Hygric properties of Cement-Lime Plasters with Incorporated Lightweight Mineral Admixture

Cement-lime plasters are among the most often applied materials for surface finishing of interior and exterior surfaces of buildings. In order to improve their properties, especially the thermal insulation performance, common silica filler is often replaced with lightweight filler. The main positive effect of the thermal insulating plaster is reflected primarily in winter, preventing freezing of water in the masonry porous structure. In this paper, novel cement-lime plasters with lightweight aggregate are studied. In plasters composition, silica sand was replaced with perlite. The replacement ratio was 25 %, 50 %, 75 %, and 100 % by volume. The effect of the sand substitution on plasters structural characteristics, such as bulk density, matrix density, and total porosity, was tested. As one of the plasters functional properties is to protect the masonry from the water penetration, i.e., from the moisture related damage, and at the same time the moisture from the structure must be efficiently drained, determination of their moisture transport parameters is of the particular importance. In this respect, the water vapour transmission rate in the developed materials was characterized by water vapour permeability, water vapour diffusion coefficient, and water vapour resistance factor. For the description of the liquid moisture transport in the studied plasters, a 1-D vertical water uptake experiment was performed. Based on this experiment, moisture profiles that characterize moisture distribution along the sample length at the specific time of water suction were determined. Using inverse analysis of moisture profiles, the moisture dependent moisture diffusivity was calculated. Since the admixed lightweight filler increased the moisture diffusivity of the developed plasters, their samples were in the second set of tests provided with a hydrophobic coating based on silicone oil. This improvement helped to reduce the moisture diffusivity of plasters to the value of the reference mixture. In summary, presented experimental analysis of hydrophobised lightweight plasters proved their increased porosity and reduced moisture diffusivity, which can improve plasters thermal performance and prolong the durability of both the plasters themselves and the masonry they cover. (paper)