Eco-efficient Plasters for Increased Indoor Air Quality and Comfort

Abstract

Indoor walls and ceilings are often coated with plasters. Due to the large surface in contact with indoor air, the plasters can passively contribute to moisture regulation and pollutant removal. The work presented intends to better understand this contribution, while enhancing, when possible, the plasters formulations for the purpose. The first step was to analyze the hygroscopic response of traditional and modern binder-based plasters. To do so, a first study was run to quantify the relative humidity fluctuations indoor. Then, the methods fitting the most the real indoor microclimates were selected for testing. The campaign was run along with bibliographic research, to match laboratory results with those ones present in literature. The compatibility with the preexisting materials and products and the eco-efficiency of the plasters are two parameters that were kept in mind during the work. According to that, clay and gypsum based plastering mortars were selected as the most promising materials. Both, in fact, are present in traditional architecture, besides being suitable solutions for new construction, and have low embodied energy. However, while the clay-based plasters showed a high hygroscopic behavior, the gypsum-based ones showed a lower one. For this reason, the latter was modified through the addition of biomass and the clay-based plasters were kept as a benchmark along the study. The plant selected for the scope is Acacia dealbata, an invasive species that plays a role in the spread of wood fires in Portugal. The biowaste addition was aimed at enhancing the moisture buffering of gypsum-based plasters without jeopardizing other properties or their carbon footprint. Good results were obtained, increasing the moisture buffering ability of the gypsum plaster up to double, even if still lower than the clay-based ones. The ozone reactivity and primary and secondary emission rates (VOCs) of the innovative gypsum-based plaster and the clay-based ones were also analyzed. The ozone removal ability of the gypsum-based plaster was improved by the biomass addition, the primary emissions increased a little, but the secondary ones were very low. Clay-based plasters overall confirmed their low emissions and ozone removal activity.