Towards understanding rain infiltration in historic brickwork

Historic masonry walls are typically afflicted with uncertainties and defects which might induce significant rain water infiltrations. Insight in these moisture transport mechanisms in brickwork is important because the moisture content of brickwork is the predominant parameter for damage functions for frost, mold, and corrosion, and also affects heat flux. Given the increased focus on low-energy retrofits, interior insulation is becoming more popular. However, this typically decreases the drying potential of the wall and might consequently induce even more moisture-related pathologies. The insulation causes the exterior surface of the brickwork to be saturated more often, and this renders it possible for a runoff water film to develop during heavy rainfall. Although it is well known that this water film can penetrate through defects in the brickwork, the amount of water that penetrates remains a big question mark. Consequently, this important transport mechanism is typically omitted in hygrothermal simulations of (historical) brickwork. To obtain quantitative information, a series of laboratory tests is conducted. In a test setup a runoff film is applied in combination with a range of air pressure differences on a surface with different types of deficiencies representing imperfections in the facade. In this first phase, as an abstraction of the real saturated masonry construction a PMMA surface was used. The applied runoff film is imposed precisely and the water infiltration rate through the deficiencies is measured gravimetrically. Finally, the laboratory results are analyzed and preliminary linear relations between pressure and infiltration rate are found.

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