Abstract
Plasters have covered wide surface areas of buildings since antiquity, with a main purpose of indoor protection of the substrate on which they are applied. When no longer functional, they might require substitution with solutions that can combine compatibility with the substrate with the current need to mitigate building emissions. Indeed, plasters can contribute to lowering buildings’ energy demands while improving indoor air quality and the comfort of buildings’ users, as plasters can be used as passive regulators of relative humidity (RH). Hence, this study presents the relative-humidity-dependent properties of different plastering mortars based on clay, air lime, and natural hydraulic lime, and plastering finishing pastes based on gypsum and gypsum–air lime, in all cases tested using small size specimens. A cement-based plaster is also analysed for comparison. The clay-based plaster was the most promising material for RH passive regulation, and could be applied to repair and replace plasters in different types of buildings. Pastes based on air lime–gypsum could be applied as finishing layers, specifically on traditional porous walls. The sorption behaviour of cement plaster appeared interesting; however, its water vapour permeability was as expected, found to be the lowest, discouraging its application on historic walls.
Highlights
Plasters are “a mix of one or more binders, sand, water and sometimes additives” [1]that have been used for covering interior walls and ceilings since antiquity
The old plasters were commonly based on clayey earth, air lime, and gypsum [2,3]
The passive regulation of relative humidity (RH) performed by plasters [7,8,9] has been largely discussed during the present century, since the interest in human health [10], indoor air quality (IAQ) [11], and perceived air quality [12] has spread, together with the aim of adapting historical buildings to climate change [13]
Summary
Plasters are “a mix of one or more binders, sand, water and sometimes additives” [1]that have been used for covering interior walls and ceilings since antiquity. Traditional plasters cover a large surface of historical buildings and represent themselves as part of the built heritage. During the 20th century, many interventions oriented to the repair and conservation of old buildings were carried out with complete substitution of original mortars with new binder-based ones [5], which frequently contributed to accelerating the degradation process of the built heritage. The intervention in historical buildings must consider compatibility criteria; i.e., physical, chemical, and mechanical compatibility [6], and should aim to improve indoor air quality and decrease the energy demand of buildings. The optimization of passive RH regulation represents an opportunity for improving indoor comfort while reducing the need for HVAC systems, improving energy efficiency in historic buildings [14,15] and lowering their environmental impact and operational costs, which are fundamental to mitigate climate change [16] and reach a climate-neutral Europe by 2050 [17]
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