Last edited 08 Oct 2018

Clay in construction

Clay is a finely-grained natural rock or soil material that, along with other materials such as stone and wood, has been used as for construction for thousands of years. It is composed of one or more clay minerals (such as kaolinites or smectites), sometimes with small quantities of quartz, metal oxides and organic matter. Clay is formed very slowly as a result of the weathering and erosion of rocks containing the mineral group known as feldspar.

Due to the particle size (typically, a grain size of less than 4 micrometres (μm)), and water content, clays have a high plasticity until they are dried or fired, at which point they become hard and brittle.

Classified as a fine soil, clay has the following characteristics:

  • Dry lumps can be broken but not powdered between fingers.
  • It is smooth to the touch.
  • It shrinks on drying which usually leaves cracks.
  • Its particles have intermediate to high plasticity.
  • It has a sand or gravel content of less than 35%.
  • Its compactness is soft.
  • Its structure can be fissured, intact, homogeneous, inter-stratified, or weathered.

Clay is used around the world as a construction material, most commonly baked into brick or roof tiles. The relative ease with which clay can be extracted from the ground and processed – e.g. by adding water to change its shape, or increasing its strength by adding straw, sand, etc. – means that it can be considered 'sustainable'. In addition, it provides relatively good thermal insulation and thermal mass.

Clay is also an important ingredient in composite materials such as adobe, cob, rammed earth, wattle and daub, clay plaster, clay mortar, ceramics, and so on.

Clay has good robustness, stability and durability. It is fire-resistant and capable of withstanding seismic activity, giving it a potential lifespan of 100 years or more.

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