Earthen Building Materials  
Rammed Earth
Clay straw
Light earth
Earth filling
Earth mortar
Earth blocks
Earth panels

Earthen building materials are available loose or formed into building products and are typically made from unfired clay with or without additives. As a result, unlike fired or cured products, they become hard as they dryout and become softer again when they take up moisture. This process can be controlled through the addition of mineral or vegetable additives to reduce shrinkage and/or cracking, to improve tensile, compression or abrasion properties or to increase water-resistance. Light additives improve thermal insulation properties.


Rammed earth

Rammed earth is based on naturally damp and crumbly earth which is compressed into a form and left to dry and harden. With densities ranging from 1700 to 2200 kg/m³ it is the ‘heaviest’ form of earthen building.

Rammed earth structures can therefore be loadbearing. The earth is filled into a form and compressed in layers similar to conventional in-situ concrete. Alternatively large rammed earth blocks can be pre-cast in moulds and then assembled on site much like brickwork on a larger scale.

Monolithic constructions with rammed earth have until very recently been very scarce in Germany, but a series of exceptionally attractive projects such as the Chapel of Atonement in Berlin signal its spectacular ‘resurrection’.

In countries such as Australia or the USA, the addition of cement to rammed earth is normal practice.

Cob-walling or the building of ‘weller’-constructions with mud and mud-manure is also a traditional way of building. The addition of straw differentiates it from rammed earth and makes it a ‘lighter’ construction with a density of betwen 1500 and 1800 kg/m³. It can also be made into loadbearing structures.

In contrast to rammed earth ‘weller’-construction is typically not enclosed in formwork. The mud-straw mixture is piled using a fork in layers of up to 80 cm until the full height of the construction has been reached. The wall surface is smoothed and a drying period between layers is necessary.

‘Weller’-construction is used today principally for the repair of such existing structures.

Clay straw

Clay straw or fibrous clays are mixtures of prepared clay and organic fibres, primarily straw. After application and drying they have a density of between 1200 and 1700 kg/m³.

Clay straw is applied whilst still wet and malleable and is used today particularly for renovation work for example as daub or fill material in timber-framed constructions.

Clay straw is available pre-mixed and can also be formed into bricks or panels.

Light earth

Light earth describes prepared clay mixed with organic or mineral additives to a pulpous or fluid consistency. Organic additives include straw or wood chips, mineral additives include thermally expanded materials such as foamed clay or shale. As a result the density can vary considerably from 400 to 1200 kg/m³. The addition of light additives improves the thermal insulation considerably.

Due to the high levels of light additives light earth is not suitable for bearing loads but is very often used in combination with loadbearing structures in particular timber or stud frames as a fill material. It is also ideally-suited for use in renovation work.

Light earth is available ready-mixed and also formed into bricks or panels with a variety of densities. Light earth is often named after its dominant additive.

Earth fill material

Earth and clay together with mineral or organic additives can be used as loose fill material for horizontal cavities, for instance in floors and ceilings. Earths and clays whose cohesion properties are unsuitable for other applications can be used here.

Such fill materials, after application and drying have a density of less than 1200 kg/m³.

Earth mortars

Earth mortars are earth and clay thinned with fine-grain and / or fine-fibrous additives. Depending upon their usage they are known as earth masonry mortar, sprayed earth mortar or earth plaster mortars or rendering.

Earth masonry mortars are used for bricklaying with earth bricks as well as with synthetic, fired or stone bricks. They are typically thinned with sand.

Sprayed earth mortars are used for filling out timber frame panels, for the manufacture of inner leaf coatings, interior walls or as filling in floor cavities. It is thinned with mineral or organic additives that are suitable for use with a mixer and spray-pistol. Much like some plasters, it is applied from a spray-pistol in as many layers as are necessary to fill the cavity or reach the required thickness.

Earth plaster mortars or rendering are used for plastering internal walls and ceilings and in some cases exterior walls if these are protected from direct rain. Sand, straw or other organic fibres are typical additives. The fibres serve to bind the plaster and reduce cracking as the material dries. Due to its moisture regulating properties, earthen plasters are particularly suited for use indoors.

All earth plasters are available in a wide variety of densities and with different additives or colours as well as in different quantities and packaging forms. As earth mortars do not cure they can be delivered in large quantities and can be stored under normal conditions over long periods of time until required.

Earth blocks

Earth blocks and bricks can be manufactured from several of the aforementioned raw earthen building products. To ensure material and form stability, clays and earth with so-called thin cohesion should be used.

Depending upon the density of the bricks, they are laid according to traditional bricklaying using earth masonry mortar to form load-bearing structures.

The forming of the raw material into bricks or blocks produces a homogenous formed building element. Typical manufacturing methods include hand-pressing, forms or extrusion machines as are used in the manufacture of bricks.

Bricks made using the extrusion process for bricks but not fired are known as ‘green’ or unfired bricks. Due to the high degree of compression and fine mineral structure they have a high density but as they are not fired they are susceptible to moisture uptake. They are therefore used principally in interior walls or floors as fill material. Their high mass is particularly good as a thermal store and helps regulate room temperature by slowing down the differences in internal to external temperature.

Earth-bricks are available in a variety of densities and sizes as well as additives.

Clay panels

Clay panels are manufactured using various different methods from several of the aforementioned raw earthen materials. They are typically mixed with ground clay.

Clay panels are an ecologically sound addition to the palette of dry-lining products. They are available in a variety of sizes much like conventional boarding products. Clay panels with a thickness of 50 mm are not self-supporting and require a supporting construction. Thinner panels or boards employ a carrier such as reed matting. They can be used in all typical dry-lining situations: as wall or ceiling cladding, with a supporting structure for non-loadbearing separating walls, as plaster boarding or as formwork.

Clay panels with a thickness of more than 50 mm (typical thicknesses range from 80 - 125 mm) are self-supporting and require no supporting structure. They find increasing use in dry construction or as infill in walls, floors and ceilings.