Determination of hygrothermal performance of clay-sand plaster: influence of covering on sorption and water vapour permeability

Indoor finishing materials considerably influence indoor climate because of their moisture buffering ability occurring due to the sorption and diffusion properties of materials. Hygroscopic sorption properties were determined in accordance with the standard EVS-EN ISO 12571 and the principles given in the standard EVS-EN 1015-19:2005 were followed when determining water vapour permeability properties. The same specimens (thickness 2.4 cm) were used for both tests. To describe the dynamics during the first hours, the specimens were weighted at 1, 2, 3, 6, 12, 24, 48, 72 hours after changing the humidity level. Moisture uptake (kg/m2) and moisture uptake rate kg/(m2h) within the very first hours at 0-30, 30-50 and 50-80%; moisture content at RH level of 30%, 50% and 80%; points (30, 50 and 80%) at sorption curve were monitored. Six different covering materials were used: fine finishing mortar with cellulose, fine finishing mortar without cellulose, casein paint, cellulose base coat, lime paint, casein base coat, clay plaster not covered. The rate of moisture uptake was highest within the first hour after a sudden change in moisture level. Water vapour diffusion equivalent air layer thickness Sd=0.11-0.13 m was recorded.