• Steel rebar can be placed into the form and bound to the earth during the ramming process. This can occur at corners and over wall openings to provide stability and tensile strength.
• Instead of rebar, lintels of various materials or even arches can also be used over openings.
• The specific construction of rammed earth consists of “lifts” or layers of earth poured into formwork at a depth of eight inches and then compacted to five inches. This creates a striated earthen wall.
• Similar to concrete, it is stronger than other forms of earth construction because it is compacted in place and contains no mortar joints.
• Generally more compaction will give higher strengths and smoother finishes but too much compaction can lead to fracturing and less strength.
• Care is taken so that larger stones are moved away from the form. The edges are rammed first, and then the center until no further impressions result from blows from the tamper.
• There are machines developed for ramming the walls.
• Refined formwork systems and electrical or pneumatic ramming reduces labour input significantly and makes rammed earth techniques relevant in some industrialised countries as well.
BUILDING PROCESS – Construction(rammed earth)
Problem Solution
53
61. Pneumatic rammers
60. Hand rammers
BUILDING PROCESS – Construction(rammed earth)
Problem Solution
Some claim that it is possible to achieve with unskilled labour.
A contractor skilled in rammed earth would have to be available for acquisition of materials, testing, and designing formwork. However, after that, the process of mixing, hydrating, lifting, and tamping is possible by unskilled labour.
Much of the general concern
• Common design techniques, such as deep over hangs (usually one-third the height of the wall), can begin to protect the wall.
• The addition of a stabilizer will help with the water absorption. But as far as water damage goes, surface treatment can provide the best protection for a rammed earth wall. Breathable finishes should be used to allow for water evaporation. DPC should be added always to solve water problems.
• Traditionally, stucco or plaster has been used and then painted over the rammed earth walls. Also, a lime wash (whitewash), bitumen emulsion with paint, emulsion paint, or oil-based paint can protect the surface. Still, with the desire to express the earthen quality of rammed earth, polymer emulsion (PVA) has more recently been used to seal the wall and protect it from wind and rain, left transparent for aesthetics
Needs manual labour for adjusting, erecting and dismantling the formwork.
• The labour input in traditional rammed earth walls constructed manually, including preparation, transportation and construction, is from 20 to 30 h/m3. By refining the formwork system and using the electrical vibrator.
• Transportation and filling is done by a dumper and compacted by heavy pneumatic rams, labour input can be reduced to as little as 2 h/m3, which is only 10% of the labour used with traditional techniques, and significantly less than that needed for masonry work.Proper designing and choosing of formwork can lead to decrease in manual labour almost by 60%.
• Boards must be stiff so that they do not bend outwards while ramming is underway.
• All parts must be light enough to be carried by two workers.
• The formwork should be easy to adjust in both vertical and horizontal directions.
• Variations in the thickness of the wall must be controllable within a specified tolerance.
• It is preferable that the edges require no special formwork. Therefore, the formwork should allow varying lengths of wall to be cast.
“During the late 1700s, a French builder named Francois Cointeraux founded a school in Paris to study and publicize rammed earth construction, which he called pisé' de Terre (puddle clay of earth). Today, David Easton has developed a new version of rammed earth construction he calls PISE (Pneumatically Impacted Stabilized Earth). It involves spraying the prepared soil under high pressure against a one-sided form. This technique can produce 1,200 sq ft (365.76 sq m) of 18 inch (45.72 cm) thick wall per day, which is four times faster than a typical, four-person crew can fill box-like forms and compact earth with power tampers.”
BUILDING PROCESS – Construction(rammed earth)
54
62. Earth projected on one side wooden planks to create a wall
BUILDING PROCESS – Construction(rammed earth)
Problem Solution
• In nearly all traditional rammed earth techniques, the formwork is removed and re-erected horizontally step by step.
• This means that earth is rammed in layers from 50 to 80 cm high, forming courses of that height before the formwork is moved.
• When one course is complete, the next course that is rammed is moister than the one already in place, which is partially dried out.
• Therefore, there is a higher shrinkage in the upper course than in the lower, leading to horizontal shrinkage cracks at the joint.
• This can be dangerous, since water can enter this joint and remain, causing swelling and disintegration. Vertical cracks can also occur in such walls.
• This problem was solved by using a layer of lime mortar above each course before laying a new one.
• A lime mortar cures over several weeks and remains plastic until the loam has stopped shrinking; sometimes even the side joint between sections of the course is made with mortar at an incline.
Related drawings
55
BUILDING PROCESS – Construction(rammed earth)
Problem Solution
As with rammed earth techniques, the cost of the formwork is quite high.
• In some cases, it is preferable to use a thin masonry wall or stiff thermal insulation elements made of wooden materials as lost formwork, so that either no formwork or only one-sided formwork is required.
• It is also advantageous if this formwork can contribute to a substantial increase in thermal insulation. The stiffness of this lost formwork has to be sufficient to take care of the lateral impacts created by ramming.
• The inner leaf can be made from adobes or soil blocks, larger pre-fabricated loam elements, or stiff plywood boards, fibre-reinforced gypsum boards, or wood particleboard. Protection of the wall surface against the elements can be achieved by plaster, masonry or timber panelling with air cavity.
• The first two cases show an inner leaf built of adobes or soil blocks and an outer rammed earth layer made with lightweight mineral loam which is directly plastered. In this case the formwork is only required for the outer face.
• In the second case, a somewhat better stiffness of the inner adobe or soil block leaf is attained due to the bonding pattern in the components.
• In the section shown on the right, the lost formwork is on the outside and is made from stabilised lightweight soil blocks.
Related drawings
56
BUILDING PROCESS – Construction(rammed earth)
Problem Solution
With traditional formworks, the boards on both sides are held apart and kept together by spacers. These spacers pierce the wall, causing openings that must be filled in after removal of formwork.
Formworks without
intermediary spacers which are braced on both sides require a lot of space and hinder site movement.
• A system with very thin tensile spacers (4 x 6 mm) penetrating the wall has been developed.
• Formwork for curved walls is also possible .
• With a special formwork, rounded corners and curved walls can also be formed.
• In order to completely eliminate this disadvantage, spacer-free systems have been developed.
• one-storey-height panels, with widths of up to 2.4 m, in a continuous ramming process. This technique avoids horizontal joints, and the vertical joints that occur are closed only after the shrinkage is complete.
• For lateral stability, the vertical joints are made in a tongue-in-groove pattern.
Related drawings
57
63. 64. 65.
63. Unit created by vertical formwork
64-65. Process showing vertical formwork for rammed earth
BUILDING PROCESS – Construction(rammed earth)
Some potential methods for making loam walls with improved thermal insulations are being developed.
with a stabilizer, the process is a bit more complicated and expensive
• Reasons for adding a stabilizer far outweigh not, as it speeds the construction process, improves durability, allows thinner walls, and requires less of a surface treatment.
• If a stabilizer has been added (especially cement), lifting the wall must begin immediately thereafter.
Plastering a rammed earth
wall • A rammed earth wall requires less labour and material inputs for surface treatment compared to walls made using other earth construction techniques.
• As a rule, it is neither necessary nor advisable to plaster a rammed earth wall. If the surface is sponged with a moist felt trowel immediately after dismantling the formwork, then a smooth surface is easily produced, one that may be painted or wallpapered (in cases involving interior wall surfaces).
• If exterior surfaces thus treated are sheltered from rain by roof overhangs and against splashing by a plinth, a coating of paint is sufficient to protect them against the elements. Care should be taken that coatings neither peel nor crack.
Related drawings
58
66.
67.
71.
70.
69.
68.
66. insulated rammed earth wall section and view 67. Imprints on rammed earth wall made while
creating formwork 68. Formwork for curved walls 69. Formwork for circular unit 70. Insulated rammed earth wall detail
71. Corner junctions and columns of rammed earth