Earth Plasters: The Influence of Clay Mineralogy in the Plasters’ Properties

Abstract

Earth-based mortars have been used all over the world since ancient times in an extensive range of building types from vernacular architecture to monuments.Plastering is one of the most common contemporary applications of earth-based mortars used for earthen-building conservation or modern architecture. Raw earth is a very diverse natural material, and clay minerals play a key role in plaster properties being responsible for their setting process and providing the capacity of balancing the indoor hygrometric conditions of buildings. This capacity offers significant benefits to energy savings delivering comfort and health of inhabitants and also contributes to building conservation. For this study, three mortars were produced with different clayish earths to assess the influence of clay mineralogy. Mortars characterization confirmed that clay mineralogy drives important plaster properties, such as vapour adsorption and drying shrinkage, while also having a significant influence on mechanical strength, dry abrasion, and thermal conductivity. Within the studied mortars, illitic clayish earth stands outs as more adequate for earth-based plasters, showing balanced properties, namely linear drying shrinkage, mechanical strength, dry abrasion, and water vapour adsorption.

Traditional and Modern Plasters for Built Heritage: Suitability and Contribution for Passive Relative Humidity Regulation

“…The five specimens for each plaster were then sealed on their edges and their bases with aluminum tape (Figure 3c), ensuring only one exchanging surface was exposed. They were used to perform adsorption/desorption according to a simplified version [38] of DIN 18947 [25]. After preconditioning in a climatic chamber (FITOCLIMA 700EDTU) at 50 ± 5% RH and 23 ± 5 • C until reaching a constant mass, the specimens were weighed and the starting mass, m 0 , was determined.…”

“…-values from the literature[33][34][35][36][37][38][39][40][41][42][43][44], due to the lack of results for permeability or resistance factor in some cases, were calculated using δa of 19.50 × 10 −11 (kg/(m•Pa•s)); -value above the range; -value below the range; **-range from the literature for cement refers to the wet-cup test method.…”

Mortars, plasters and pigments—research questions and sampling criteria

“…- Centauro et al (2017) carried out a series of ageing tests adding linseed oil, brown sugar and cow's milk; - Nunes et al (2018) investigated the microstructure and composition of lime and metakaolin pastes with linseed oil added and aged for 68 months; - Zendri et al (2004) reproduced "cocciopesto" mortars, in order to investigate the reactions responsible for conferring hydraulic properties to these products; -Nežerka et al ( 2014) compared the pozzolanic activity of metakaolin and crushed bricks; -Işikdaǧ and Topçu (2013) compared the mechanical strength of mortars, including tile powder, crushed tile, lime and granulate blast furnace slag; -According to ancient recipes, Salavessa et al (2013) compared the compressive and flexural strength of plasters prepared with either waste marble or limestone dust; - Vejmelková et al (2012b) investigated the mechanical and fracture-mechanical properties, hydric parameters, durability characteristics and thermal properties of several lime-pozzolana composites, using a particular clay shale that is available in the Czech Republic that may have been the natural substitute of volcanic pozzolanas (absent in Central Europe); - Yang et al (2009) and Yang et al (2016) reproduced the mechanism of solidification of sticky rice mortar; - Ventolà et al (2011) tested different types of non-hydraulic lime mortars, adding animal glue, casein, nopal and olive oil to develop new compatible products for repairs; - Lima et al (2020) investigated the effects of clay mineralogy on drying behaviour, pore size distribution, mechanical strength, vapour adsorption, desorption capacity, water capillary absorption, linear dry shrinkage, cracking and thermal conductivity. They also verified the greater suitability of illitic clayish earths compared with montmorillonitic or kaolinitic ones.…”

Vernacular Caramel´s Adobe Masonry Dwellings – Material Characterization

“…The capillarity test was performed based on the EN 15801 (2009) but caution was taken to avoid the loss of mass during the test. Based on Lima et al (2019) and to reduce particle loss, the base and lateral surfaces of specimens were enveloped in a water vapor permeable synthetic fabric, with small openings, invisible to the open eye , and with low water absorption. To avoid direct handling of the specimens and prevent the degradation during the weighing, the specimens were placed inside metallic net baskets.…”