Procedure to determine the impact of the surface film resistance on the hygric properties of composite clay/fibre plasters

The experimental determination of dynamic mass transfer properties of porous materials such as eco-efficient clay plasters is greatly influenced by the convective conditions at the surface of the material during the test. The measurement of the intrinsic vapour permeability of highly porous materials has shown to present wide discrepancies when the surface film resistance is not known. Therefore, a proper assessment of the hygric properties of clay plasters requires the determination of such resistance to vapour flow. An adapted experimental procedure was used to determine intrinsic water vapour permeability taking into account the influence of the surface film resistance. The moisture buffering test was used to measure dynamic exchange behaviour. The results gave evidence on the thickness of the active layer in the material and the impact of surface resistance on the exchange behaviour. A 1D mass transfer model was used to verify the validity of corrected vapour permeability by the surface film resistance and discuss its nature and influence on dynamic results.