benefits of Natural clay plasters in retrofit and new-build
Bridport Cohousing
by Maria Krupa
Last week I visited the Bridport Cohousing scheme to take part in a clay plastering course lead by the School of Natural Building (SNaB). During the five days there we plastered the interior of the Common House building – the future community hub of the cohousing community.
Barefoot was involved in the design of the common house up to the planning stage. The technical design and building has been taken on by the local studio Common Practice and self-built with the residents, local carpenters and workshop students.
The common house is built using local, natural materials throughout – it's a timber frame building with infill straw bale walls, foundations made of recycled tires, external lime plasters and internal clay plasters. Clay plastering has been one of the last stages of the self build process.
Here's the plastering process:
(1) (2) application of first 'key' coat of the clay plaster
(3) second – 'body' coat
(4) a bath full of 'slip' coat
(5) (6) finish coat – ready for drying and painting with clay paint
(7) lime plastering in progress in the future kitchen – it's all about round door reveals
(8) cohousing site in full bloom
It was great to get some hands-on experience with this material as we specify it often. Clay plasters can be applied onto a range of internal wall and ceiling surfaces, including strawbale, hemp, timber fibre board or standard gypsum plasterboard (onto appropriate primer). We use it in new-build and retrofit projects.
Here's a non-exhaustive list of the advantages of the clay plasters:
It can create beautiful finish! Clay can be mixed with minerals or natural pigments to be through-coloured
Natural material
Non-toxic (low VOCs emissions, and don't require synthetic additives)
Low embodied carbon – it's dried not fired (as opposed to lime plasters which are)
Can be sourced locally (sometimes from the project site itself)
Easy to repair if damaged
Biodegradable
Fully reusable - can be taken off and reapplied on another wall
Helps manage and buffer humidity in the room (clay is hygroscopic – it adsorbs moisture when the humidity in the room is high and releases it back to the air when the humidity falls.
Helps with acoustics (dampens the sound)
Long–lasting (expected lifespan 60 years)
Further reading
https://www.backtoearth.co.uk/news/in-praise-of-clay-plaster/
https://bridportcohousing.org.uk/courses/
https://commonpractice.io/COMMON-HOUSE
https://bridportcohousing.org.uk/the-common-house/
Case studies
https://www.dezeen.com/2021/03/14/natural-clay-wall-finishes-interiors-dezeen-lookbook/