Clay corrugation
The clay corrugation is a historical solid clay technique, which in rural areas, especially in Thuringia , Saxony and Saxony-Anhalt, was the main type of construction for erecting wall structures until the second half of the 19th century . Today, several 10,000 rural residential and farm buildings using the clay corrugation technique have been preserved.
Despite the name similarity are Weller and Weller woods not in cob used, but serve as part of the widespread Lehmwickeltechniken for filling wooden beams as well as compartments in the framework construction .
The starting material combines both techniques. Lehmweller is a mixture of straw and loam that is mixed with a damp cloth, then manually or by machine and then soaked (bricked) at least overnight. In the clay corrugation building, it was immediately piled up with a pitchfork to form a massive wall, usually 50–120 cm thick. On a large scale, the mixture can be mixed homogeneously using a garden tiller or compost turner and then kneaded by driving over it with the tractor. It used to be pounded by oxen.
Due to the proportion of straw, clay corrugated walls up to a height of 50–90 cm were dimensionally stable even without formwork when damp. After about 5 days the next layer was applied and after 10-14 days the uneven side surfaces could be evenly cut off with a sharply ground spade. Unplastered clay corrugated walls can be recognized by the cut straws in the wall surface.
In order to obtain a more even wall surface, the corrugated walls were probably also partially covered. The transition to rammed earth construction is therefore fluid.
Since a massive straw clay wall has to dry for a long time, these thick walls in unheated buildings can only be built between March and August so that they can dry out in the warm season without the damp wall freezing in winter. Due to its pronounced capillarity , the clay enables the solid wall to dry out. Bundled damp straw dries extremely slowly. In the case of light clay mixtures with a low proportion of clay, part of the straw should therefore be replaced by light mineral aggregates to improve drying .
Due to the increased moisture levels over weeks, mold can form on the wall surface , especially in warm temperatures and poor ventilation. With the help of small fans, a slight movement of air can be achieved. The resulting evaporation cooling and the removal of the moist air limit the growth of mold. Since clay and straw are not suitable substrates, the development of mold is limited to the surface and it can be easily brushed off after the wall has dried out. If the ventilation of the wall cannot be ensured during the drying phase, the wall can be provided with clay plaster immediately after completion. Mold can be easily removed from the plaster surface, especially if the drying cracks that form are regularly closed by smoothing the surface with a trowel .
During the drying phase, the wall settles by up to 15 cm per storey, so that window and door lintels have to be decoupled from the wall or installed in a movable manner and the wall plaster should only be applied after it is almost completely dry.
If the clay wall is protected against renewed moisture after drying, it can be centuries old. As with all earth building methods, earth preserves organic materials such as straw and wood thanks to its moisture-balancing properties.
The volume weight of the dry wall is around 1700–1850 kg / m³ in traditional construction. In the case of non-load-bearing walls, in particular, it can be reduced even further by increasing the proportion of straw up to 1300 kg / m³ and using light aggregates. Traditional rammed by contrast often reach 2000-2200 kg / m³.
Literature, sources and web links
- Christof Ziegert: Lehmwellerbau. Construction, damage and renovation . Fraunhofer IRB Verlag, Stuttgart 2003, ISBN 3-8167-6314-6 , ( reports from structural engineering 37), (also: Berlin, Technische Univ., Diss., 2002).
- Christof Ziegert: Article Lehmwellerbauten in Germany on the page Moderner-Lehmbau.de , accessed in February 2016
- Information on the Swiss IG-Lehm website , accessed in February 2016