Stabilised vs Un-Stabilised Rammed Earth

As the sustainability and health of buildings have come into the spotlight earth building has seen a resurgence in popularity, but there has also been an increasing trend of adding cement to rammed earth buildings. Now there is confusion about what true rammed earth is and what has been marketed as “stabilised rammed earth”, but what is actually rammed concrete. Cement was seen as modern and easy to use, and clay was seen as mud or dirt. A poorly formulated mixture could easily be supplemented with cement to make it bind and become a shortcut that allowed anyone who could mix concrete to start building “stabilised rammed earth”. Earth building is characterised by the use of clay to bind together rock, sand, silt and other raw and natural materials. It is the clay that makes a building an earth building. It is the clay that is responsible for almost all of the positive qualities that earth buildings are known for.

Soon people realised that clay and small amounts of cement interfered with each other and cancelled each other out, so less clay and more cement were used. Eventually, clay was left out entirely, grey cement was replaced with more expensive white cement and synthetic oxides were added to recolour the walls and make it look like rammed earth. What was once a minimally processed earth material had been turned into cement, sand and gravel – the exact same materials used for concrete. Furthermore, due to the thickness of the walls, a “stabilised rammed earth” wall uses more cement than would be used for a typical concrete construction, yet people and companies are still marketing is as an eco-friendly green construction method.

Cement is possibly the most damaging material on Earth. If cement was a country it would be the third-largest carbon dioxide emitter in the world. The article Concrete: The most destructive material on Earth details just how damaging the use of cement and concrete has been for our planet.

Cement undoubtedly increases the compressive strength (the amount of force required before the earth or concrete fails when it is compressed) and reduces the potential for erosion, but in almost every other way it has a massively negative effect on the building.

Cement is:

  • Concrete is hard, rough and cold to touch, while clay is soft, warm and textured
  • Concrete is unable to regulate humidity properly
  • Concrete doesn’t store and radiate heat as well as clay-based earth
  • Concrete requires chemical additives to stop water from entering the walls
  • Concrete doesn’t work as well with other natural materials like timber, lime and plant-based products
  • Cement is incredibly energy-intensive and polluting to produce
  • Rammed concrete has visible construction joints
  • The cement in the walls often leaches onto the walls totally ruining the appearance

Clay is:

  • Abundant and easily found all over the world and can often be dug up on the building site
  • Non-toxic and doesn’t require any additives
  • Has almost no environmental impact
  • Is either free or very low cost
  • Requires little or no maintenance and can easily be repaired with no visible sign
  • Regulates temperature and humidity better than any other building material
  • Is strong and durable and buildings have been proven to last for centuries

The difference between using clay or cement is so great that the two methods cannot be considered to be the same. When deciding to build a rammed earth home the choice between true rammed earth and rammed concrete is one of the most important decisions. One is healthy, sustainable, natural, low-energy and beautiful, and the other is simply a concrete structure with none of those properties.