CLAY: A SIMPLE MATERIAL WITH MULTIPLE PROPERTIES
Clay-based building materials for resistant, durable, eco-friendly and healthy homes
History and use
Clay is a natural, sustainable, and simple material, with multiple properties. It has been used since ancient times for pottery, writing boards, art objects, musical objects, and especially construction works. Prehistoric people were the first to discover the useful properties of clay. Some of the earliest pottery fragments were found in Honshu, Japan, and date to around 14,000 BC.
Clay, as a defining ingredient in the composition of loam, is one of the oldest building materials on earth, among other natural ancient geological materials, such as stone, and organic materials such as wood. Between half and two-thirds of the world's population, both in traditional and developed societies, live or work in buildings made of clay, often burned in bricks or ceramic blocks, as an essential part of its load-bearing structure.
As a primary ingredient in many natural construction techniques, clay is used to create structural elements as adobe, cob, cordwood, rammed earth, and building elements or materials such as wattle and daub, clay plaster, clay floors, and clay paints. Clay was used as a mortar in brick baskets and stone walls, where it is protected from water.
Physical and chemical properties
Chemically, clay is a natural rock or a fine-grained natural soil (less than 0.002 mm particle size), which combines one or more clay minerals with possible traces of quartz (SiO2), metal oxides (Al2O3, MgO, etc.), and organic matter. Geological clay deposits are mostly composed of phyllosilicate minerals that contain varying amounts of water trapped in the mineral structure.
Clays are plastic due to the size and geometry of the particles, as well as the water content, and become hard, brittle, and non-plastic when dried or burned. Depending on the content of the soil in which it is found, clay can appear in various colors such as white, gray, brown, or deep orange to red.
Being a natural material with very good physical and mechanical properties, we use it as an interior finish in NIDUS Homes. Also, for special applications that require high thermal inertia, we use it building rammed earth walls.
Rammed earth
It is an ancient clay-based construction technique that can be used to make foundations, walls, and floors by successively compacting a mixture of soil, clay, lime, and gravel, resulting in a compact construction element, resistant and durable over time.
The above-mentioned materials are placed in a formwork together with a stabilizer (cement usually) and compacted successively around a support structure, up to 50% by volume. After removing the formwork, the wall can be plastered with clay or left in its compacted form by applying a protective varnish. In the pictures above, we compacted the mixture of compounds into layers of different colors, for a special design. A water coil or electrical resistance can be inserted into the wall, in order to capitalize on the high thermal mass of the wall and thus keep the interior warm or chill, even though the HVAC systems are turned off.
The rammed earth construction elements are very strong and durable over time if they are executed correctly and can reach up to 20MPa resistance at compressive force. A significant benefit of this material is the very high thermal inertia, which helps to passively regulate day/night temperature variations and indoor humidity in the range of 40-60% if the interior walls are not further finished with plasters that prevent the wall to dry or "breathe".
Dry Clay
It consists of a mixture of clay, sand, water, and a fibrous organic material such as sawdust, straw, or hemp as reinforcement. The mixture is poured in various forms and dried naturally in the sun or at low temperatures, not being burned in the oven, such as brick or terracotta. Dry clay is available on the market in the form of boards, reinforced with hemp mesh or other similar organic materials.
The boards are very easy to install. Ther are mounted on the walls by screwing and due to the fact that it is naturally dried and not baked, it contributes significantly to the regulation of humidity and temperature. It is a modular, high-performant, and acoustic solution. In terms of sound insulation, a 22mm clay board is equivalent to 3 gypsum boards of 12.5mm.
Why Clay
Clay is a natural material available in abundance, it is very versatile, being used for thousands of years in various industries. Recently, clay-based building materials (and we are not referring to bricks or ceramic blocks) are beginning to get more and more public attention, being considered a solution in reducing the buildings' impact on the environment.
Clay-based building materials are non-toxic, have a very low carbon footprint (as long as it is not burned), contribute significantly to the regulation of humidity and indoor air quality, are resistant to fire and pests, contribute passively to maintain a constant temperature due to the high thermal mass and is also a good sound insulator.
The only disadvantage is that each clay-based construction system requires intensive and sometimes specialized work. But balancing all the benefits for the environment and people, we believe that the effort pays off.