Water-vapour permeability of inorganic construction materials

Christopher Hall, Gloria J. Lo, Andrea Hamilton

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Water vapour permeability (WVP) data on brick, stone, plaster and cement-based materials from 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 evidence that the water vapour resistance factor decreases as volume-fraction porosity increases, and data support a simple porosity–tortuosity relation. Data also show that the resistance factor decreases with increasing mean relative humidity across the test specimen, with the wet-cup value consistently lower than the dry-cup values for a given material. The contribution of liquid film flow to mass transfer is discussed. It is shown how film thickness and film-flow permeability may be estimated from the water-vapour sorption isotherm; and a related regression equation is developed It is concluded that available data are inadequate to establish the fundamental physics of WVP; vapour-only permeability data for engineering purposes should be obtained in dry-cup tests at low humidity; and research studies should aim to integrate the WVP into the framework of unsaturated flow theory.
Original languageEnglish
Article number39
Number of pages20
JournalMaterials and Structures
Issue number2
Publication statusPublished - 26 Feb 2024


  • water vapour permeability
  • water vapour diffusivity
  • water vapour resistance factor
  • cup test
  • humidity
  • porosity
  • film flow
  • sorption isotherm
  • Schirmer equation


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