Announcing! The Green Building Academy 2018

We’re thrilled to announce Peter McIntosh will be co-facilitating Long Way Home’s inaugural Green Building Academy in Guatemala this year. Participants can expect a solid grounding and hands-on experience in green, sustainable building and construction practices, social development and a rich cultural immersion.  The Academy will take place in Comalapa, Guatemala, and will draw on the expertise of the Academy‘s instructors, who for 9 years have built an 18-building school using state-of-the-art green and sustainable technologies and methods.

The Green Building Academy provides a menu of unique educational options that are relevant to both professionals and students inside AND outside of the construction industry. Guided by best practices in green construction, the Academy is dedicated to educating individuals and organizations, in both theory and practical application, about sustainable design, planning, and building practices. Participants will connect to their environment, and develop increased consciousness & competence relating to sustainability, environmental & ecological balance, and ethical & respectful community development. The Academy equips participants with the knowledge, skills, and dispositions to apply their creativity to design and construction using sustainable, unconventional materials and low-impact methodologies with potential for off-grid implementation.

COURSE DETAILS: Continue reading

https://www.naturalbuildingcollective.com

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

Announcing natural building course dates for 2017

Are you on the track with your sustainability goals? Attend our natural building course this year and learn some essential practical skills to help you on your way to living the off-grid dream.

We are thrilled to announce that both courses will be held at Jakkalskloof bio-dynamic training farm in Swellendam this year.

Dates for 2017:

  • 19 – 25 March: Natural building course: materials and techniques (7 category 1 SACAP credits) ~ Jakkalskloof farm
  •  14 October: Natural building course: materials and techniques (7 category 1 SACAP credits) ~ Jakkalskloof farm

For more information please visit our course page or send us an email at naturalbuildingcollective@gmail.com to book your spot!

natural-building-course_poster_03_2017

https://www.naturalbuildingcollective.com

From the ground up ~ approaches to building a foundation for your natural building

When building with earth your foundation needs to be well considered as the integrity of your building rests here. Decisions you make about your foundation depend on the materials you have available, the type of ground you have to build on and what carbon footprint you want to leave. The goal should be to create foundations that are hard enough, move uniformly and resist cracking for the walls above it.

Foundations for conventional building have, to a large extent, a one size fits all approach regardless of the type of ground you are building on i.e. a concrete and steel foundation that works equally well on all types of earth and varies only slightly in its design. It requires little thought and has been proven to be effective. The cement in concrete provides the compressive strength, and the steel tensile strength to resist cracking. It does however come at a cost to both your pocket and the environment.

When building with earth your foundation needs to be well considered as the integrity of your building rests here. Decisions you make about your foundation depend on the materials you have available, the type of ground you have to build on and what carbon footprint you want to leave. The goal should be to create foundations that are hard enough, move uniformly and resist cracking for the walls above it. Foundations will always have a higher Mpa value than the walls, however it does not need to be excessive. A 4 Mpa foundation is sufficient for a 1.6 Mpa mud-brick wall, which most types of foundations are suitable for. Furthermore, if after levelling the site the undisturbed earth is hard enough, foundations may well be unnecessary.

There are several strategies for foundations depending on the type of ground that you are building on. In this blog post, I discuss the four types of ground, (1) uniformly hard, (2) uniformly soft, (3) hard and soft, and (4) clay, their challenges and several strategies you may incorporate into your design. The discussion is quite technical in some areas so I recommend that you read my three-part series on understanding earth first. Continue reading

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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

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

All good things must come to an end

… and 2014 is no different.

2014 course collage

It is with pride and joy that we look back on the successes and new connections made during 2014.
We launched our blog in March and have had over 5000 visits from people in 98 countries! The blog contributions included knowledge shared by our expert natural builder Peter McIntosh, to fly-on-the-wall takes of life as an architect and educator interested in building naturally and sustainably by Hermie Delport, personal lessons learned by owner-builder Laurie Simpson, and Amanda de Gouveia’s contributions as social development researcher at Qala Phelang Tala, a grassroots community upliftment and alternative building project focused on vulnerable communities in Bloemfontein. Other contributors included heritage consultant Lesley Freedman who about using indigenous earthen architectural knowledge, and green architect Malcolm Worby shared his thoughts on a comparison between natural materials.
Peter wrote a special piece for The Green Times, South Africa’s Green News Portal, on the relationship between building naturally and building sustainably; and our most popular posts this year on the blog has been his three part series on Understanding Earth, how to test earth, and how to make the appropriate decision with regard to plaster and mortar mixes.

Peter McIntosh facilitated three courses this past year: two CPD accredited courses at Magic Mountains in Barrydale, and one 6 day Natural Building: Materials and techniques course at Khula Dhamma in the Eastern Cape. All-in-all 33 people attended these three courses and got to do the mud dance and experience the art of natural building. Hopefully, that translates to at least 33 more natural buildings in South Africa!
Khula Dhamma reckons the course is a winner:

‘It’s hard work but huge amounts of fun, highly therapeutic and more rewarding than one could ever imagine. With the different techniques and materials and their thousands of capabilities, you are literally only limited by your own imagination and there is something so beautiful about that!’.. Read more.

If you want to see what other participants had to say about the courses please visit our updated Testimonials page. Or if you’re interested to see photos of the courses, you can either go to our albums on Facebook, or visit the Gallery page on the blog. Thanks to everyone who has liked, commented on, and shared our posts and events on Facebook! Our page has continued to grow, and we now have over 1200 likes, all thanks to you. If you’ve attended one of our courses, please note that we’ve now added the option to review us on Facebook.

Finally, Peter McIntosh has been part of an amazing project at the Lebone Village Arts and Culture Centre in Bloemfontein as one of the Mentors4Change. This collaboration with Qala Phelang Tala (Start Living Green) started on Mandela day, July 18th when Peter trained a few hundred people in the art of making mud bricks. Amanada de Gouveia wrote about the day here. Since then they have had a team consisting of volunteers and outpatients from the  University of the Free State’s Occupational Therapy clinic in Rocklands location, hard at work on the Shack Replacement project. This team was also privileged to attend the course at Khula Dhamma.
In recent weeks though, the focus has shifted to the Lebone Arts and Cultural Centre and the existing above ground cistern at the local orphanage. The crew includes volunteers, outpatients from the occupational therapy centre, a crew from Guatamalan NPO Los Técnicos (arguably world experts in alternative building practices [tyres, bottles bricks etc.]), and Peter McIntosh . Here you can see the progress from day one to day nine (photos courtesy of Los Tecnicos). For more photos of the building progress, please visit their Facebook album of the project.

The project is set to continue for another week or so, and hopefully they’ll get it all done in time. A great partnership has been fostered between these three organisations and holds great promise for other projects in 2015… Watch this space!

Finally, thank you to old friends and new for a blessed 2014. We’re looking forward to continue this muddy journey in 2015 as we explore new relationships and exciting new projects, more photos, knowledge and experience in how to build naturally and sustainably, to bring you, our supporters. We’ll be publishing our course dates for 2015 early in January so do keep an eye out for that if you missed out this year.

Thanks for joining us again, and we’ll connect with you sometime, somewhere soon…

Warm regards,
the Natural Building Collective

PS If you would like to get involved and write for us, be it a once-off, or more regular contribution, please send us an email with what you have in mind.

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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Breaking news: Six day course at Khula Dhamma, near East London 25 – 31 October 2014

I have been contracted to facilitate a six day course at Khula Dhamma, near East London at the end of October. This is in addition to the accredited course that I’m hosting at Magic Mountains retreat, near Barrydale in the Western Cape at the start of October. Both courses will cover the same basic topics, but you will be working with somewhat different materials. So if you can’t join us for one, maybe you can join us for the other course… Cobworkshop-KDRC

 

 

 

Contact Khula Dhamma directly at kdrc@khuladhamma.org to book for the course there.

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.

https://www.naturalbuildingcollective.com