21a – More about adobe and rammed earth

Rammed earth is one construction technique that is experiencing a healthy rebirth all over the world.

  

  

Another well known construction technique, wattle and daub, has been used in the construction of low cost dwellings as well as not so low-cost buildings in many parts of the world. 

  

 

In an article I published in my mestiçagens blog about a year ago I mention a couple of Internet sites that, even though written in Portuguese, describe very clearly this technique.

 

One of these sites, Chácara da Boa Vista, describes the manufacture of adobe bricks. In the other site, howstuffworks, Fernando Bussoloti describes the rammed earth technique as well as other nature friendly construction methods and techniques.

21 - Mixing soil for compacted earth blocks (CEB)

Compacted Earth Blocks (CEB) are some of the best construction materials we can find. They are and have been used in many parts of the world for many centuries and have proved to be worth a lot more consideration than we sometimes give them.

As the name indicates they are made out of soil that is compacted in a simple press and cured in the sun. They are not fired and are more resilient than adobe blocks. It is much easier to build with CEBs than to build with rammed earth.  

They are often manufactured in the location where the dwelling will be built. CEBs can be made with soil components only. But they can be stabilized with lime or cement to be more durable.

 

Since they do not consume fuel for the firing process CEBs do not contribute to climate change and deforestation. The manufacturing process uses 5 to 15 times less energy and is about 8 times less polluting than other types of blocks and bricks.

All these factors contribute to a lower production cost when compared to the available alternatives.

The CEB manufacturing process and the many construction methods using CEBs are well documented in many languages. For that reason we will only cover here some basic points on how to get the right soil mixture.

 

Raw materials

  

The basic raw material is soil with a good mix of gravel, sand, silt and clay. This type of soil can be found in many locations around us. These locations are well known in all communities and there is always someone who knows where they are.
 

This good soil is found under the ground layer of topsoil. Topsoil is where plants grow and will always contain a large amount of plant and animal matter. The soil in topsoil is not good for what we need. We need the more reddish soil as shown in the picture above.

Soil identification
 

To identify the type of soil we have we use the same identification method we used to make adobe blocks.

  
The above picture shows some examples of the type of results we may get. The percentages always refer to the total amount of soil in the sample. The water used and left after the test has no impact on the results.

The right soil mixture

A good soil mix for CEBs has the composition shown in the picture below. If the soil collected from the local source does no have this mix we need to add more of one of the other component until we do. It is important that our soil sample does not contain rocks or organic material such as found in the topsoil.
 

 
First we need to make sure that our soil is well ground up and has no lumps. Then we mix all the components well without water. Only then do we mix water until we get a humidity level that will allow us to make a ball in our hands. But our hands should not be wet after making the ball.
 

 

When we drop the ball from waist height the ball should break in pieces like the example in the middle of the picture above. At that point we have a good mix to make our CEBs in the press.

We may add about 5% of lime or cement to obtain a good stabilization. This makes our CEBs more resistant to breakage and more durable. Stabilized CEBs need to cure in air for about four weeks.

 

04a - A dwelling with good ventilation

To have good ventilation in a dwelling without fans and air conditioning units we have to create what is called the stack effect or the chimney effect.
   

 

The stack effect takes place when cooler air coming from the outside flows into a building, preferably at floor level, and warmer air, humid air, smoky air loaded with unwanted smells, leaves the building through an opening close to the ceiling.

This stack effect can be very efficient if the dwelling is built in such a way as to benefit from the wind that regularly blows in the area as represented in the picture above.
  

Let us examine some practical details of a well ventilated and insulated dwelling built to minimize the accumulation of humidity.
  
We will start with the foundations.
 

  
The foundations should be built with stone and cement or concrete blocks. These materials make them more resistant to the humidity in the ground. The foundations must be built so that the base of the walls and the floor of the dwelling are kept about 10cm to 15cm (4in to 6in) above the level of the surrounding terrain. The soil under the foundations should be well compacted and firm.
    

 

 
Fill the space inside the foundation walls with rubble, soil or a mix of soil, gravel, sand and stone and compact very well all this filling material. Do not leave in topsoil that contains organic material.
  

In this example we are building the walls with brick, adobe, mud, rammed earth or compacted earth blocks (CEB). All earth/mud based construction materials are much better insulators of heat and cold than concrete based materials. These materials need some regular maintenance and the roof overhangs need to be wide enough (40cm to 50cm or more) to protect the walls from the falling rain but it will be worth it.
  

  

 
Now that the walls have been built we can build the roof.This will be built in the habitual way. With wooden beams, joists and sticks to form a grid, the structure over which we will apply the metal sheets that will make up the roof itself. To protect the walls from the falling rain the overhangs should be 40cm to 50cm wide or more depending on local weather conditions and practices.
  

  
We could install the insulation before installing the roofing metal sheets. The insulation will go well between the roof beams. In this case we can use some matting to cover the underside of the insulation to make it visually more appealing. This insulation will protect the interior from the heat of the sun and from the cold outside.

 
After we install the roofing metal sheets (cement fiber or plastic sheets), still a good protection against the rain, our dwelling will be ready to be occupied.
   
There are some important details worth highlighting to be included while the walls are being built.

Windows and air vents
  
A good solution for the windows is to install top hinged shutters as shown in the picture. This configuration makes good protection against the sun and the rain. With these we do not have to run to close the windows when it rains.
    

   
Air vents should be as close to floor level as possible. At ground level air is always cooler.
 

  
Intake air vents can be protected from the outside with bars or strong wire mesh, and from the inside with shutters as shown in the picture above. Always close to the ground and on the windy side of the building if at all possible. If there is a shady side of the building, it is worth placing the air vents on that side because the air will be cooler there.
 

  
Exhaust air vents should be built as close to the roof as possible. In this example these vents were placed between the roof beams and protected with strong wire mesh. On the inside we can also install shutters. Exhaust air vents should be on the side of the dwelling opposite to the wind.

 

 
In this example we can see a window protected with top hinged shutters, an air intake vent protected with wood slats for better air circulation and two exhaust vents between the roof beams protected by a wire mesh.
 
Notice how the exhaust air vents are close to the roof.

When we install the insulating material we need to keep it away from the vents to ensure good air circulation.

 

From the inside it is easy to see the space left around the exhaust air vent.

  
The insulation material, using natural or manufactured materials, can be attached to the roof beams with wires, wire mesh, string or other materials.

Important points
 

We chose a simple dwelling as our example. Each one of us can modify these ideas and use additional ones. The windows may have glass panes or not. There may be bars on the windows or not. It all depends on the situation. But it is important to leave the openings required for windows and air vents when the walls are being built.
 
What is really important is:

• Foundations that are above ground level
• Earth products (mud) for the walls
• Metal sheets (or plastic sheets) for the roof
• Insulation on the inside of the roof
• Intake air vents close to floor level
• Exhaust air vents close to the roof/ceiling
• the behavior of the dwelling occupants

And a bit of imagination and creativity. 
  
Our habits
 
The behavior and living habits of the occupants is also very important. For example, during the night the air outside is cooler and we should open the intake air vents to cool off the inside of the dwelling. During daytime, when it is hot outside, we should close the intake air vents to keep the inside cool.
  
During the cooler months it may be more comfortable if we open the air vents during the day to allow the warmer air in. This air will warm up the inside of the dwelling and help get rid of humidity. At night it may be better to close the intake air vents keeping in the warmth accumulated in the walls during the day.

A well insulated and ventilated dwelling responds well to our behaviors. We change clothes according to the weather. We should also make use of shutters, air vents and insulation to accommodate to weather changes.