Clay and indoor air – what studies show

How clay absorbs moisture

The decisive factor is the clay content. Many clay plasters contain the clay mineral montmorillonite. It consists of very fine, layered crystals with a large surface area: one gram amounts to up to around 800 m². Water molecules attach themselves to this surface.

This allows clay plaster to even out fluctuations in humidity: when humidity rises, for example during cooking or showering, it absorbs water vapour and releases it again later. How much a clay plaster can absorb is classified into classes WS I to WS III according to DIN 18947. The thicker the plaster layer and the larger the surface, the more moisture it can absorb.

Study on ozone (University of Texas, 2017)

Two clay coatings were installed in occupied homes for six months and tested in the laboratory every two months. The clay surfaces removed ozone from the indoor air. Only a small amount of by-products was formed, and it decreased significantly after about two months.

Source: Darling, E.; Corsi, R. L.: Field-to-laboratory analysis of clay wall coatings as passive removal materials for ozone in buildings. Indoor Air 27 (2017), pp. 658–669

Classification

The study tested clay coatings from the USA, not the products in our range. The results apply to the substances and conditions examined. They do not show that clay plaster removes pollutants from indoor air in general. Regular ventilation remains important in rooms with clay plaster too.

Evidence for our clay plasters

For conluto clay plasters, manufacturer declarations state that they meet the requirements on harmful substances for the German state Quality Seal for Sustainable Buildings (QNG). You will find these declarations and the environmental product declarations of the Dachverband Lehm (German clay building association) on the respective product pages.

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