Water-vapour permeability of inorganic construction materials

Abstract

Water-vapour permeability (WVP) data on brick, stone, plaster and cement-based materials from some some seventy publications are reviewed and assessed. Almost all sources use standard cup-test methods or close variants. Comparisons of WVP values from different sources on similar materials confirm that reproducibility between different laboratories is poor. Some deficiencies of cup-test methods are discussed, including uncertainties arising from the use of saturated-salt humidistats and desiccants. There is some evidence that the water-vapour resistance factor decreases with increasing mean relative humidity across the test specimen; and weak evidence that the resistance factor increases with volume-fraction porosity. The contribution of liquid film flow to the measured permeability is discussed. It is concluded that (1) available data are inadequate to establish the fundamental physics of WVP; (2) vapouronly permeability data for engineering purposes should be obtained in dry-cup tests at low humidity; and (3) research studies should aim to integrate the WVP into the framework of unsaturated flow theory.