Making Rammed Earth

The process of making rammed earth starts with the selection of the raw material which is a subsoil made of; gravel, sand, silt and clay. Normally this mix is found from a naturally occurring local source, of which there are many. The mix should contain a good distribution of particle sizes so when it is being compacted it will form a dense matrix that will make the finished wall hard like stone.

Rammed Earth Mixing

The mix is prepared by adding some cement, color if desired and sprayed with a modest amount of water while being mixed. The addition of cement creates stabilized rammed earth (SRE), this basically means that the clay which acts as a binder in the material will not be able to reabsorb water and has therefore been stabilized, creating a stronger and more durable wall. The material is mixed together until it is like the consistency of cookie dough, not too wet and not to dry, which makes it optimal for compaction. There are a variety of ways to mix the rammed earth material. The most common way used today is by using a Bobcat or similar machine but can be mixed by hand or other devices such as a volumetric mixer.

Ramming Earth

The damp mix is then placed inside of a form that is typically made of wood or metal in 6 to 8” lifts (layers) and compacted either manually or mechanically until solid. The manual tool is usually a pole with a plate or block on the end made of wood or metal and the mechanical tool is a pneumatic rammer that runs off an air compressor. Once compacted, another layer of earth is placed inside the forms and rammed. This process is repeated until the desired height is reached. The forms are usually removed the next day and a new wall that looks ancient now exists.