Production of eco-efficient earth-based plasters: Influence of composition on physical performance and bio-susceptibility

Abstract

An experimental campaign was developed to evaluate the properties of earth plastering mortars, not only at the level of workability and physic-mechanical performance but also their susceptibility for biological colonization. A ready-mixed earth mortar and several other mortars formulated with a raw clayish earth were produced. The influence of partial replacement of fine sand by a phase change material (PCM) and the addition of low amounts of oat fibres and hydrated air lime were assessed. The experimental campaign shows that the PCM completely changes the mortar workability, with a decrease on wet density. The addition of PCM and fibres decreases the bulk density and, consequently, increases the porosity of the mortars. The presence of PCM, fibres and air lime decreases the thermal conductivity. Earth mortars are susceptible to mould 2 development, and the fibres or PCM seem to intensify their bio-susceptibility. A low addition of air lime increases pH and inhibits fungal growth though decreasing the mechanical properties. Mortars with PCM, fibres and air lime present a higher surface roughness in comparison to other mortars, including the ready-mixed earth mortar with fibres. Surface roughness was found to be an important factor influencing the level of colonization.

Earth-based mortars for repair and protection of rammed earth walls. Stabilization with mineral binders and fibers

“…Emphasis should also be drawn to the decrease of thermal conductivity when the percentage of binder is increased, with and without fibers (with the exception of the earth mortar with 10% HL). The study performed by Santos et al (2017), with low content of air lime used to stabilize an ilitic earthen plaster, supports the same results: when a binder is added, thermal conductivity decreases. This may find justification on dry density.…”

“…It is known that the use of earth as a building material may have problems when having direct contact with water and even the testing procedures to assess that type of performance need to be carefully defined (Gomes et al, 2016a). The susceptibility for biological development may be another question to deal with and, at least for an ilitic earth, stabilization with a low content of air lime, although decreasing the mechanical strength, contributed to decrease the biological development of earth-based plasters (Santos et al, 2017). Old masons say that air limeearth mortars were used, by mixing air lime with local grinded earth, particularly to obtain less expensive renders.…”

Biological susceptibility of earth plasters: The influence of relative humidity on fungal growth

“…The samples which were dried in the relative humidity below 25% for 2 days showed smaller extent of mould than the samples dried in higher relative humidity. This result proves that moisture is one of the most relevant factors infl uencing the occurrence of microorganisms [2]. If we compare placing the samples after drying in 5 desiccators with different relative humidity ranging from 33% to 100%, the highest values of fungal growth rate were noted in 100% RH according to our expectation.…”

“…It is known for the ability of absorbing and desorbing water vapour, thus regulating the relative humidity of indoor environment which leads to better indoor air quality and comfort and health of the occupants. People also appreciate the natural colouring and texture of the earth materials [2].…”

“…The presence of fungi can lead to respiratory problems or allergies of the occupants of the buildings. Apart from external conditions, the intrinsic properties, such as po-M. SOKOLOVÁ, P. RYPAROVÁ rosity, pH and chemical composition, also affect the bio-susceptibility [2]. The addition of natural fi bres may also contribute to microorganism proliferation [3].…”