Making Of A Shuttering

Figure 13.19 shows a Swedish model that is easily self-built. It consists of two vertical panels fixed together by long bolts and wooden rods.The panels are made of 30 mm thick planks of spruce or pine.The length of the shuttering should be between 2 and 4 m depending upon the dimensions and form of the building. The panels are 80 cm high and braced by 7 x 12 cm posts screwed to the boarding.The screws are 64 cm apart.

The spacing of the posts depends upon the thickness of the wall, usually 40 cm. On the bottom they are held together by timber rods, whilst the upper parts are held together by steel bolts 18 mm in diameter. The rods are made of hardwood such as beech, ash or maple and are conical. The dimensions at the top of the rod are 6 x 6 cm and at the bottom 4.5 x 4.5 cm. The holes in the posts should be slightly larger so that the rods are loose. The gable ends of the shuttering have a conical post fixed with nails. To prevent the shuttering falling inwards, a couple of separating boards are needed inside the shuttering.

In order to form openingsfordoors and windows, loose vertical shuttering is placed inside and nailed through the shuttering panels.These can then be easily removed. It is quite possible to mount shuttering after each other as long as they are well fixed.

The ramming can be done either manually or by machine. When ramming by hand, ideally three rammers with different forms are needed (see Figure 13.21). The handle is heavy hardwood and the rammer is made of iron. The weight of a rammer should be around 6-7 kg.

Ramming by machine is much more effective. This can be done using an electric or pneumatic ram with a square head of 12 x 12 cm. A

13.20

Ramming earth with pneumatic equipment. Source: Claytec.

13.21

Manual rammers.

13.21

Manual rammers.

robotic rammer which can follow the line of the shuttering is being developed in Germany.

Ramming is best carried out by a working team of two or three people. The wall shuttering is mounted on the foundation walls as in Figure 13.22 with gable ends and separating boards.

When ramming by machine, layers of 13 to 14 cm can be made. This is approximately two-thirds of the volume of the original loose earth. When ramming by hand a layer thickness of not more than 8 cm is advisable. It is important to ram at the edge of the shuttering when machine ramming; starting in the middle may cause stones and lumps to be pushed out to the edge and loosened. The ramming should make the earth as hard as rock - it should 'sing out' - and a pick should not make marks when the surface is hit.

13.22

Putting up shuttering.

13.22

Putting up shuttering.

13.23

Ramming in the wall plates to carry structures in roof and floors.

13.23

Ramming in the wall plates to carry structures in roof and floors.

When the first layer is ready, the next layer is begun, and so on until the shuttering is full. The rods are then pulled out and the shuttering moved. With each move it is necessary to check that the shuttering is exactly vertical. The conical post on the gable end of the shuttering forms a 'locking key' which is used to increase the stability of the wall.

In the corners, traditionally reinforcement of twigs or barbed wire is used, and after the first layer, holes are cut for the floor beams, which can be placed directly over the damp-proof course on the foundation. As the ramming progresses openings for windows and doors are added, with timber or reinforced concrete beams rammed in over them. Timber does not rot in normal dried earth walls. All timber that is rammed into the walls has to be dipped in water first, and trunks that are rammed into the wall for fixings should be conical, with the thickest end inside the wall, so that it will not loosen. To support the floor joists further up the wall, a timber plate must be rammed in (see Figure 13.23).

When ramming is finished, the holes made by the rods are filled with crushed brick or expanded clay aggregate mixed with a mortar based on lime or loam. After that the roof is put on. A large overhang will protect the wall from rain.

Adobe (earth blocks)

The advantage of building with blocks rather than pisé is that the building period can be shortened. The blocks can be made at any time, providing there is no frost, and can be stored until needed for building. The construction work should be carried out during spring or early summer so that joints can dry out before applying a surface rendering. As already mentioned, there must be a higher percentage of clay in earth for blocks. There should be no particles larger than 15 mm in the mix. Hard lumps of clay can be crushed in special crushers (see Figure 13.24).

A certain amount of coarse plant fibres, such as chopped straw, is usually added to stop cracking due to shrinkage, and just enough water to make the earth more pliable before use.

13.24

Manual clay crusher.

13.24

Manual clay crusher.

Moulds. Loose moulds of wood or metal, and even mechanical block moulds, are available. The size of moulds can vary, but 'monolithic' blocks are usually 75 x 320 x 50 cm and mini-blocks are the same size as bricks. Larger blocks for use in partition walls are made in dimensions up to 520 x 250 x 100 cm; these are commercially available in large parts of Europe. Such blocks are often made with significant amounts of wood shavings added, and may be perforated to reduce weight and facilitate drying during production.

Simple wooden moulds can be nailed together quite easily. Mechanical block moulds have capacities that vary from 300 to 3000 blocks per day. These are easy to transport and are used manually or driven by a motor.

Pressing the blocks. The earth mix is rammed into the mould, ensuring that the corners are well filled, and excess earth is then scraped off with a board. After a few hours the blocks are ready to be removed from the mould, and after that be stacked so that air can circulate around them. This should take place in the shade and

13.25

Adobe. Gaia Lista, 1991.

well protected from rain. After two weeks the blocks are dried well enough for building.

Laying earth blocks. The mortar used is usually the same earth that the blocks are made of, mixed with water and even some lime. Mortars based on Portland cement should not be used as they are less elastic and can split the earth during shrinkage. Blocks are laid in normal coursing, often after being dipped in a waterglass solution to saturate them. Barbed wire, chicken wire or plant fibres are recommended in every third course as reinforcement. It is also possible to construct ceiling vaults from earth blocks.

Good protection against moisture and rising damp are critical. In rough climates a good rendering or other cladding is advisable in any case, see page 216.

Other earth-building techniques

Adobe and pisé are the most widespread of earth-building techniques, but other techniques also have interesting aspects. The most important alternative techniques are cob, earth loaves, earth strand technique and earth filled hoses.

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