The benefits of clay in modern buildings
The benefits of clay in modern buildings
by ROCKCOTE Natural Materials specialist, Tony Thorogood
From the ziggurats of ancient Babylon to the teahouses of 16th century Japan, clay has been used in building for centuries. As one of the most sustainable and healthy building materials on the planet, clay has enormous potential for making our buildings healthier and reducing the impacts of construction on the planet.
Across the world designers and architects are ‘rediscovering’ this incredibly versatile material while modern day artisans draw are finding new ways to interpret this finish for modern buildings.
So why aren’t more of us using clay in our homes and offices? Clay still struggles somewhat with the perception that a clay finish means brown dirt walls and therefore is completely at odds with the modern building.
The truth is that clay is a highly versatile product and in the hands of a skilled artisan can be used to achieve a full range of finishes from a lustrous polished finish to an undulating traditional rustic finish. Beyond homes and offices, clay also performs exceptionally well in commercial environments such as hotels, schools and restaurants or cafes.
Unlike most common internal decorative or paint finishes that offer limited finishing options, clay can be finished in a multitude of ways and can look completely different with the slightest change in application technique. The range of finishes achievable can be anything from like a 500 year old mud hut to the most beautiful modern polished finish imaginable.
Compared with painted surfaces, the slightly open texture of clay means it reflects and refracts light differently providing a softer, more even and more natural light. The availability of natural oxides means clay can now be tinted to a wide range of colours.
Don Cameron, curator of the award-winning Hotel Hotel in Canberra (see Hotel Hotel gallery) that features earthen render throughout the 68 consciously designed rooms, said it helped achieve an “unadorned approach” to the rooms: “I was looking for a render that had a raw, textural quality that was rough and didn’t conceal the natural ingredients.”
Springbrook home owner, Suzy Worrall said the clay lifted the mood of what was previously a damp and dark home: "I like to walk down the hallway and touch the clay walls, feeling the texture and temperature. It has an effect on people because it has so much more character than paint." (Read more about Suzy's renovation project in our gallery A little piece of hinterland heaven.)
General health benefits
Being surrounded by clay walls gives occupants a sense of coinhabiting with the earth – it brings you back to nature. The coating is breathing, actively controlling humidity and cleaning the air, therefore helping us live better, breathe better and feel healthier and happier. Clay does not offgas like many internal finishes and releases no toxins into the indoor air.
“Negative ions are odourless, tasteless, and invisible molecules that we inhale in abundance in certain environments. (1)”. Negative ions have been linked with an assortment of benefits to mood and mental clarity. Fresh country air is filled with negative ions; computers, televisions and synthetic plastics on the other hand, emit a positive charge. When it comes into contact with water, clay releases negatively charged particles into the air which is why people who live or work in spaces finished in clay often report feeling calmer.
Moisture management and breathability
Clay has remarkable moisture management properties and the “ability to relinquish any absorbed moisture as quickly as it was taken on” (2).
Using Natural Finishes provides an excellent description of this process:
“When the water evaporates from the body of the clay, the platelets are pulled closely to one another, hence the characteristic nature of clays to shrink when they dry. Beneficial to anyone working and sculpting with clay however is that the platelets will remain in the same shape that they have been moulded into, even when they dry. …it can be indefinitely re-wetted and reworked, ensuring it can be infinitely recycled as a building materials.” (3)
This effective management of moisture means clay will not support the growth of mould and assists in the maintenance of a more consistent indoor temperature. Water absorbent finishes such as clay plasters can ‘contribute to ameliorating the relative humidity fluctuation caused by ventilation and human activities in houses’ (4). By controlling the moisture in the air, rooms finished with clay generally maintain a humidity in the ideal range for comfort of 40-70%. As little as a 20mm later of clay plaster can “substantially moderate the daily cycle of indoor relative humidity” (5).
Caution must be exercised when adding hemp, straw, horse hair or other materials that change the chemical composition of the clay - as a consequence mould could grow in the right conditions, particularly in areas with high humidity.
Clay is an excellent insulator. The thicker the clay, the better the insulation. Clay applied over plasterboard at 1.5cm thickness provides some insulation (certainly a lot more than paint) but at 6-10mm thickness produces optimum insulating results. As a guide, a straw bale home would usually include 35mm of clay which helps generate and improve insulation. If extreme temperatures and high humidity is an issue, I recommend applying 4-6mm clay to ensure the space is cooler in summer and warmer in winter.
With reports that people in the developed world are spending up to 90% of their time indoors, the need to actively pursue interior finishes that help to improve indoor air quality has never been more important. Clay achieves this, and so much more along with unique aesthetics delivered by its inherent natural beauty.
Tony Thorogood is ROCKCOTE’s natural materials specialist and a passionate advocate for creating spaces that nurture human health and tread gently on the planet. This article first appeared in ROCKCOTE's online magazine, The Natural Artisan.
Image credit: The University of Jordan
2. Weismann, Adam & Bryce, Katy: Using Natural Finishes, Green Books Ltd 2008, p.144.
3. Weismann, Adam & Bryce, Katy: Using Natural Finishes, Green Books Ltd 2008, p.147.