The impact of the exterior painted thin-layer render’s water vapour and liquid water permeability on the moisture state of the wall insulating system

The paper aims at the determination of the possible limits of vapour resistance and liquid water permeability alteration in the case of the exterior painted thin-layer render finish of the building walls from outside insulated with the mineral wool slabs when exploited in the area of cold and humid climate that could guarantee a normal moisture state of the wall insulating system. The moisture testing of the insulating system’s fragments was carried out in the climatic chamber, where the climatic parameters were modelled on the basis of the climatic typical of Lithuania. Thin-layer render was coated with acrylic paints. When the thickness of the paint coating on thin-layer render was increased from 0.08 mm to 0.24 mm, the liquid water absorption coefficient decreased by 59% and vapour resistance increased by 43%. It has also been determined that in the double-layer system paint coating – thin-layer render condensation moisture will be accumulated when the thickness of the air layer s_d equivalent to the material’s water vapour permeability is higher than 0.6 m. Rain will have an impact on the wall’s moisture state, when the liquid water absorption coefficient w of the double-layer system paint coating – thin-layer render is higher than 0.025 kg/(m² h^0.5). The micro-lens discovered in the areas of moisture accumulation by the thermographic analysis should be considered as the rudiments of the defect formation in the exterior insulating system.