Improving hygrothermal properties of clay

The requirement to reduce operational energy use in the built environment has driven a rise in the level of building envelope airtightness. An unintentional consequence of this can be a reduction in the indoor environment quality with respect to hygrothermal comfort. Some aspects of this may be addressed through correctly commissioned active ventilation systems. However, there is also a need to consider the passive role that building materials have in maximising the quality of the indoor environment.

There has been growing interest in the use of exposed clay surfaces for the passive regulation of indoor temperature and humidity levels. This is largely due to the exposed thermal mass and hygroscopic properties that help buffer the temperature and relative humidity of the internal environment. There is also scope for the inclusion of mineral and organic aggregates to help improve these hygrothermal properties.

This paper presents results from preliminary testing on a range of novel clay coatings, which incorporate different mineral and organic aggregate contents. Two novel mixes were prepared with an enhanced level of mineral and organic aggregate exchange. Both mixes showed a reduction in thermal conductivity compared to control clay mixes. The moisture buffering of the plaster was improved by the increased organic aggregate content while no significant change was observed for the mineral aggregates. The results of this paper will inform future developments of clay plasters, which will support the development of airtight buildings with improved indoor environment quality.