The soil is one of the oldest building material used by man. Many buildings that were constructed with soil more than 3000 years are still in existence. The use of earth for building construction was learned and mastered by doing, and knowledge has passed down to generations. Even though many buildings constructed of natural materials, particularly earth, have stood the test of time, the construction of buildings out of these materials almost completely disappeared during the 20th Century.
The work on building Technologies at ASTRA (Application of Science and Technology in Rural Areas) began with the premise that one should emphasize the use of local materials, especially in rural construction. ASTRA did several experiments in mud construction which are summarized below for a better understanding of the general masses.
It was perhaps inevitable that mud became the first choice as a material for wall construction. Cob, Adobe, Rammed earth, bamboo reinforcement mud, and mud concrete are some of the conventional technologies in use. While these technologies are excellent for economic and ecological soundness, their performance depends on maintenance input. Very often a heavy and instance rainfall can lead to the collapse of old and poorly maintained mud walls.
Some experiments were carried out at ASTRA to generate better alternative in mud wall construction.
- Unstabilized mat block
- The part-stabilized mud block
- Stabilized mud block
- Waterproof coatings and plaster for un-stabilized mud walls
- Waterproof coatings for stabilized blocks
- Rammed Earth for walls
- Stabilized Adobe
- Stabilized mud concrete
Unstabilized Mud Block :
The term and stabilized mud blocks refer to a building block made by pressing the local soil in a manually operated press at near optimum moisture content. The blocks initially were used in few construction projects but the result was not satisfactory.
Subsequently, it was felt that pressing plain mud in a machine is not very superior to making an Adobe block. The sun-dried Adobe develops a good density due to all around shrinkage does obviate the need to densify using manual energy. It is hence evident that whenever using plain mud is a valuable option, it is enough to hand mold it in a simple shape rather than use a more expensive / labor intensive machine.
Part Stabilized Block :
Whenever a mud block is used in the wall construction, only one face of the block is exposed to Sun and rain. One way to reduce cost is to stabilize a thin layer of the block behind the exposed surface. The process can be done in a mud block press by using a separate plate to keep stabilized soil temporally apart from the plain soil. The two layers are then compacted after removing the separator plate.
Stabilized Mud Block :
One of the most satisfactory building blocks is made by stabilizing sandy soil using cement or cement and lime or lime alone and pressing it in a machine. Stabilized Earth Blocks require moist soil to squeeze under a high amount of pressure to form blocks. The main constituents are of the dry inorganic subsoil, non-expansive clay, aggregates and Portland cement. most of the times, they are stabilized with cement or lime. With cement stabilization, the blocks must cure for four weeks after manufacturing. After drying, they can use it with a soil cement stabilized mortar.
Read more about – Compressed Stabilised Earth Block (CSEB)
Waterproof Coating and Plaster :
The major problems with mud walls may be listed as under.
- erosion of wall surface due to rain impact
- loss of strength due to water leakage from the roof
- termite infestation
Waterproof Coatings :
Laboratory experiments were made with coatings like the whitewash, animal glue base paint. Use of the combination coating- 4 coats of whitewash followed by two coats of 15% animal glue solution was done. This example showed the usefulness of such simple coatings to prevent rain erosion. It is also to be understood that every coating like this may have to be repeated once in a few years for long-term durability.
Waterproof Plaster :
A plaster formula known as lime soil plaster was developed. This involved mixing involves mixing of lime- soil-sand approximately in the proportion of 1:2:5 add using this for plastering. This plaster has an excellent addition to a stabilized mud walls. Addition of some amount of cement will enhance the addition and strength of the motor. However, the plaster is quite weak in compression. Further another coat in the form of lime rendering has to be carried out make the plaster waterproof.
Waterproof Coating For Stabilized Blocks :
Protection to stabilize blocks from the effects of rain and sun is often desirable. Some options are available to facilitate this. Use of transparent silicone Paints is one option. It, however, needs to be repeated once in 5 years. Polyurethane-based varnish often used for wood has also been applied. Again, this also needs to be repeated once in 5 years. Three quotes of whitewash are also quite useful in reducing moisture absorption.
Rammed Earth :
Rammed earth is a mixture of soil, usually a sand/clay type of soil, with some binder, like Portland cement or asphalt cutback that is mixed together with about 10% by weight of water. Layers of soil are rammed into a high-density wall unit using a simple formwork consisting of two parallel boards held in place. This is an in-situ construction technique which avoids masonry bonding.
Stabilized Adobe :
Production of Adobe is one of the most straightforward processes for making building blocks. If soil can be stabilized while making Adobe, it can indeed be a direct and cost-effective method. Some attempts were made by using cement, cement, and lime with soil to make so-called stabilized Adobe.
It is now clear that for stabilized Adobe, we need to use lime always, either alone or with cement and a high proportion of sand. Solar curing can increase strength with a negligible cost increase.
Stabilized Mud Concrete :
Cement stabilized soil can be mixed with coarse aggregate in the proportion of stabilized soil: aggregate of 1:1.5 to 2 by volume. The soil itself may be stabilized with 10% cement after ensuring adequate sand content. It may be noted that sufficient water may be used to meet workability requirements of the concrete.
The experiments carried out by ASTRA have conclusively shown the value of construction with stabilized, unstabilized and part stabilized mud. Each version can be appropriate in a specific contract depending on cost and performance expectations. Use of waterproof coating, lime, cement and soil based plasters can vastly enhance the performance of mud block walls.