Consistency

Silt and silt bound building materials are soluble in water, in principle. If the hardened earth is worked on with enough water, the consistency reached through drying is reversed. The material becomes ductile and moldable. In this sense silt earth is the only building material that can be reused unrestrained and without quality loss. The water solubility is of course a problem for the weather and erosion proofing of earthen buildings. A lot of experiments and developments go into the direction of annihilating this quality from the silt and making it more durable for wetness. With supplementing cement this can be reached to a certain extent, however other very positive characteristics of the silt earth will be impaired.

There are certainly many design options to avoid the use of cement. These constructive design measures are integrated in the wall structure and will reduce the abrasion intensity. This form of abrasion occurs whenever water flows down the wall. If water on the façade runs off too quickly, it will sweep away particles of the material; if it runs off more slowly, then that much more loam will remain. Rammed earth walls should thus include erosion checks in order to slow the velocity of water flow along their surfaces. These horizontal layers can consist of stones and fired clay elements that protrude from the façade, or else of trass-lime mortar courses that run flush with the wall plane. They have the same effect in any form of construction: the water flow decelerates, and with it erosion. The material itself naturally inhibits erosion: after the first few years, the outermost loam layer will have been washed away and more stone will be exposed, making the wall surface rougher. As such, it contains its own mechanism protecting it from erosion, since the uncovered gravel stabilizes the wall. The earthen seams in between the stones are now recessed deeper into the façade and expand when exposed to rain. This swelling process ensures that water does not penetrate further into the wall, the cumulative effect of which is to halt erosion. Since it can be predicted and controlled by checks, this process is referred to as calculated erosion. It must be integrated into the design and technical planning. This also means that a rammed earth wall requires several years before it reveals its finished surface

Silt earth shows a equilibrium moisture content of about 6 to 7 %, which means it is dryer than wood, but has the ability to absorb dampness out of the air very fast and releasing it at the same speed. Although this fast drying quality the rammed earth constructions need to be shielded well against moisture penetration, especially from above through constructive measures.

In order to avoid ascending moisture the walls are placed on a concrete plinths which rise 35cm out of the fastened or unfastened soil. As a horizontal isolation between the concrete and the rammed earth bitumen sheeting is spread out. For the coping of the wall crest and the outside of Parpetten, metal sheets or ceramic tiles can be used with projections of 5 to 15 cm according to the wall height. The lintels of windows and door openings will be built in during the compression of the mixture into the mould, with the load being transferred off to the side. The undersides of lintels are constructed in concrete (pre-fabricated) or done in steel. In the case of larger door openings or window series, reinforced concrete bands made of site-mixed concrete are integrated into the earthen walls.

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