Greening earthen plasters: a study on bio-sourced polymers as stabilizers

Earthen material is a common construction material that has been used for centuries. Today, it is estimated that around 50% of the world's population lives in buildings made from earthen material. The widespread availability of this material combined with its low embodied energy makes it an attractive option for sustainable construction. However, the use of stabilizers (such as cement or acrylic resins) to improve its durability and mechanical performance can have a high environmental impact, reduce its recyclability and compromise its hygrothermal properties. In the past, earthen material was stabilized using fibers, agricultural waste and biopolymers, but little research has been conducted on their properties and suitability for other techniques due to the challenges of standardizing such systems. At this moment, an alternative, as compromise, is represented by bio-sourced polymers which allow to reduce carbon footprint and CO2 emissions. In this work, earthen materials for plasters have been prepared in the lab and stabilised by using two different types of bio-sourced polymers (alkyd emulsion and urethane alkyd dispersion). Experimental tests for measuring mechanical, heat and mass transfer properties have been carried out on six different mix-designs. A comparison between results obtained for earthen materials as received and stabilised by using bio-sourced polymers have been reported. No particular improvements have been noted in system treated with alkyd emulsion, while those fabricated by using urethane alkyd dispersion show similar thermal conductivity values but relevant enhancements in mechanical properties (about three times the value measured for as received samples) and water resistance (lower capillary rise and lower capillary coefficient).