Moisture buffering capacity of clay-based plasters
Abstract
The European ISOBIO project aims to develop new bio-based insulation panels and coatings showing low embodied energy and high hygrothermal efficiency. After optimization of composites, typical walls for new building and retrofitting will be designed, targeting energy saving and indoor comfort. These multi-layers walls will include indoor plaster that will highly contribute to indoor comfort. This paper investigates the moisture buffering capacity of clay-based plasters. Three formulations developed within the ISOBIO Project, are investigated. These formulations are clay-based and include hemp powder and pumice. After weight stability, drying shrinkage is measured and thermal properties are evaluated for densities ranging from about 1250 to 1425 kg/m3. Thermal conductivities are closed to values commonly measured on earthen materials. The measurement of Moisture Buffer Value (MBV) is performed following two type of protocols. After stabilization, specimens are exposed to daily cyclic variation of ambient relative humidity. For each formulation, three thicknesses of specimens are considered. The lower thickness, about 1.3 centimeters, is representative of the plaster in-use. So, the MBV is representative of in-use behavior. The two higher thicknesses are used with the aim to study the effect of thickness on MBV and to identify MBV representative of the material’s one. Consequences of protocol modification in MBV measurement is evaluated and discussed. The three tested plasters are classified as good hygric regulators. A slight discrepancy appears between the three formulations (about 6.5 % for the in-use thickness) showing the limited incidence of formulation changes.
