Mud house design competition

Reinventing the African Mud Hut Together

Nka Foundation invites entries for Mud House Design 2014, an international architecture competition open to recent graduates and students of architecture, design and others from around the world who think earth architecture can be beautiful.

Registration and submission of entries run from March 15, 2014 until August 31, 2014.

The challenge is to design a single-family unit of about 30 x 40 feet on a plot of 60 x 60 feet to be built by maximum use of earth and local labor in the Ashanti Region of Ghana. The client of your design is the middle-income family in any township of your choice in the Ashanti Region. Total costs of constructing the design entry must not exceed $6,000; land value is excluded from this price point. The entry should serve as an example to the local people that mud architecture can be beautiful and durable.

What is the design problem? The cause is this: in Ghana, as in other countries in West Africa, stereotypes about buildings made of earth persist because of poor construction. Earth architecture is fast giving way to modern dwellings made of cement blocks and other modern materials that are not simply expensive but thermally and acoustically problematic. From the cities to the low-income villages, use of concrete – despite its dependence on imported resources – is considered indispensable for building. The rising cost of the modern building materials manufactured from imported resources makes it very difficult for low-income families to become homeowners. Yet an excellent, cheap and local alternative called laterite, red earth, is available everywhere in Ghana.

Contact: info@nkafoundation.org

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Reflections and observations on a recent visit to the former Transkei

I had the pleasure of recently visiting a really magical place, Mdumbi in the former Transkei. Mdumbi is about 30km north of Coffee Bay in the typical rolling green landscape. Travelling with fellow architects Carl Morkel and Wim Els at a slowish pace, either walking or watching from the car window, one is aware of a soft silence, endless, gentle rolling hills with the silhouette of small pastel huts and sometimes the ocean in the background. Grandmothers moving peacefully and slowly, a shout from one hillside to the next, fishermen just appearing as almost out of nowhere.

Figure 1: Typical Transkei landscape, round huts in pastel colours.

Figure 1: Typical Transkei landscape, round huts in pastel colours.

One would like to think of this place as the ultimate sustainable example of natural building. Huts have been made here forever with soil and clay, either with using the wattle and daub or with mud brick method. You could easily imagine that all buildings here are still made with the smallest possible footprint on the earth. There are tiny mud brick making “factories” all along the roadsides, with clay being excavated directly out of the hillside and the small holes being covered with grass growing over it fairly quickly. People are going about making the bricks, talking, mixing, moulding, laying the bricks out to dry.

Figure 2: Local mud brick factory with possibly best view in the world

Figure 2: Local mud brick factory with possibly best view in the world

Figure 3: Local mud brick factory with possibly best view in the world

Figure 3: Local mud brick factory with possibly best view in the world

 

Deep-rooted traditions, foreign to outside observers, is visible in the very nature of the buildings, with huts in ruins not because of a lack of maintenance but out of respect for the inhabitant that has passed to another life, with contemporary car tyres forming the crown of the round roof and sharp pieces of glass embedded in them, not for adornment or ornament, but to keep the evil owl away.

The “evil” that has crept into this landscape dispels the romantic idea that all here is inherently sustainable. The landscape is pock marked with entire hill sides being bull dozed to mine sand and left un-rehabilitated. Thermally poor performing materials with a high environmental cost, such as concrete block have become the status symbol for affluence. Understanding of all the reasons behind these changes, which are many, is the topic for another discussion, but the low maintenance of a concrete block building cannot be left out of the picture.

The “charm” of the degradable, organic buildings is thwarted by the very aspect that makes them charming. If just left, they can degrade. Easily. The national “eradicate mud schools” agenda is by now well known. It is a multibillion-rand programme. This year alone the delivery delays on this programme have apparently cost 7 billion rand. (Legal Resources Centre, 2014) The mud school has developed a very bad name. And it is only through involvement and education that this will change.

Figure 4: Wattle and daub degrading

Figure 4: Wattle and daub degrading

The reasons for the mud schools have a bad name is given one blogger as “having no toilets, having no electricity, having not water, coughing in a dusty classroom where the roof is caving in”…………..this from http://realisingrights.wordpress.com/2014/01/31/we-do-not-have-toilets/ Also read this http://mg.co.za/article/2013-03-08-00-forgotten-schools-of-the-eastern-cape-left-to-rot and this http://www.news24.com/SouthAfrica/Politics/Mud-schools-gone-by-2015-minister-20130226.

Why do these school buildings perform so badly? Traditional Transkei buildings require constant maintenance, since most of them lack the two really important protection criteria that natural buildings need to survive. A proper hat and boots. In trying to convince role players that it is not necessarily the “mud” that is the problem in these schools, Lesley Freedman and Andy Horn recently met and then sent a letter to Equal Education to introduce ideas around proper “mud” building standards that will not only improve the schools but also houses in the surrounding villages.

This brings me back to our reason for visiting the Transkei. We went there to take part in discussions regarding the development of a wonderful initiative, Mdumbi Green Destinations. This is a project envisioned by Mdumbi Backpackers in association with the Mankosi community. The Mankosi community will develop a community owned tourist facility where, amongst other sustainable aspects, the buildings will be made with natural, local materials. The local community will be integrated in the design, development and building process and will, apart from getting ownership and employment during and after the process, they will learn about using their local materials in an effective way that makes it last longer (and of course food production and other environmental sustainable things, but we are concentrating on this blog on natural building).

Spin offs of the initiative is that the Mdumbi Backpacker community has learned some valuable lessons and skills about natural building in the long process (read years) towards the project becoming a reality. And some of them learned these skills at Berg-en-Dal.

Through the Transcape “arm” of Mdumbi backpackers that focuses directly on assisting the community, an Eco Centre has been opened. Already here mud brick making, proper building methods (and food gardening) is taught to the local community. What is interesting that we observed when visiting the Eco Centre is that it was predominantly young men and women that took part in the mud brick making workshops, where at the “factories” next to the road it was mostly older women working.

Figure 5: Me at the Eco Centre mud brick training facility

Figure 5: Me at the Eco Centre mud brick training facility

Figure 6: One (wo)man mould_I like the size of this for when you work alone

Figure 6: One (wo)man mould_I like the size of this for when you work alone

Figure 7_Local stone_great to use for “boots” of the building

Figure 7_Local stone_great to use for “boots” of the building

 

Figure 8: Volunteers house at the Eco Centre – putting in proper floor

Figure 8: Volunteers house at the Eco Centre – putting in proper floor

So, I am really looking forward to being involved in this great project and will keep you updated……………..

 

Figure 9: Sunrise and fishermen at Mdumbi Point

Figure 9: Sunrise and fishermen at Mdumbi Point

 

Photo credits

Figure 1-8: Carl Morkel

Figure 9: Hermie Delport-Voulgarelis

Disclaimer

Understanding Earth II: Testing earth

By Peter McIntosh

(Please note that in order to understand what is written here you will need to have read my previous post on understanding earth)

 

Earth requires two properties to make it strong enough for building, compressive and tensile strength. In much the same way that steel works in concrete they can’t be looked at in isolation as they work together. For example, even though concrete when supported can take an enormous amount of pressure / compression without disintegrating, if you were to cast a concrete lintel without steel and suspend it between two points and apply pressure / tension, it would snap. Steel has enormous strength in tension while concrete has enormous strength in compression.

Compressive strength is measured in Megapascal (MPa). One atmospheric pressure is 101 325 Pascal; a Megapascal is more-or-less one million Pascal, or 10 times atmospheric pressure. In other words, one MPa is 10 times stronger than it needs to be to resist the force of gravity on earth, stand on its own and not be crushed.

A good mud-brick has a MPa strength of around 1.6 to 1.9 MPa, while a clay-fired brick has an MPa strength of around 14. Concrete ranges between 15 and 25 MPa. Obviously these figures vary widely, but these are good averages. A mud-brick at 1.4 MPa is 14 times stronger than gravity, a clay-fired brick at 14 MPa is 140 times stronger than gravity or 140 atmospheric pressures.

Tensile strength is found in all material, just in varying degrees. Concrete as we have seen has high compressive strength but relatively low tensile strength. The addition of steel (reinforced concrete) increases its tensile strength. Mud bricks can handle 14 atmospheres, but like concrete they have poor tensile strength. However, as clay is somewhat plastic in its behaviour it’s not as poor as one may think. This is why the addition of straw to a mud brick is essential as it not only increases the insulation value of the mud brick but also acts like steel in concrete. (I am told that weight-for-weight straw is stronger than steel or at least in the same realm.)

In short, the tensile strength of a material is its ability to resist snapping and cracking. Increasing the hardness of an earthen material, for example by adding lime, may not increase its tensile strength or resistance to cracking, as it may end up becoming less plastic and more brittle. Thus, clay buildings are often more resistant to cracking because they can absorb the movement that harder more brittle materials may not.

When building with earth, strong enough is what you are aiming for. At 1.3 MPa, a double-storey building is already seven times stronger than it needs to be. However, given window and door openings and the fact that the gravitational forces need to be transferred around them, 1.3 MPa just covers it with a safety margin. It is important to grasp that it does not matter at all if you used clay bricks at 14 MPa, once something is strong enough, the extra strength means nothing at all.

Testing of the material

Tensile testing

–          Make a brick using the cob method (that is using sand, clay and straw ) and a 2 litre ice-cream tub as mould. Number each mix and mark your bricks and balls.

–          Allow the bricks to cure for 3 weeks minimum in the sun. A brick is considered cured after 3 months, but I have found that 3 weeks gives you a really good idea, after all it will only get stronger.

–          Drop the brick from waist height, onto a very hard and flat surface and observe how it breaks up. If it shatters it is no good; breaking into a few large pieces is acceptable. Often enough it does not break at all, which is fantastic.

A failed tensile strength test after being dropped on a hard surface; the brick should not disintegrate. Four big pieces is just a pass, but one is happiest when the brick bounces and does not break at all. This often happens.

A failed tensile strength test after being dropped on a hard surface; the brick should not disintegrate. Four big pieces is just a pass, but one is happiest when the brick bounces and does not break at all. This often happens.

Observe the cracking. Surface cracks, no deeper than a centimetre are fine. Cracks that run deeper compromise the material. They may be due to a very aggressive clay or because there is too much clay in the material. There can be other causes of the cracking such as the addition of too much water or uneven drying of the material.

Compressive testing

–          Make tennis ball size balls using the cob method and allow to cure, as above. A ball has a point and you are testing the point load. Remember to mark the balls.

–          Place the ball on a hard and flat surface. Stand on the ball with your heal and slowly increase your weight on the ball until all your weight is suspended on it.

My weight is around 80 kg and I know that if the ball crushes just before all my weight is suspended the MPa strength is 1.3. If it takes all my weight then the MPa strength is at least 1.4. As you gain more experience and your frame of reference increases you can quite accurately gauge greater MPa strengths by gently bouncing with your heal on the ball. At around 1.8 MPa the balls are very resistant to crushing with the heal, even with repeated bouncing; but then it does not matter because the material is already more than strong enough.

Both the compressive and tensile strength tests need to be passed for the material to be good enough to build with. Of course, if the material fails these tests it does not mean it can’t be used, especially if cracking is the result of failure. You can try excluding water and instead try ramming the material as a way of lining up the particles and see if that will works; or try making compressed earth bricks or even a sand-bag house?

Bottle, tongue and touch are all good indicators of how an earth is composed, but nothing beats compressive and tensile testing.

Bottle: place 4 cm of the earth in a 400ml bottle, add water and a teaspoon of salt to help it settle and shake it all up. It will give you an indication of the particle ranges you are dealing with and their ratios. However beware you will not be able to tell the difference between sand and silt.

To check if clay is present, make the material very wet and rub between your hands, then dip your hands in water, if the material sticks then there is clay present if it falls away then there is mostly or only silt.

Resistance to water erosion is dealt with separately in the plaster stage which will be dealt with later.

Below is a list of tests I made for Magic Mountains retreat as an example of a comprehensive earth test.

First walk the area you have to source your materials and then collect samples from various sites. Here I located 2 distinct earth types. White building sand was located close to the farm. Make observations of the material so you can begin to make rational choices for you mixes.

Earths ready for blending at Magic Mountains Retreat. Note the 2 litre ice-cream container for making a brick.

Earths ready for blending at Magic Mountains Retreat. Note the 2 litre ice-cream container for making a brick.

Red earth located in the South East corner of the property. This earth appears to have a high clay content. It is also attractive in colour. Made up of fine sand clay and unspecified amount of silt

Brown earth located to the North. This earth appears to have a higher sand content although very fine. Certainly has a lower clay content than the red earth.

White sand located to the South on a neighbours farm. This sand has a particle range that excludes finer particles and is angular and not rounded.

The following test samples were made to deduce the tensile and compressive strength of the material, clay content of the red earth, and cracking of the material will also be noted:

A100: 3 x 2l 100% earth bricks red earth and test balls

A100: 3 x 2l 100% earth bricks red earth with straw and test balls

3 x 300mm x 300mm x 170mm red earth bricks with straw

 

B100: 3 x 2l 100% earth bricks brown earth and test balls

B100: 3 x 2l 100% earth bricks brown earth with straw and test balls

3 x 300mm x 300mm x 170mm brown earth bricks with straw

 

50/50: 3 x 2l earth bricks 50%/50% red and brown earth and test balls

50/50: 3 x 2l earth bricks 50%/50% red and brown earth with straw and test balls

2 x 300mm x 300mm x 170mm 50%/50% red and brown earth bricks with straw

 

W80: 2 x 2l earth bricks 20% red earth 80% white sand and test balls

W66: 2x 2l earth bricks 33% red earth 66% white sand and test balls

W50: 2 x 2l earth bricks 50% red earth 50% white sand and test balls

 

C4:     2 x 2l earth bricks 50% red earth 50% sand and test balls

C66: 2 x 2l earth bricks 33% red earth 66% sand and test balls

 

2x compressed earth bricks from red earth

The completed bricks and balls should be left to cure in the sun for at least 3 weeks, and turned a few times to ensure even drying whilst keeping an eye on the weather.

The completed bricks and balls should be left to cure in the sun for at least 3 weeks, and turned a few times to ensure even drying whilst keeping an eye on the weather.

The bricks ready to be tested on a hard surface

The bricks ready to be tested on a hard surface

Results of the brick testing above

It was established that the red earth has a high clay content. Certainly above 60% as the bricks with 20% red earth and 80% white plaster sand were only just below minimum building strength. As soon as the ratio of red earth reached 33% it was obvious that the bricks passed both a compressive and a tensile strength test. It is estimated that the MPa strength at 33% is 1.4. Above 33% red earth and the bricks harden a lot.

The brown earth from below the dam could be used as a filler with the red earth, but this was decided against as it is in valuable agricultural land. It is not suitable on its own.

The addition of straw added to the tensile strength of the material in all cases.

The red earth bricks displayed deep cracks indicating a high clay content, once 50% sand was added the cracking was acceptable. The addition of sand will ensure that this does not happen and is a good enough reason to not use the red earth on its own.

The tests done with the white sand and red earth were strong enough from 33% red earth. A second test was also done with 50% red earth and 50% white sand which delivered a brick over 1.6 MPA.

 

Compressed earth bricks using red earth only, are strong enough and has no cracking. It is interesting to note that the red earth was suitable as a building material on its own if it were not for excessive cracking due to the swelling of the clay with water and that if one uses compression as a method of lining up the particles and so exclude water the earth can be used as it is.

It was decided that, because the white sand was easy to access with little environmental damage and because it would eliminate cracking, that the addition of 60% sand was the most favourable option; 40% red earth just to remain clear of the 33% mark that we know is good, in case the earth varies slightly. So 60% white sand and 40% red earth.

A series of tests made in Groot Marico. All these tests passed and although the red earth was most attractive it was decided to go with the brown earth as the red earth was further away and good for agriculture. The red earth was however used in the final plaster coat where the quantities are very small and not in the walls themselves. When a number of tests pass you are given the freedom to make choices around sustainability, and ease gathering the material when one compares them to each other.

A series of tests made in Groot Marico. All these tests passed and although the red earth was most attractive it was decided to go with the brown earth as the red earth was further away and good for agriculture. The red earth was however used in the final plaster coat where the quantities are very small and not in the walls themselves. When a number of tests pass you are given the freedom to make choices around sustainability, and ease gathering the material when one compares them to each other.

In conclusion, often when doing tests with different earths you will find that a number of your samples will pass both compressive and tensile test. This allows you the freedom to make choices affecting sustainability or aesthetics; such as how far the material has to travel, how easy is it to gather the material and what environmental damage is being done. Remember that you are not looking for the strongest sample but rather the one that makes the most sense after it has passed the tests. Strong enough is strong enough.

In my next blog post I will look at plastering of a building where the walls are able to resist the erosion of rain and the beauty of the material shines through.

Understanding Earth: The beginnings of a Natural Builder

By Peter McIntosh

One of the challenges of working with earth is that no two sites are the same. The recipes one learns on one site may not work on another, because the earths’ found there are composed differently. Most earth building relies on a mix of sand and clay, which may be present in a single earth or need to be blended together.

Sand has a particular particle size and is like a rock only smaller. You go from boulders to rocks to stones to gravel to sand to silt, or something like that. Each is a smaller representation of the one before it and just like you get many sizes of rock so you get a range of sand size. Sand particles range in size between 2mm and 0.0625mm which is a huge deviation.

The shape of sand in an ideal world should be shattered rather than rounded, such as beach sand. River sand is considered better because it tends to be more fractured so the sand particles do not slip past each other but rather build bridges and lock in together.

Ideally you also want the sand to have a range of particle sizes and not just lumped on the large side, 2mm or the small 0.06mm. This is because when the larger sand particles are packed together you will have spaces in-between and you want those gaps closed with smaller sand particles. Of course as you look closer you will see that there are spaces in-between the smaller particles and it really is like a fractal. The next range down is silt and ranges between 0.06 mm to 0.0039 mm, this particle would be able to close those gaps and so you go. So with sand you are looking for two things primarily, a shattered particle and a good distribution of particle sizes.

Clay is the magic that does the binding in earth building. Clay is completely different to what has been mentioned above except that there is some relation to particle size with silt. If you went to the beach and made a sand castle and then when it was dry a little pressure would flatten it, especially with those rounded particles. Do the same with clay and once it is dry it is immensely strong. This is because clay is not just a smaller sand particle but rather a flat platelet that is held together by electrostatic force. It works in a similar fashion to a drop of water between two pieces of glass, you can slide them apart but you can’t pull them apart. The trick with clay is to work the material until the particles are lined up to allow the electrostatic forces to work. There is always enough humidity in the air and retained in the clay to allow this process to continue, even in very dry conditions. Clay and silt are often found together in the same deposits and are hard to tell apart if they are mixed together. Mostly what is termed as a clay earth is a mixture with silt. I consider 60% a reasonable clay content . Clays also all behave differently. Some clays swell considerably when water is added and are great for the sealing of dams and the like but no good for building with cob or mud/adobe brick, as this leads to cracking in the drying process. Really fine clays also tend to be brittle, such as Kaolin, a fine white clay. So with clay you are looking for a nice high percentage with as little silt as possible, not too fine and one that does not swell to the point of compromising the strength of the material with excessive cracking once dry.

Now to create a building material both sand and clay are blended together, to get the benefits of the structure of the sand with the binding properties of clay. Basically you just want to add enough clay to coat the sand particles and close the last of the gaps left between them and allow the electrostatic force to hold it all together. You certainly do not want silt as that is competing for the space between the sand particles and is just where you want the clay to be. At around 18% there would be just enough clay to do the job. If there is silt present with the addition of 18% clay you would begin to force the sand particles apart and you would have a more brittle material, as the material is strongest when the sand acts as a bridge over each other, locking together.

But that’s the theory, in reality you are dealing with what is available and that is always going to be less than perfect. Your sand may have only large and small particles and nothing in between or any number of permutations, depending on how nature left its deposits. Your clay may be a mixed bag of various amounts of silt and swell in a less than perfect manner. So what you are looking for is not the ideal, that does not exist, but rather something that is suitable and strong enough for your needs.

Different methods can help with how the material behaves so choice of approach is important. Blending and lining up of the material can be done in essentially two ways both have their benefits and drawbacks. The first is to add water and mix the material until well blended to achieve a good lining up of the particles. Different methods allow for different quantities of water however the addition of too much water can lead to avoidable cracking or a material with less compressive strength. Cob is often the standard most people refer to and also has some added straw (straw adds to the insulation value and tensile strength of the material) The cob mix needs to be stiff enough to resist slumping when placed on a wall to the height of 300 to 500 mm. One of the benefits of using water is that different earth can be easily blended and straw can be added, a drawback may be that if the clay is aggressive or of a high overall percentage it could lead to cracking and a weakening of the material.

Adding clay to the sand on a tarp

Adding clay to the sand on a tarp

Add some water

Add some water

 

Mix cob with your feet and add some straw

Mix cob with your feet and add some straw

Stitching cob onto a wall

Stitching cob onto a wall

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The second method of lining up the particles is to put the material under pressure and not to add water beyond just slightly damp. The material can be stamped such as for rammed-earth or compressed such as with a compressed earth block. A benefit could be that as you are not adding water there will be less cracking even if the clay content is high and a drawback is that earths are not easily mixed together without water unless you have other machinery so a single earth is often used and the addition of straw is not possible.

Add your single earth into the compressed earth brick machine

Add your single earth into the compressed earth brick machine

Put the earth under pressure

Put the earth under pressure

Out pops a brick

Out pops a brick

Building with CEBs

Building with CEBs

Understanding how earth behaves is key to choosing a method of approach that supports the materials you have on hand.

In my next blog post I will talk about the qualities of earth what it means to say that a material is strong enough and how it performs (compressive and tensile strength, insulation and thermal mass) and how to test for these properties.

 

If you’re interested to learn how to put the theory of earth into practice, learn more about our natural building courses.

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Previous posts by Peter McIntosh:

Getting a feel for Light Earth

You might also enjoy: Using natural materials: a comparison, by Malcolm Worby