Healthy interiors by using clay walls


A big shout out to the Swansea based Down to Earth Project, which is engaging vulnerable people in every aspect of constructing stunning sustainable buildings, visibly transforming their lives.

From the mammoth effort of peeling wooden poles, through the tricky whittling of straw bale stakes, to the messy plastering of walls with mud: these are just some of the many jobs that vulnerable members of the community get involved in, bringing purpose, fun, nature and fulfilment into their lives.

Round pole timber framing, straw bale insulation and a beautiful wild flower and turf roof form the building structure; clay plasters that have been both dug up on site and sourced from Clayworks, finish the walls.

Health and wellbeing.

We have nearly five years of clinical research to back up our approach to construction as improving the mental health and well-being of the people we work with, explained Mark McKenna, co-founder and director of the project.


Photo courtesy of Down to Earth.

Moisture control

Vapour permeability was a key reason for selecting clay plasters, said Mark.

The walls are designed to be fully breathable and use natural insulations so options were limited. We chose clay as it is much more accessible and safe to work with for our groups than other options, and has a warmth and aesthetic unlike any other finish.

 Clay plasters have a thirst for moisture. Its most prized characteristic is its ability to readily attract and take up moisture from the atmosphere and retain this moisture within its pore structure. Earth plasters are therefore hydrophilic (water loving) and hygropscopic (can safely hold onto this moisture).

Furthermore, as it incorporates this moisture into its structure, it causes the clay molecules to expand, blocking the further passage of moisture through its structure. This forms a water resistant barrier. This self-sealing ability can prevent moisture from wicking into the wall substrate beneath, while still allowing moisture to move back out.

Clay is hence one of the most ‘breathable’ building materials.

An earth plaster’s ability to attract and hold water makes it highly suitable for use on straw bale walls and against wood. Because earth plasters are more hydrophilic than straw and wood, they will readily take up any excess moisture in both materials and then release them into the air (as long as the air is drier than the clay plaster). Cement, which is less hydrophilic than most soft building materials, would cause the reverse action to take place, with the cement loading moisture onto the wood or wall substrate.

Library and archives design

Clay plasters’ ability to help regulate moisture in the internal atmosphere also makes it extremely useful for use in libraries, museums and other archiving or storage buildings, where humidity needs to be regulated.