Water vapour sorption in twelve mineral and bio-based building materials measured by the Dynamic Dewpoint Isotherm (DDI) method

Water vapour sorption is essential to understand the hygric behaviour of building materials. This study introduces an experimental method for quantifying vapour sorption dynamics. We applied the automated, non‑equilibrium Dynamic Dewpoint Isotherm (DDI) method to generate detailed ad- and desorption isotherms for 12 building materials. An overall sorption response surface (SRS; moisture storage as function of water activity or relative humidity) was generated for each material by completing a cyclic run of 14 ad- and desorption isotherms. DDI-measured moisture storage capacity at apparent equilibrium agreed well with an equilibrium method. The wideness (magnitude of hysteresis) and shape (surface and pore-network controlled) of the SRS varied greatly in regard to material composition, porosity, and density. This was used to group the materials in regard to level of moisture dynamics with high-porosity and bio-based materials showing the highest level of sorption dynamics. The DDI-SRS concept seems useful to illustrate and quantify dynamic moisture storage behaviour of building materials and elements under changing relative humidity.