Sdružení hliněného stavitelství

The traditional technology

The regions of the half-timbered, the curb and the Danube houses meet in our country. The boundary area forms southern and partially northern Moravia. The traditional technology went through a long-run process which can be seen in well-preserved old buildings with a variety of types and forms. The massive structures of unburnt mud were mostly used, while some technologies weren’t preserved in our county. The main ways of applying mud in traditional engineering, that can vary a little in realization from district to district, especially in the term, can be divided into several basic categories:

  • an unburnt piece building – an adobe, hand shaped adobe
  • a pressed-down mud in the formwork
  • a layered mud, a pisé
  • dugout constructions
  • straw-clay constructions with wood
  • daubed
  • cobs
  • mortars and plasters

A mud that was accessible in given region was used for a production. Straw, husks, pig bristles, grit, gravels and granules, were added into mud in accordance with needs and a local tradition (they were found in the brick with sizes up to 40mm).

The mud was extracted one or two years before use in a mud-place at the border of village and it was left in a free heap under the influence of climatic changes, which caused homogenization and improved quality. However in some technologies it was extracted just before use (e.g. balls of earth).

Unburnt brick

(Another terms – adobe, cob brick)

A prepared mud was punned into a wooden forms, the bottom of the form was sometimes substituted by a pad. Brick size differs in its thickness (approximately 70 – 100 mm), length and width are usually about 150/300 mm.

The form is removed after pressing down and the brick is left to stay on the pad to exsiccation. The brick is moved to a place of natural drying after two days, is put on a side with spaces around 30 mm and is turned over regularly, protected against rain and sun. We can use the brick for construction after 3 – 4 weeks of natural drying.

The unburnt bricks were used for construction of vertical constructions like walls, sometimes also for wall footing. They were used for both external and the interior walls, bearing and non bearing walls included solid partitions. It is now find out by demolition or reconstruction of mud walls, that if the brick doesn’t disintegrate during pulling out of masonry due a previous overload, then it has usually strength 3 – 5 MPa.

The masonry of unburnt bricks forms the majority of old mud buildings at this time.


Fig. 1: The barn made of adobe

The balls of earth

The balls of earth – hand-made molded cylinders of straw and mud – are another variant of piece mud building material. The unburnt balls of earth weren’t allowed to dry out properly unlike unburnt brick and it was sufficient to prepare them just before construction. The mud was extracted only several days prior use. The balls of earth were again dipped before their stowing into the wall, in order to adhere better with each another, because the clay mortar weren’t used by this old technology, suitable for fast construction. The balls of earth were laid to wall aslope, in a characteristic ear bond that is known from antique as “opus spicatum”. The walled roll masonry that was left without a typical clay mortar in the case of barns or the boundary walls is very interesting by this structure. There is also a constructional variant, when a formwork was used.

Well preserved buildings of roll remained only sporadically, in Haná and in Znojmo.


Fig. 2: The barn made with the balls of earth

The pressed-down mud in the formwork

The light damp mud blend was pressed down in a moving wooden formwork. The pressing was made by a hand rammer, with special care for surface walls, in order to increase resistance to climatic impacts. This technology is less expanded in our environment, the walls were usually pargetted.


Fig. 3: The object with pressed-down mud

The dugout construction

The excavate spaces in mud in natural position. Mainly the wine cellars on southern Moravia were built this way.

Earth and straw structures combining wood

Earth blended with straw in accordance with the purpose, for which the blend will be used. Loam slurry was blended with 15 to 40 cm-long straw, reed or grass stalks. Then, this blend was twisted around wooden sticks. Made this way, the billets or rollers were then put into ceilings of outbuildings (cowsheds, stables); another possibility of using this building material was to deposit it in walls as a filling with half-timbered buildings.

Cobs and puddles

They were used for wooden and earth buildings.

Daubing the wattle of the wooden frame of a house with earth and straw slurry was one of the methods. Another frequently used method was daubing kerb structures with a thick layer of earth and straw slurry (about 150 mm) to protect the building against fire. For better adhesion, wooden pins were put in the kerb wall (the so called „hedgehogging“).


Fig.4 Kerb wall after uncovering the cob.
  
Fig. 5 Wooden walls cobs

Cobs

Cobs were widely used, not only for earth houses, but, later on, also for burnt-brick-built houses. They were even contained in the Czech Standard 1168-1939 (Bohemian and Moravian Standardization Society) entitled Carrying out bricklayer’s and associated works. Here is the quotation:

"Cob.

235. The cob is prepared from clean brick clay, evenly moulded with bond stuffs (chaff, awn, chopped straw etc.) while being sprinkled moderately. The ration between the bond stuffs and clay volumes is 1 : 1. The cob is applied in about 60cm-thick layers and rammed until the rammed layer lowers by about 1/3. The top layer is rammed particularly carefully several times until no cracks form.

236. There are the following types of cobs:

  1. standard loft cob (under the roof), which is applied in one layer, and after being rammed (after becoming compact) it is dusted with fine sand; usually, the ready cob is 8 cm thick;
  2. loft cob with insulation spacer; it is made as the cob described under a), however, a layer of impregnated felt is put on the frame construction before application (K 200/D in accordance with ČSN 1172);
  3. thrashing floor cob, which is applied in several layers and whose top layer is poured by beef blood or ammoniac water and sprinkled with ashes before ramming; the total thickness of ready cob is usually about 30 cm."

Puddles and mud plasters

Puddles used to be used for cob brick and stone structures, later on also for burnt-brick structures. The Czech Standard 1168-1939 (Bohemian and Moravian Standardization Society) entitled Carrying out bricklayer’s and associated works says:

"Puddle.

25. The puddle is prepared from earth and water. The earth must not contain humus elements and must be sufficiently binding (rich). The puddle must not crack after drying up; if it does not meet this requirement, sand or suitable earth must be added. Adding other fillings and binding elements (hairs, straw, blood etc.) must be prescribed."

Puddles used to be widely used, therefore one may have trouble establishing what technology was used to erect the particular structure. Barns and other outbuildings were left unplastered. The lower plaster layer was usually made from clay with chaff added to it while lime was added to the upper layer; the plaster was then completed by lime paint.


Fig. 6 The upper lime layer is on top of the chaff mud plaster.
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