A brief look ahead at our natural building courses for 2018

Attend our natural building course and take the first step to a sustainable future by learning hands-on natural building skills. Learn a whole range of materials and techniques while exploring questions around sustainable living based in Peter McIntosh’s experience living off-grid since 1999.

Natural building courses in South Africa 2018

If you’re serious about building naturally and sustainably then you’ll know that each technique has pros and cons. That is why our natural building course is designed around the principles of understanding earth, how it works and does not work together. You will leave with the theoretical understanding and practical grounding of a range of techniques and materials, so that you are able to make the most appropriate decisions regarding materials and or sustainability once you are ready to begin your project.

This year, Peter will be hosting two CPD accredited courses at Jakkalskloof farm, in Swellendam. Continue reading

https://www.naturalbuildingcollective.com

First natural building course of 2016

Announcing our first natural building course for 2016! Our natural building course is comprehensive and covers a range of materials and techniques based on Peter McIntosh’s professional and personal experience working with these approaches and from having lived off-grid since 1999.

The course will be taking place at Wild Spirit Backpacker’s in Nature’s valley from 17 – 23 April. You will leave with the theoretical understanding and practical grounding of a range of techniques and materials, so that you are able to make the most appropriate decisions regarding materials and or sustainability once you are ready to begin your project.

Drop us an email to book your place and avoid disappointment.

Poster 04_2016 sml

https://www.naturalbuildingcollective.com

TERRA Award ~ first international prize for contemporary earthen architecture

The TERRA award is a collaborative effort on an international scale to enable both professionals and the general public to fully appreciate earth’s increasing popularity as a building material of high aesthetic and technical quality. 

Earth is becoming increasingly popular in contemporary architecture: hundreds of projects of high aesthetic and technical quality are emerging across five continents. This material, which has low embodied energy, is readily available and appropriate for participatory buildings. It could help provide a solution to the needs for ecological and economical housing.

To enable both professionals and the general public to fully appreciate this building material, the following partners have taken the initiative, under the auspices of the UNESCO Chair “Earthen architecture, construction cultures and sustainable development”, to launch the first international prize for contemporary earthen architecture: the Labex AE & CC-CRAterre-ENSAG Lab research unit, the amàco project, the Grands Ateliers, the CRAterre association and EcologiK/EK magazine.

Wang Shu, 2012 Pritzker architecture prize laureate, is the president of honour of this TERRA Award, the trophies for which will be presented in Lyon on July 14, 2016 at the Terra 2016 World Congress.

Context

Since its creation in 1979, the CRAterre-ENSAG Lab has been considered as the international research and training reference centre for earthen construction. It will organize in July 2016, under the auspices of the UNESCO Chair “Earthen architecture”, the Terra 2016. This World Congress takes place every four years on a different continent and will be held for the second time in Europe. It is expected to draw around 800 professionals, teachers and researches to Lyon (France).

The TERRA Award was initiated within this framework. It will be the first international prize for contemporary earthen architecture and a natural furtherance of the national award launched in 2013 in France by CRAterre-ENSAG, AsTerre and EcologiK/EK magazine.

Objective

The purpose of the TERRA Award is not only to identify and distinguish outstanding projects, but also to highlight the audacity of the project owners for choosing to use earth, the creativity of the designers and the skills of the craftsmen and entrepreneurs.
An itinerant exhibition will feature 40 buildings from all continents, constructed using various techniques (adobe, cob, CEB, rammed earth, plaster, etc.) for all types of programs: housing, public facilities, activities, and exterior and interior designs. The exhibition will be completed with lectures and workshops by CRAterre-ENSAG and the amàco project.
The search for outstanding achievements deserving of this prize and the associated exhibition will make it possible to generate the first worldwide database on contemporary earthen architecture. The resulting virtual library will be available both to the general public and professionals via this website.

Involved projects

The projects must have been completed after January 2000.
There are eight categories covering all types of programs, whether new or renovated:

  • Individual housing
  • Collective housing
  • School, sports and health facilities
  • Cultural facilities and religious buildings
  • Offices, shops and factories
  • Interior layout and design
  • Exterior design, art and landscape
  • Architecture and local development

Text from the Terra Award website.

https://www.naturalbuildingcollective.com

Owner-builder journey ~ Franz Muhl: Energy flows where attention goes

In this edition of the Owner-builder journey, Franz Muhl writes about a mud brick addition to his Scarborough home: “Let me build a home from fertile materials that is beautiful and healthy to live in, have a very low footprint and would grow a forest if you left it.”

Franz 1

Five years ago, Peter McIntosh gave me +- 900 sun-baked mud bricks, for an extension to my house. Franz 3With little start up money, a trickle of income, some plans on google sketch up, a pickaxe and, most importantly, plenty of time, I finally started the process a year ago.

 

At foundation level, with the skills that I had at the time, I used clay-fired bricks and a bitumen coat for damp-proofing. Franz 4In March, I headed off to Berg-en-dal for a crash course with Peter. He traded his skills and knowledge in natural building for mine in brewing beer. To take clay, sand, water and a bit of straw in the right proportions and work it into a material for building, was a big revelation for me. Continue reading

https://www.naturalbuildingcollective.com

CPD accredited natural building course: Materials and techniques

Our natural building course is comprehensive and covers a range of materials and techniques based on Peter McIntosh’s professional and personal experience working with these approaches and from having lived off-grid since 1999. You will be empowered to be successful and make rational choices whatever the given situation.

We’re excited to announce the first course of the year will be taking place from 26 April – 2 May, at Wild Spirit Backpacker’s lodge in the beautiful Nature’s Valley.

Take the first step to a sustainable future by learning hands-on natural building skills. Understand the alchemy of how different types of earth work, and do not work together, their potential and limitations. You will also explore questions around sustainable living based in Peter McIntosh’s experience living off-grid since 1999.

Email naturalbuildingcollective@gmail.com to book your spot!

CPD accredited Natural Building 7 day course_April_WS

 

 

https://www.naturalbuildingcollective.com

Understanding earth III: Plaster and mortars mixes

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

Plasters and mortars are by far the process that I get asked about the most, and for good reason as plasters are what protect the building from the elements and give them their beautiful finish. Understanding how the material is going to behave right the way through the process, plasters and mortars should be planned for from the beginning. Plasters that are not planned are plasters that fail and if they do the building not only looks unsightly but loses a valuable layer of protection.

As discussed in the earlier articles on understanding earth and earth testing, it is important to establish the most appropriate earth mix at the beginning of the building process. This mix quite literally informs the whole building process from the ground up to the last 3mm of plastering. The initial testing phase establishes a basic cob mix that has both sufficient compressive and tensile strength and has acceptably low cracking. It is important to have an idea of how you will approach each phase and ensure that the different materials ‘talk to one another’ to prevent excessive cracking and delamination, which are the most common failures associated with natural building. Essentially the same original mix is manipulated to be appropriate for different areas, depending on the purpose. Areas that will require the original mix to be manipulated are, amongst others, the foundations and plasters.

It is important to remember that there are as many mixes as there are building sites and what follows is just a taste of what is possible. Over the years one comes to settle on a strategy that works and begins to perfect it to prevent failure. What follows works, but is by no means the only way and is one amongst many.

Let us imagine that the mix you worked out after the testing phase was two parts clay and three parts sand, i.e. 40% clay earth and 60% rough sand, and straw. Just an aside, this formula would indicate that there is a percentage of silt present in the clay earth (often the case), otherwise the clay percentage would usually be lower.

Let’s start with a mortar mix for the foundations. Firstly you will leave straw out of the mortar mix for the foundation, as it would degrade with any moisture. Obviously the foundation should be able to resist water, so using un-stabilized mud-bricks or cob is not possible; ideally you have rock available.

Lime is often seen as the answer to stabilise mortar mixes, as it hardens over time especially when exposed to moisture. However, lime is not friendly to the environment due to the high embodied energy i.e. the energy used to create the product. Over time lime does re-absorb the gasses given off by it during its production, the energy required in this phase is considerable and may well come from a polluting source such as coal. Furthermore, lime is quarried or produced by crushing coral. Lime also makes the material more brittle and prone to cracking, even though the material gets a lot harder, compressive strength is not everything. Often, lime is considered to be better than cement, not because it is less damaging to the environment, but rather because it is naturally occurring and an ingredient of cement. So the strategy should be to minimize its use.

Earth mixes are more plastic and able to resist a certain amount of movement so care needs to be taken just where you apply the lime. However the use of lime is beneficial in foundations where the pros of lime, its hardness and resistance to moisture, are required. With the earths in our example, a mortar mix that will work with the rock foundation is 30% clay, 50% sand and 20% lime. This keeps the material as close as possible to the original mix while getting the benefits of the lime right where you need it. If you pay attention to how the rock work is done you will minimize the use of the mortar and thus minimize the use of lime.

As your house is exposed to variances in temperature and humidity, you want to prevent the materials in the walls from moving at different rates as it causes delamination and cracking, which is in my opinion, the number one reason for a natural building failing. To help prevent this you need a good mortar mix. This is an area that your mix does not need to be manipulated. Between your mud bricks it is ideal if you stick to the original mix that came directly out of the testing phase, including straw.

While some imperfections are fine in the foundations and mortar mixes, any imperfection in your plaster mix will have dire consequences for you final finish. This is mainly because there is generally no amount of acceptable cracking in the final plaster as this leaves the building vulnerable to water erosion. In a nutshell, plaster provides the final finish look and provides protection from the elements.

I have adopted a three phase approach to plastering that is well accepted and works. The first is the scratch coat, the second the form coat and lastly the final plaster coat. The scratch coat is your original cob mix applied to the mud bricks to give purchase to the subsequent layers. It includes straw and is left rough often with lots of fingertip marks.

Scratch coat on this straw bale building near Groot Marico includes more straw and is left rough and textured.

Scratch coat on this straw bale building near Groot Marico includes more straw and is left rough and textured.

The form coat is just what it says and creates the final shape of the building. At this stage it is best to leave out the straw as you don’t want anything protruding through your final plaster coat. The form coat is hand smoothed in such a way that the final plaster coat can go on evenly with a plastering trowel or steel float. Fine cracking is still acceptable in this phase.

On this mud brick building in Scarborough near Cape Point, you can see the scratch coat on the left, while on the right the form coat cob mix, excluding straw, is being hand smoothed.

On this mud brick building in Scarborough near Cape Point, you can see the scratch coat on the left, while on the right the form coat cob mix, excluding straw, is being hand smoothed.

Prior to the final plaster you will need to do a number of tests on top of your form coat. This is done to ensure that there are no fine cracks that will lead to erosion by water. Often cracks create wonderful patterns and you may want to leave the mix to show off its beauty but only on the inside plaster. On the outside no cracking is acceptable after the material has been polished. Usually I do about four tests to select the best mix. Based on our theoretical mix for this article the four tests may look something like this.

  1. First your original mix, 40% clay, 60% sand with 5 % lime =105%
  2. Second reduce the clay a little to reduce potential cracking 35 % clay earth, 65 % sand plus 5% lime.
  3. Reduce the clay some more just in case there is still cracking to 30 % clay earth, 70 % sand plus 5 % lime.
  4. Lastly increase the clay content over the original mix, 45% clay earth, 55% sand plus 5% lime.

    The walls were still going up when we started the Final plaster test patches for this compressed earth brick (CEB) building in Scarborough, Cape Point, SA.

    The walls were still going up when we started the Final plaster test patches for this compressed earth brick (CEB) building in Scarborough, Cape Point, SA.

As these samples are applied so thin they will dry fast so decisions can be made fairly quickly, perhaps after three days or so. You will need to choose the mix that does not crack. If it so happens that none of them do, pick the one closest to your original mix to ensure that the dreaded delamination is ruled out. If you are confident that this will not happen then choosing the mix with the highest clay content will lead to a very fine finish.

Technique is as important as information when it comes to natural building and nowhere is that more important than with the final plaster mix. The final plaster mix needs to go on evenly between 3 and 5 mm thick. The mix changes slightly to include 5 % lime, but only in these last few millimetres. The reason lime is added to this final 3mm – 5mm of the walls is to improve the resistance of the final plaster to water; the percentage is kept low so that the material does not become brittle and prone to cracking, and allows the natural plasticity of earth mixes to overcome small amounts of movement and not delaminate from the wall. There is also a reaction that takes place between the lime and clay that is complete between 5 and 7 %, which greatly increases its durability.

The final plaster mix will need to be finely sieved so that bigger particles do not protrude through the plaster and the result is smooth and even. I prefer the common kitchen flour sieve. Don’t be put off, by how long you think it would take, because you really need so little for the final plaster mix that it goes quite quickly and you can do it directly into a bucket.

Here the final plaster coat is being applied to the exterior of the straw bale building near Groot Marico. It’s between 3mm and 5mm with 5% lime and polished.

Here the final plaster coat is being applied to the exterior of the straw bale building near Groot Marico. It’s between 3mm and 5mm with 5% lime and polished.

Once the final plaster is applied it is polished to provide a very smooth almost fine leathery appearance, further driving the material into the wall and providing durable weather protection. A plastic tool cut from feta or ice-cream tubs work well for this final polishing stage.

Once the plastering is complete, coat the building with three coats of raw linseed oil. Mix the first two 50/50 with mineral turpentine to ensure that the linseed oil penetrates well into the plaster. Allow each layer to dry before you apply the next. Finally a coat of undiluted raw linseed oil will finish it off.

Looking at the whole process as being one thing instead of being separate little bits helps to avoid common problems. Always pay attention to the testing phase, understanding that the same mixes you use for your bricks and mortars will be reflected in your foundations and plasters.

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New directions in informal settlement upgrading and community-led sustainable building practices – The Freedom Square shack replacement project – Day 18 (Thursday 2 Oct’14)

I came to learn how to build a cob wall; instead I learned the story of my life before I even stepped onto the building site.

It was day 18 at the Freedom Square shack replacement building site in Bloemfontein, but my first day on the premises. The walls of Lientjie’s new house were already about three quarters completed. The first one and a half meters from the floor up was made of compounded tyres and solid cob packed firmly into and onto a reinforced metal grid. From this solid section of wall up toward the beams, the building team has started to experiment with decorative wall building techniques such as inserting colored glass bottles in patterns into the cob and carving edgings onto the walls. The total effect is of a mud wall inserted with an array of miniature skylights. It was still early morning and the sun spilled through the little skylights in mesmerizing colour.

So how does one build a cob wall? In an ideal world it would be with a rigorously tested cob mix of course. However, in this part of Freedom Square location life is hardly ideal. Here lives the abject economic disadvantaged and marginalized, those whose only option is to make do with what they have. Even the earth lacks succor and consists of 70% clay. The Qala Phelang Tala building team, as change agent and mentor, has therefore devised a method of ensuring an optimal cob mix, by mixing in a ratio of dry horse dung and fine sand.

By now each member of the regular building team has established their niche. While Ellen Maphalane and Tiisettso Chobokoane were making bottle bricks, Abraham Nkotywa was layering the wall with cob mix and finished bottle bricks. Mokoena Maphalane carried buckets of clay, horse dung, sand and water to the mixing area and all stomped the cob mix together. Tiisetso two year old niece, Pimelo, was following suit and industriously heaving water back and forth in her small porridge bowl. Anita was decorating the cob walls with her carvings while Oretile, the little boy from across the street, was avidly watching her every move. He was totally engrossed by Anita’s unique skill and the beautiful wall art that she was creating.

1.Tiisetso showing the Occupational Therapy students the finer art of refining details on the wall.

Tiisetso showing the Occupational Therapy students the finer art of refining details on the wall.

Each member of this seemingly ragamuffin building team has his/her own story of hardship and grief, adversity and woe. Abraham is 62 and has suffered from cancer, interspersed with periods of remission, throughout is life. His four children all passed away young, two as babies and two during toddlerhood. His wife also passed away of cancer. Two years ago, during a particularly robust bout of full blown cancer, he prepared himself for dying and bequeathed his house to his brother. Abraham survived the cancer, but found himself homeless upon finally being released from the hospital. He now lives in a tiny, battered shack at the back of his brother’s house, the house that once belonged to Abraham and that he had given to his brother. Abraham used to be a builder and his natural skill is evident in the perfect symmetry of the wall that he is busy building, his bare hands the only tools of his trade.

Mokoena is only 28, but was born with a heart defect. He suffered a stroke at 26 and is now partially impaired on the left side of his body. Mokoena, physically supported by his mother, Ellen, walks 5km every morning from their shack on the other side of Freedom Square location to the building site. For Mokoena life has gained new meaning since he started participating in the building activities. He spent his childhood on the periphery of normal youthful activity. As a result of his weak heart, he could never participate in games and sports with his friends and school mates. Now he is in the thick of things, actively contributing hard labour toward building a house for a fellow community member, while at the same time learning the skills that will enable him to one day built his own house for himself and his mother.

Waldo and Hugo joining building activities in the school holidays; here Mokoena and Abram show them the 'seretse jive' (mud dance).

Waldo and Hugo joining building activities in the school holidays; here Mokoena and Abram show them the ‘seretse jive’ (mud dance).

Abraham and Mokoena both came to be a part of the Qala Phelang Tala building mentorship programme as a result of being out-patients at the University of the Free State’s Occupational Therapy clinic in Rocklands location. Their presence is testimony to the effort and dedication of Heidi Morgan and Bronwyn Kemp to reintroduce their patients back into their communities as fully functional members, able to contribute towards and participate in living a full life.

As for the humble story of my life – well, I was standing in the doorway of Lientjie’s existing shack dwelling and hesitantly introduced myself to the three adolescents inside. They courteously reciprocated and introduced themselves as   Thembeke (18), Lonkululeko (16) and Kenneth (15) and invited me in. We chatted tentatively for a while and I asked about the beads they were wearing. It turns out that they are a trio of aspiring sangomas. The calling from the ancestors runs in their family and each one of their lives is currently a conundrum of figuring out how to heed their calling, appease the ancestors, while still having a normal adolescent life and attend to school and studies. After about an hour or so Kenneth produced a small, vibrantly patterned bag and benevolently offered to throw the bones for me. I cautiously obliged. He asked me to blow three times into the bag. A short ritual ensued of shaking the bag, repeating my name and singing softly. He emptied the little bag on the floor in front of me.

The Freedom Square Shack Replacement crew on site, day 18.

The Freedom Square Shack Replacement crew on site, day 18.

I could not help but be transfixed by the contents that now lay scattered at my feet. Among the bones, shells, beads and trinkets lay four large steel nails. The first thing I noticed was that they all lay with their sharp ends facing away from me. I remember thinking: “that must be a good thing!”. According to my trio of hosts, this was indeed the case. It meant that there are no people in my life who actively wished me harm. As for the rest of the story told by the bones – all I am prepared to say is that it cut disconcertingly close to the bone. However, I somehow doubt that I will consent to having the bones thrown for me again. The prospect of those nails potentially facing me with their sharp ends next time is too dreadful to contemplate. Quit while ahead, me thinks…

Contributed by Amanda de Gouveia on behalf of QPT. Photos courtesy of QPT. Please visit their Facebook page for more photos of the day.

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Amanda de GouveiaAmanda de Gouveia has been a research assistant at the Centre for Development Support at the University of the Free State since 2010, where she has mostly been involved in research projects on social development and local economic development. This has refined a unique repertoire of research skills, both qualitative and quantitative. She has also Masters degree in Research Psychology.

https://www.naturalbuildingcollective.com

Lebone Village launch

Imagine being outside on a chilly Free State winter morning with the sun just coming out and starting to gently warm your body. Now imagine being told to take off your shoes in order to trudge in icy cold mud. I glanced at my fellow volunteers and I saw a collective dissent quietly dawn on our group – this is not what we signed up for!

Mandela day

It was the morning of 18 July, Mandela Day, and we were all gathered at Lebone Village on the outskirts of Bloemfontein to volunteer our 67 minutes for the orphans. We were standing in a circle around Peter McIntosh, who was valiantly demonstrating to us the endeavor of making adobe bricks.

Peter McIntosh demonstrating how to make cob

Peter McIntosh demonstrating how to make cob

The mix using ingredients easily available for the project was chosen after rigorous testing. According to Peter, the mix will differ in every situation, depending on the composition of the ingredients used. The chosen mix for the adobe bricks at Lebone Village was as follows: collect two parts red earth, 2 parts sand with rubble, one part fine sand and two parts water in the centre of large piece of 25” thick canvas material.

Now mix it all into clay with your feet by walking back and forth through the cold, wet mixture. When the cob mixture starts to flatten out, pull the canvas up-and-in towards you from the corners to bring the clay mixture back into the centre of the canvas and into a manageable heap. Now start stepping onto it again. The clay is the right consistency when you can make a ball with your hands and pull it apart into two separate pieces without it crumbling. Adding straw to the mud mixture assures bricks that are well insulated against cold and heat, the more straw you add, the better insulated your bricks.

Adding water

Adding water

Adding straw binds everything together and adds insulation value

Adding straw adds insulation value

Lots of people turned up

Lots of people turned up

 

While the majority of us were still apprehensively contemplating the prospect of braving the cold and mud with naked feet, one person rose to the occasion without hesitation. In the spirit of “first being a follower in order to be a leader”, Itumeleng Santo started pounding the mud into clay with some über cool dance moves. Itumeleng is an out-patient at the University of the Free State’s Dept of Occupational Therapy’s clinic at the MUCPP offices in Rocklands location. He is severely impaired due to a brain injury that he suffered during an assault. For Itumeling, taking part in the Mandela Day activities at Lebone Village was therefore also a day of getting therapy without being given therapy. The Dept of Occupational Therapy vision is to support and treat their disabled and impaired patients in such a way that they will be able to return to their families and communities and be able to fully participate in community activities again. The aim is for such patients to become fully functional individuals who can partake in economic activity and contribute towards their own livelihoods.

The MUCPP clinic of the Dept of Occupational Therapy is not only for patient care and therapy, but it also serves the wider community as a place where youth can hang around after school and in this way be kept off the streets. Heidi Morgan and Bronwyn Kemp, who run the clinic, aspire to teach these children skills that will help them to create their own employment upon completing their school careers. Learning how to make adobe bricks and tire pounding for alternative and natural building practices are two such skills.

This notion of self-empowerment of the impaired, disabled and destitute was the golden thread that ran through the activities at Lebone Village on the morning of Mandela Day. Stakeholders from support institutions to the disabled came from all over the Free State region to learn the new green building techniques of making adobe bricks and pounding tires. These are skills that they intend to take back to their home towns and villages, skills that they hope will enable them to become self-sufficient and self-employed, able to earn money and make a living for themselves, without being a burden to their families.

Getting our feet dirty

Getting our feet dirty

Peter McIntosh demonstrating putting cob into the brick mold

Peter McIntosh demonstrating putting cob into the brick mold

With the ice now literally and figuratively broken by Itumeleng, the rest of us started to get into the spirit of the day. The extra brave ones took of their shoes and started pounding cob with their bare feet. The more modest traded their shoes for gumboots to get the job done.

Some started working the cob with their hands. Anita put on some vibey music and soon the day was in full swing. Volunteers started forming little groups, each group working their cob on their own piece of canvas. Some people would collect the pounded cob and compact it into wooden molds set out by Peter for this purpose. These mudbricks would then be left to dry in the sun for several days, where after they will be ready to use for building.

Peter McIntosh demonstrating putting cob into the brick mold

Peter McIntosh demonstrating putting cob into the brick mold

The teaching of green building techniques to the greater Mangaung community also served as the launch of the Lebone Village Climate Resilient Arts, Crafts and Cultural Hub and was initiated by Qala Phelang Tala, a non-profit organization based in Bloemfontein and associated with the Centre for Development Support at the University of the Free State. Qala Phelang Tala is Sesotho for “Start Living Green” and is the brain child of Anita Venter, a researcher at the Centre for Development Support. QPT strives to empower “change agents” through social entrepreneurship in order to create systems addressing housing, food security, water efficiency and energy independence that are resilient to climate change. Their slogan is “Learn by doing!” This means that they not only preach green building and sustainable, environmental friendly living, but they also practice, implement and teach these techniques. QPT head hunted and hosted Peter McIntosh from Natural Building Collective, who is one of only a handful of natural building experts in South Africa. His experience in sustainable living practices includes sustainable agriculture, off-grid energy systems and an array of natural building techniques, all of which is in fruition on Berg-en-Dal outside Ladismith in the Klein Karoo, a farm owned and managed by the community and educational non-profit the Klein Karoo Sustainable Drylands Permaculture Project, where he is a resident and member.

Some of the mudbricks that were made on the day drying in the sun

Some of the mudbricks that were made on the day drying in the sun

Contributed by Amanda de Gouveia on behalf of QPT. Photos courtesy of QPT. Please visit their Facebook page for more photos of the day.

Amanda de Gouveia

Amanda de Gouveia has been a research assistant at the Centre for Development Support at the University of the Free State since 2010, where she has mostly been involved in research projects on social development and local economic development. This has refined a unique repertoire of research skills, both qualitative and quantitative. She has also Masters degree in Research Psychology.

 

 

https://www.naturalbuildingcollective.com

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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https://www.naturalbuildingcollective.com

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.

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