Earthen building - loadbearing walls

Appropriate methods for constructing loadbearing walls out of earthen materials include rammed earth, cob, or adobe bricks. A load-bearing wall is designed to be able to support weight from ceilings, roofs etc. External walls also have to fulfil a series of different requirements:

Thermal and physical: a wall must provide sufficient insulation against cold, heat and noise, it must be resistant to wind and draughts, should not collapse in case of fire and be resistant against weathering particularly on the outside.

Aesthetic: wall surfaces should be attractive. The surface finish can be smooth, roughened, textured or coloured. This applies primarily to the interior surface of walls.

Important: All walls made with earthen materials must be protected against the weather during the building process. When planning new buildings it is advisable to protect earthen wall constructions against the effects of water at their base, both from below and from the side. A water impervious splash protection (min. 50cm above outside surface) protects against splashing rainwater, a damp-proof course against rising damp.

Rammed earth walls

Rammed earth or Pisé wall construction can be used both for new-buildings as well as renovation work. Compared to monolithic or masonry constructions in other materials, rammed earth construction is relatively expensive. It is very often used for architectonic and aesthetic reasons rather than for functional reasons.

Rammed earth walls are constructed using formwork (typically made of steel) which is filled layer by layer with a moist earth mixture. Each layer is mechanically compacted. The formwork can typically be removed after the earth has been compressed as the earth maintains it shape. The addition of different coloured clays and earth to successive layers produces a particularly attractive surface structure which can be left without further surface treatment.

Important: Rammed earth walls should be allowed to dry out thoroughly before applying loads.

Cob walling

Cob walling is used almost exclusively for the restoration and renovation of the large heritage of rural buildings made with cob walling. The earth mixture contains a higher proportion of straw than rammed earth and contains little to no mineral substance. Cob walling does not use formwork, instead earthen clumps are layered on top of each other and the irregular sides are then ‘shaved’ with a spade to achieve an even wall surface.

Earth block walls (adobe)

Earthen blocks can be laid like another other masonry brick in coursing and bond with fully mortared joints, preferably with earthen mortar, not cement or cement-lime mortar. Earthen mortars are a mixture of earth and sand, sometimes with organic additives.

Earth blocks are used primarily for wall constructions (loadbearing and non-loadbearing) both for internal walls as well as external walls. They can be left visible as facing earthen brickwork or plastered. To make the best of the characteristics of earth, an earthen plaster should also be used applied as a single or double coat.

Important: ‘Green’ unfired bricks are susceptible to moisture and frost. They should therefore not be used for supporting walls or for external walls where they are separated only by plaster from the elements.