Rethink Heritage

Clay is a natural material. It can be used as a solid building material or in bricks. The first system is dried in air, bricks can be either dried in air or fired. Adobe, as air dried bricks, is brittle material, fired bricks are much more durable (Vegas Mileto 2007). 

Daub, which is a mixture of clay, aggregate and water, hardens in the air, although it is still brittle. Cut straw fibres are mainly used for reinforcing clay, sometimes stone, for instance in France (Juvanec 2010). 

There are two systems of using raw clay: 'handwork' as kneaded daub and 'footwork' or rammed clay. Such constructions can use any dimensions, without traditional rules, the dimensions follow use: for both humans and animals. Adobe means the use of dried bricks, made by hand and dried in air.

Fired bricks are the same, but the dried bricks have to be fired at high temperature and need fire, energy.

Cob walling means construction in kneaded clay. The first technology is handwork. The most primitive method of working by hand is kneading, without the help of shaping work. This work has a particular problem: since the whole wall cannot be kneaded in one, it has to be divided into working stages (Juvanec 2010). This means the composition of a structure in sequences.

Cob structures have to be reinforced. Coniferous branches were used, juniper in Slovenia, also straw.

Cob constructions become harder and harder over the years. Cob cottages can be found in Slovenia some hundred years old in perfect condition.

Rammed technology consists of beating down selected earth (daub, clay) contained between a frame (two parallel boards) with a heavy implement. Compressing the material is important here, in order to squeeze out all the air, which would reduce the bearing capacity of the construction (Juvanec 2010).

A clay wall is not particularly hard and does not have an eternal lifespan. Both problems are solved by regular maintenance. Small cracks can be coated with a mixture of clay and water. 

Essential clay, aggregate and water needs to be mixed into a usable mixture by hand or more commonly by feet. The wooden mould is filled with this matter and squeezed with feet or a mallet. Construction belts, made in one day, are up to 50 cm high. After drying the wall, the mould is moved upwards for the next belt. The belts can still be seen on the finished wall.

The putlog holes that remain after the horizontal laths are removed become holes for ventilation in stables, in dwellings they are filled with the same material.

Rammed earth may be reinforced: in France stones are used, in Pannonia straw. The straw blades are cut into around seven-centimetre lengths – longer blades would reduce their strength because of moisture in the clay mixture. This would tear the blades and the mixture would become uncompacted. One hundred percent compaction is of great importance for a rammed construction. 

While construction is man's work, maintenance is the concern of the housewife, woman's work at least once a year. This is connected to the religious festivals: the house has to be freshly painted every Easter, the festival of spring. The walls have to be maintained before painting with lime plaster, which shuts all the possible cracks. 

Houses or towers in Yemen are built as many as eleven storeys high with this system (Oliver 2003, Vellinga 2007). They have a sort of self-maintenance system, whereby the sloping wall is drenched with run-off water (collected on the top from rainwater) and possible cracks concurrently coated (Juvanec 2010). Painting by hand is more or less only visual help.

Adobe is a clay brick dried in the sun or in the air, when the clay mixture of mud, aggregate, water and reinforcing material (straw) is pressed into a wooden frame, which shapes it.

The name 'adobe' is a corruption of the word 'dobie' (Spears 1986).

In a construction with smaller elements, a new problem occurs, since regular size requires an understanding of the system of ratios of dimensions. This must enable the horizontal composition in ground plan and in cross section, changing the rhythm of the composition and the constant ratio of length to width, since the length of the brick provides the thickness of the wall (Juvanec 2010).

The mould for adobe consists of boards, a composed cross construction of rectangles. The spaces of the grid are filled with clay, mixed with aggregate and water and reinforced – like in rammed technology – with straw. This mixture is filled into the frames, squeezed and levelled by hand or with wooden boards. After some days, the mould is withdrawn, and some days later the adobe bricks are turned and later dried in the sun in their side position. 

A wall with adobe is composed by overlapping the corners with the principle of alternation in all directions, including in height. 

The adobe system came to Europe from North Africa and is spread throughout all Mediterranean countries with a hot climate. 

Wattle is a construction principle of interlaced, wickerwork whole branches or split branches. Wickerwork shuts out all side views, not those from an inclination and is open to the wind, chill and heat. This system is suitable for drying devices and for storage goods, objects for living in wattle are extremely rare.

Wattle and daub is an unusual construction system: this is a combination of a wicker base and clay on both surfaces. Here is some uncertainty: is wattle and daub a construction system in wood, covered by clay or is it clay construction, reinforced with wattle.

Wattle and daub needs a frame, the system can be understood as filling panels in timber framing, especially in the upper parts of the gable. On the Pannonian Plain the walls of stables are made in this technique.

The proportion system is important in compositions with smaller elements, because the length of a log depends on the tree and a log house is adapted to the properties of the wood. The same is with boards, which define lengths in ramming – rammed walls can be constructed of different dimensions.

Bricks only are elements, which build and connect the wall composition. Bricks define the grid and practical dimensions of a wall, and the proportion between width, height and length is of extreme importance. The proportion theory has to be introduced as theory, but in practice the first requirement is overlapping.

Modular dimensions are needed for both adobe and fired bricks - as a result of the proportion theory.
The most compatible modular coordination uses an equation with duplicating numbers: 1, 2, 4 as height, width and length. Module 4 is defined as twice the value of 2 and 1 is half of 2. The modular grid for the elements composing a wall starts with and is multiplied by 'one'. This allows the walls a width of 2 or 4, composed in longitudinal or cross directions. 

The proportion theory is used regardless of dimensions. The wall can be composed in practice in the width of two or four modules: as a bearing wall in four and as a dividing wall as 2 modules. Outer walls have to be broad also because of better temperature isolation.