Performance of clay-straw plasters containing natural additives
Earth constructions need to be protected from severe weather conditions in order to reduce their maintenance requirements. Constructive solutions such as overhanging elements play an important role to this intend, but plasters are also crucial. Traditionally, lime and clay plasters are considered to be the most adequate for such structures due to their water vapour permeability and suitable hygrothermal behaviour. The present paper show preliminary results of an ongoing research on clay plasters that may be used to protect earth walls. Barley straw shredded to different particle sizes and natural additives i.e. casein, linseed oil and alginate are added in different proportions to the clay plasters. The hygrothermal performance and durability of the different specimens is evaluated both in laboratory and on-site tests. Water vapour permeability and thermal conductivity are measured in order to evaluate the hygrothermal behaviour of the samples. Erosion and water uptake are also monitored with the aim to investigate the applicability and durability of the different formulations. Fibre size seem to be a driven factor in dimensional stability of the clay plaster, which is reduced in samples with higher fibre sizes. Among the treatments analysed, linseed oil in bulk application yield the best results as significantly increases the resistance to water erosion, reducing the penetration depth about a 60% with respect to the untreated clay plaster. Moreover, it seems to reduce the thermal conductivity of the material. Further work should be done in order to optimise the formulations and confirm these findings.