick and lime mortar. The resulting open porosity and pore size distribution, determined with vacuum saturation and mercury intrusion testing respectively, reveal only minimal change in the overall pore structure after impregnation. Our findings also show that hydrophobic treatment is nearly impermeable to liquid water, by evaluating the samples with capillary absorption tests, but still permeable to water vapour, by testing the samples with cup tests. Moreover, the water impermeability grows after exposure to water. In addition, the water repellent agent ap-pears to spread progressively in the material for a long time after the hydrophobic treatment, yielding high final impregnation depths. These findings confirm that water repellent agents successfully hydrophobize the tested materials, with a water-tight but vapour-open hydrophobic layer that goes deep into the material, without notably changing its pore size distribution though.