Friday, November 26, 2010

The Rammed-Earth House by Anthony F. Merrill

I recently re-acquired another copy of Anthony Merrill's The Rammed-Earth House  and thought I'd better scan it before I lost this one to another scoundrel.

Here are a few illustrations from this long out-of-print tome.  This winter we'll scan the chapters and post the pages on flickr.

Friday, October 01, 2010

Some Year Old Papers Related to Rammed Earth

While I was poking around for information related to John Cheah's work on Maori rammed earth housing, I found a couple more articles from the proceedings of the 11th International Conference on Non-conventional Materials and Technologies (NOCMAT 2009) that relate to our purview here at REi4E.

There's ACHIEVING CARBON NEUTRAL STRUCTURES THROUGH PURE TENSION: USING A FABRIC FORMWORK TO CONSTRUCT RAMMED EARTH COLUMNS AND WALLS by Alan Chandler and Rowland Keable which has not-to-be-missed photos of the world's first rammed earth mattresses


ASSESSING THE ANISOTROPY OF RAMMED EARTH by Quoc-Bao Bui and Jean-Claude Morel which attempts to settle a controversy at the heart of many fights between rival factions of engineers: Is rammed earth isotropic or not?

I can hardly wait to read the proceedings of 2010!

Thursday, September 30, 2010

Q & A with John Cheah of the University of Auckland

I am very grateful to Mr. Cheah for taking time to share his information with this blog. 

If you'd like to keep up with more earth construction news in New Zealand , be sure to subscribe to the Earth Building Association of N Z newsletter.



What kind of forming system do you use? Any pitfalls or improvements?
We build modular rammed earth panels. This allows us to build walls up to 2.2 meters long and at variable thickness from about 350mm to 150mm. The height of walls that we can ram is limited to 2.4 meters. I've attached a photo of the original red formwork. This formwork is designed to be very flexible in terms of wall thickness.

We have since designed a complimentary set of black formwork with less flexibility (best for ramming 200 mm thick walls) which is about a fifth or less of the weight of the red forms and much easier to set up.We use both and have a few more ideas of how to make it easier to build certain difficult geometries including T sections and L sections.

There aren't really any pitfalls with this system that I've found so far. Single standalone walls are very easy to build using this modular formwork. Because we reuse the formwork we only need enough formwork for one panel to build a house. Building joining walls is a little more complex but with familiarity and experience should take the same amount of time to take down from the previous wall and set up for the next (which is about 45 minutes). Making sure everything is wedged up tight and level is important and prevents issues arising later on.

We sometimes put a strop around the whole system to add stability and safety (in the place of a guard rail at higher heights). The speed at which we have been ramming the Ahipara house has been about 5 panels a week. We can build 2 wall panels a day but it is very physical work so we aimed to do one wall a day and spend the rest of the day preparing for the next day and resting. A 2m long, full height wall takes about 3-4 hours to ram with a 6 person team.

We needed 6 people because we decided to do the Ahipara house without a bobcat and had a large archimedian screw sort of machine instead.

We would typically have:
- 1 person mixing in the right amount and proportion of sand and clay in the screw drive
- 1 person mixing in the right amount of NZ Flax fibres and cement in the screw drive
- 1 person looking after the water addition in the screw drive, making sure it's about right and ensuring everything is getting mixed well (quality control)
- 1 person transporting the mixed soil to the wall panel being rammed (also does some quality control)
- 2 people on the formwork ramming - alternating with the hand rammer and the pneumatic rammer.

What type of footing/foundation?
We have a reinforced concrete foundation around the perimeter of the rammed earth walls/house. The floor in Ahipara will be of stabilised rammed earth - the same as is used for the walls.
It should be noted that for each structural wall panel, there were two D16 vertical reinforcing bars placed 150mm from both edges of the wall panel.

How did you finish the top of the walls and attach your roof? 

Top of wall panels have a reinforced concrete ring beam into which the vertical reinforcing going through the wall panels was bent into. In NZ we have to design for seismic loads and this is the reason why we have steel in our walls and a reinforced concrete bond beam.

How did you attach your doors and windows?
We embedded pieces of wood into the edges of the wall panels when ramming which could later be screwed into.
In Ahipara we rammed the wall panels next to doors and windows flat (with no embedded wood) and will fix a thin piece of timber to the wall panels next to openings and then fix the doors and windows onto those pieces of wood.

What type of construction equipment did you use?
We have used bobcats in the past. For the Ahipara project we decided to use the screw drive. Interestingly we found near the end of the project that hand mixing worked quite well and was fast - but tiring. After working on site for a while though, the guys I were working with were more fit and are generally big and strong so this worked well.
We used one pneumatic rammer and one hand rammer.

How long did it take to build the walls?
There were about 28 walls in the house - this included short walls, window walls and non structural walls. In terms of ramming days it took about 25 days as we were able to build two walls in one day on several occasions. In terms of time, we built the first wall on 23rd April, 2010. We built the last wall on the 17th of June. Once we had reached the physical construction stage, delays took the form of gathering resources, rain, family and community events (including trying to save and then later euthanising a beached pilot whale), occasional disputes and equipment failure.
The Ahipara uku walls are 200mm thick and the Rotoiti UKU walls are 150mm thick.

Any horizontal re-bar? I am surprised at how little reinforcement you are using considering your seismic zone 

No. We have done lots of testing at a small level and at full size in the labs and on the field and did a specific design for the house.

We are fortunate that Ahipara (in the far North of New Zealand) is in the lowest seismic zone in New Zealand. I'm currently doing shear tests in the UK to better understand the shear performance and characterisation of earth so we can more confidently design in more earthquake prone areas.

No concerns regarding moisture ingress with flax fibres?
The flax fibres are a naturally abundant resource in many areas of New Zealand. We include them for:
- cultural reasons - traditional use of flax fibres in many aspects of lifestyle however not in it's current function as reinforcement for rammed earth walls.
- It does improve the thermal insulative properties significantly albeit from quite a low base so it is not significant enough to be a reason to include it just for thermal advantages.
- It increases the tensile strength of the material so cracks form under larger forces and after cracks haved formed the material has a much larger residual strength instead of being prone to cracking further with no reliable strength.
- It reduces shrinkage in the walls and increases volume stability.
- It helps with durability - it acts as a kind of stabiliser binding everything together - in parallel with the compaction and cement and clay actions.
- I am currently doing research on the shear performance and seeing what benefit there is on that property and to what extent. Shear strength is important particularly in earthquake prone areas of which NZ is one.
The cement stabilised walls are more susceptible to long period of exposed water. E.g. through a wet winter and no sun to dry the walls we have had one instance of water getting through the wall. The fibres do not seem to be creating any issues with moisture. Eaves are important and the Ahipara house will likely have eaves out to 2 meters. Sun exposure is also very important.

Are the houses plastered inside and out?

No plastering inside or out.

How did you determine your soil mix?
Soil mix follows commonly accepted limits for rammed earth construction. I use Houben and Guillaud's recommendations. The sand content is around 60%, clay between 10-15%, silts and gravels vary in between this. We do use  around 7.5% portland cement I also do quite a number of other tests included Atterberg limits tests to find the liquid limit and plastic limit and a Proctor Density Compaction test and shrinkage box tests. As a research student at university it is much easier for me to do these tests and there would be considerable cost to get these tests done in New Zealand using an independant testing laboratory.
We have mainly used two different soils so far. The compressive strengths do vary quite a bit but our soil strength must be at least 1.3 MPa to be acceptable for structural use and we have measured strengths up to an average compressive strength of 7.5 MPa. 

Are you concerned about variability in your mixes?
This is more an experience and a process and quality control issue. We minimize variability as much as we can. We got quite consistently high quality mixes and wall panels throughout the project. If any panel was poorly rammed we knock it down. We did it once on the Ahipara project. Due to the large conservatism built into the mix design and house design a bit of mix variation was not a concern. For me, the use of cement was helpful in this sense as it does give a reliable base level material performance. We were using people from the community that were inexperienced initially in earth building and were building in a largely variable climate (hot and sunny / scorching, very windy, and sometimes ramming in heavy rain). Looking at the finished house I am happy with the result and quality.

How many houses have been built since the start of the project?
We have built 4 UKU structures. The first two were single room dwellings, built in 2004.  The first house was built in Rotoiti, the next in Ahipara.

What has been learned with each successive build?

Many things! We've been extensively monitoring the first UKU house thermally and with 150mm thick walls in a area that went down to -7 C in 2009, it performed really well. We've learnt a lot from a construction and practical perspective.

I've personally learned a lot about dealing with council and the engineering design side of the project. The project has been quite a holistic one and I have enjoyed it all the more because of this. Strangely, although it takes more time to get to know the community I'm working with, things actually happen quicker because after a decision is made, everyone knows what is happening and people and resources come together just when we need it.

It requires a little bit of faith and a good portion of optimism but they're rich in resources and expertise up there, and very resourceful such that we have rarely been delayed because of materials and labour. It's actually been council and gaining council consent that created the most issues for us (and this is on-going). Still, we are building bridges with them also and plan to build more of these earth houses in the near future. The second house should be much smoother to work through council as they will be more familiar with the building technique and we will be more familiar with what they want to see and know.

Working in rural Maori communities also has many different dynamics that need to be understood and that can greatly benefit the project. Including things like following their ancient calendar called Maramataka. This specifies that there are good days to work, and bad days to work, days to rest - not based on 7 day week. So we won't have a meeting with council on a particular simply because the maramataka is bad.

The house construction also followed traditional Maori tikanga/protocols and one of those is that females are not allowed on the work site until it is completed. A female walking on site would traditionally be part of the officiating/commissioning process. Heeni, the wife, and a few other female friends and relatives did help out with some of the flax fibre processing and were allowed on site to have a look after hours. All the physical construction was done by males. Heeni did a lot of work on raising sponsorship, community awareness, dealing with council, general communication, keeping track of project, media control, resources and funding.

Maori have such an impressive carving culture, it would be wonderful to see these designs transferred to walls, especially if there are standardized housing plans in practice. Any experimentation with artistic techniques? 
Not yet - although we have managed to get beautiful impressions from the plywood formwork. I have thought about it and several people working on the project and visiting the project have asked about this. I can definitely see this is a valuable thing to explore. Earth walls are built from the soil their ancestors lived on and that provided for them so it is very valuable and meaningful  (and beautiful) already but with some art / symbols in them would become so much more valuable.

Do the houses have a heating system?
Rotoiti was meant to have a wet back fire place but it hasn't yet been installed. They used a gas heater through the worst of winter. Generally speaking the energy usage was still very low.

I was impressed by the community's insistence on houses that last six generations
On this point - Maori are connected with their land. They have no intention of moving or selling. Everything is inherited by their children. They don't actually see themselves as owning the land either. They are guardians, this is their role and responsibility. Houses that last 6 generations was decided as a good target lifespan to towards which to work.

Tuesday, September 28, 2010

Excellent Paper On Historic Rammed Earth in Alabama and the US

A Masters Final Project submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Master in Historic Preservation, 2010

Ms. Carpenter has put many great sources together to discuss the seven rammed earth homes built by the US federal government during the New Deal.

Lots of contemporary photos of the houses as well as documentation of the construction process. Historic context underscores the importance of these dwellings and their preservation.

Monday, September 27, 2010

Rammed Earth in Aotearoa / New Zealand

UKU is a research project which is focused in the immediate sense on developing an appropriate housing solution for rural Māori communities, but in the longer term on affordable, appropriate construction technologies for third world countries. At present a large proportion of rural Maori are living in sub-standard and overcrowded living conditions. Conventional housing solutions are not appropriate for many rural Maori communities due to the financial aspects (cost, maintenance issues), practical issues (transport of materials, isolated location, lack of infrastructure) and legal issues (multiply owned land and Maori land title).

In 1994 the UKU concept was conceived by Dr Kepa Morgan of Ngāti Pikiao to build houses using flax-fibre reinforced earth. Through the support and involvement of research organisations and businesses like Ngā Pae o te Māramatanga, the Foundation for Research Science and Technology, Te Runanga O Ngāti Pikiao, the Forest Research Institute, the University of Auckland, Golden Bay Cement and Pacific Steel, the UKU project has developed and refined the UKU building method, identified optimum mixtures, developed and built a portable flax decortication device, built two single room (6X6 metre) dwellings and a two bedroom 90m2 house on Māori land. The second UKU dwelling is due to be completed in 2010 in Ahipara, Te Tai Tokerau (the Far North).

The research has been conducted in partnership with Māori individuals representing various hapu (sub-tribes) around the North Island. Their input has been used to identify the obstacles to housing faced by rural Māori, the available local resources, and the desirable aspects of a suitable housing solution.

Social acceptance has been assessed with a positive response from the groups involved in the research to the experience of living in earth houses. The two single room dwellings built for this purpose were initially designated as a mower shed and a laundry/storage room. They were subsequently used as a music / arts room and a wharepuni (sleeping area) for the kaumatua (elders) respectively. Both groups have indicated a desire to build more structures using the UKU method.

The University of Auckland is conducting on-going research into the thermal and seismic performance of the UKU wall panels and houses as a whole. The test results are used to determine the strength and other characteristics of the earth material so that UKU structures can be designed, consented and built.

The UKU research team works with the rural Maori communities to empower and train up locals to build using the UKU method. Local materials are sourced and processed locally as far as is practical. One of the key measures of success for the UKU research is the practical benefit of the research to the target end-users; rural Māori communities. As a result working with rural Māori communities is prioritised, supporting them through the design and consenting processes, and involving these communities as active participants building houses on Māori land.

Next we will catch up with the engineer/ builder on this project, John Cheah  to get details on this ongoing project.


Sunday, September 26, 2010

Rammed earth t-shirts that celebrate Australia

Or is it Australian t-shirts that celebrate rammed earth (and water conservation)?

No matter. It's a cute idea. Order them here.

Friday, September 24, 2010

Rammed Earth Ampitheatre at the UBC Botanical Garden

The UBC Botanical Garden opened their lovely rammed earth ampitheatre to the public this spring so it was high time I went to check it out.

The project was planned by Forma Design of North Vancouver and inspired by the Fibonacci numbers.  I didn't really see the resemblance, but it was a very pleasing space nonetheless.

Doesn't it look like Captain Kirk and Spock should be engaging in a little kal-if-fee down there?

The rammed earth walls were a joint construction project between Aquarius Contracting and Clifton Schooley & Associates

I wonder how long it will take for the free lime to leave this wall?

There are more photos of the rammed earth construction process here.

Very subtle colour variation.

I love how it looks when the soil is placed in the form in a wavy pattern.

This rougher texture was the result of experimenting with a sand-blaster.

Isn't it amazing how the finest impressions show up?

I dig these stairs!

Tuesday, September 21, 2010

Historic Rammed Earth In Ontario

Reader Alex sent some photos of his 142 year old rammed earth house in Greensville, Ontario.


The walls are 12 inches thick standing on an 18" rubble footing. The ceilings are 11 feet high inside. The interior walls are lath and plaster, with the lath being set out about 3 inches from the earth walls on wooden vertical members. 

The interior of the wall has the same earth/gravel surface with no large stones visible. On the exterior, there is a coating of  stucco or lime plaster.

He writes to say, " I don’t know the nationality of the builder, but my research led me to an owner that immigrated from England when he was young. The story that’s been passed down to the prior owners and neighbours is that the house was once a church rectory. This seems to jive with what I’ve found so far. The 1877 land registry map is labelled with the last name “Hore,” which would be Francis William Hore, who owned a mill across the street, among others, and also built a stone mansion on a large lot next to us (now the residence of a billionaire). In the record of his death, it describes that he was a churchwarden at Christ Church Anglican, which is about a 5 minute walk away, so it’s entirely possible that he built the house as a rectory for the church. As for the actual builder, I found a paper that includes 1871 census information for stonemasons and stone cutters. Lincoln District is the closest that has census info, and the breakdown is England: 21, Ontario: 10, Ireland: 9, Germany: 5, USA: 4, Scotland: 2; Others: 2."

Tuesday, September 07, 2010

Rammed Earth Home Construction in Chad

This post, the third in the series by Mark David Heath, will offer an update on the previous two projects as well as where we seem to be headed with rammed earth in Chad.

Our first project of rammed earth in Chad was the wall around our work base in the village of Mainani, near Kome, the base of ExxonMobil in Southern Chad. We built this first wall, 676 meters long (2217 feet) by 1.5 meters tall (4ʼ-11”). This site was originally used as our work base for the road work we were doing for ExxonMobil. However, with that work concluded and our work now being the composting of ExxonMobil waste material, we needed to raise the wall height. The first wall was built of laterite soil, taken straight out of the borrow pit, and screened to remove pieces larger than about 36 mm (1.5”), mixed with 5% Portland cement.

With the added height to the wall (we added about 800 mm (2ʼ-7”)) we used laterite soils again, but this time, we used “recovered” laterite soils from the roadway windrows. Through the normal course of maintaining an earthen road, soil is normally cut off the road and pushed off to the sides, creating the “windrow” typically seen all along the sides of earthen roads. If these windrows get too large in areas of high rains (like Chad) they can become a drainage problem. In a particular section of road we were building, these windrows needed to be removed to relieve a drainage issue. Since this material is typically being graded off the top of the road, it has had a lot of traffic wear and tear on it. It has been crushed and ground down by the traffic, resulting in a much higher percentage of “fines”, material that is much less coarse than the laterite material coming right out of the borrow pits.

This laterite material with higher fines in it provided results more like what we had experienced with the clay soils and sand. The higher percentage of finer material produced a much smoother and more tightly consolidated surface that laterite straight out of the pit. We still added 5% Portland cement to the majority of the extended height sections. We set our wooden forms right on top of the existing rammed earth wall, now over 4 years old and facing the fourth rainy season.

We also did an experiment with “non-stabilized” rammed earth. All of our previous projects had used some percentage of Portland cement as a “stabilizer” to make the finished product more weather resistant. The biggest issue for long-term use of rammed earth is weathering, especially due to water, in any form - rain, snow, ice, etc. With Chad having no frost, this is to our advantage. However, with all of Chad having over 30” of rain per year, rain damage is a huge issue for rammed earth in Chad.

However, I had read of structures being built of “non-stabilized” rammed earth, meaning without Portland cement, lime, asphalt emulsion, etc, as a stabilizer. I have also seen rammed earth structures several hundred years old, built with non-stabilized rammed earth. Given the possibility, and given that the expense of the Portland cement is our largest single expense in the rammed earthh, we decided to give non-stabilized rammed earth a test.

The issue in non-stabilized rammed earth is “getting the mix right”, meaning getting the right combination of sand and clay to produce a “stable” and durable structure. Fortunately, I was shown an old and simple test for determining the “right mix” which we have used very successfully. We took the principle of the test and then adapted it to our circumstances, here in Chad. Since we already have forms built for making corners of 500 mm square, and since all of our materials are mixed by hand we made up seven test blocks, using our 500 mm x 500 mm forms. We mixed up 30 shovels of material, in varying quantities, and then rammed a block with each different mix. We chose 30 shovels of material per block because it is relatively simple math to make the percentage calcs with, and a “Chadian” wheelbarrow will hold just about 30 shovels of material. Our blocks were as follows:

Clay soilsSand%Clay Soil%Sand
18 12 60.0% 40.0%
21 9 70.0% 30.0%
24 6 80.0% 20.0%
Across seven test blocks, we are able to look at clay:sand ratios varying from 20%:80% to 80%:20%, with each block having 10% more of one material and 10% less of the other material than the last block. Our objective is to see which mix is the most durable. We let them dry for at least 3 days and then, if there is no rain, we “make it rain” by watering the blocks with a garden watering can, the same one we use to add water to the rammed earth as we are mixing it for ramming. We dump about 20 Liters (5 gallons) at a time on each block, and do it 2 or three times a day.

After about a week to 10 days of “rain” we look at which test block held up the best. In Mainani, with our “recovered” laterite and sand mix, test block #5 held up the best - made up of 18 shovels of laterite and 12 shovels of sand. Since this was all new to us we were a bit cautious. We built the bulk of the wall with “recovered” laterite and 5% Portland cement, like the mix we had used to build the original rammed earth wall, 4 years ago. But, at the back of the property, where no one from the street could see (just in case it was a disaster) we built a part of the new wall with non-stabilized rammed earth, using the mixture of test block #5. We found out, very quickly, that non-stabilized is much more moisture sensitive in the early days, as it is drying, than is stabilized rammed earth. A couple of times we had rains hit us just as we were finishing or that same night,  and we found our non-stabilized rammed earth wall, living up to the name “non-stabilized”, lying on the ground when we came back in the morning. With that lesson earned, we bought some plastic sheeting and covered the fresh walls for at least three days.

Right after completing the non-stabilized rammed earth sections we had some very strong rains, including one that lasted almost 18 hours, and a couple that, while not a long, were even more intense. We were more than pleasantly surprised to see that after 2 weeks of heavy rains, preceded by at least 3 days of good drying of the non-stabilized rammed earth, that there is virtually zero difference in the non-stabilized rammed earth vs the stabilized rammed earth.

This knowledge, combined with the knowledge gained from our second project (described next) is providing what we think is the direction to now be headed with rammed earth in Chad.

In Doba we did a joint venture project of rammed earth on a residential lot. The owner put up the lot and we did the rammed earth. We have recently sold this project, recovering our investment, the land owner recovering hers, and we both made a small profit.

This project was on a residential lot measuring 25 m by 40 m and is a ʻcorner lotʼ, having streets on two sides. We decided with the owner to put two gates on the long side street. Each gate opening is 3 m wide. Unlike the Mainani site, we are trying to do a demonstration of a more typical rammed earth project. So, we have a footing under the rammed earth. We chose a gravel-filled ditch for our foundation, similar to the idea of a railroad foundation. Gravel costs less than concrete, does not need Portland cement, and distributes the loads well and allows water to pass freely, which is a concern here where we get more than 1 000 mm (39”) of rain per year. So our foundation is a gravel-filled trench 500 mm wide, which is twice as wide as the wall, and 300 mm deep, which gets us past the topsoil and into the subsoils.

We began with the installation of the corner posts which were made with 5% Portland cement. Then we installed the remainder of the intermediate posts, again with a 5% Portland cement mix. After all the posts were built, we built the wall sections, between the existing posts. For the Wall sections, we used a mix of 2% Portland Cement.

As you can see in the photos, all of the posts are “keyed” so that the Wall sections tie into them with the keyway. The intermediate posts are “Tʼs” and we built an intermediatepost at least every three wall sections. The wall sections are about 3 m (10ʼ) long by 2.4 m (8ʼ) tall. This project was covered in greater detail in the previous article.

After having built the walls and we build two small buildings inside the walls. One was a one-room structure that could serve as a guard house, situated between the two gate openings. The second structure was a 60 m2 structure with a bedroom, a bathroom and a “great room”, a living room / kitchen combination room. The photos show the windows formed out and then having a beam poured over them as we poured the bond beam.

This project received a lot of interest and a lot of folks coming to look at it. They spoke well of it, of how thick the walls were, etc., but we had no one willing to buy it. Our partner was thinking that she was going to have to live in it to prove to the Chadians that it was a good product. Then, one day, we were talking about the project and she said that she has overheard someone talking about how they did not trust the project because the rain had eroded the walls. We had built this right at the beginning of the rainy season and we intentionally did not cover the walls to see just how much damage the rain would do to fresh walls. What was a good thing to us, showing what we felt was very little degradation, seemed to have become a really big negative to anyone who came to see the project. The owner suggested that we plaster the walls. This would cover up the rain erosion and it would make the walls look more “familiar” to the Chadians.

Traditional brick walls need to be plastered or the rains will wash away both the bricks and the mortar as can be seen. So, even though we understood that the minor erosion that had happened to the Rammed Earth wall while it was still fresh and before it had hardened was all that was going to happen, the Chadian thought that it would continue and eventually eat out the entire wall, as happens with traditional bricks.

So we plastered the two walls facing the street, being the two walls facing the prevailing wind, which were the two that had taken the most abuse and suffered the most erosion. We plastered them with a “tossed” or “thrown” plaster made of sand and Portland cement.

The result was that the walls looked just like any other plastered wall, except for being twice as thick, and, that they were immediately accepted by the Chadians. By the time we had the first two faces plastered we had 4 offers to buy the project, and before we started on the third side, we had it sold, and cash in hand. Another demonstration that, especially with new products, you need to be sensitive to the customer and find a way to get them to accept the new product.

With the outcome of these two projects, the one with successful non-stabilized rammed earth seems to be offering us a more clear direction in which to proceed with rammed earth in Chad. Since the Chadians prefer the stucco look, and since non-stabilized rammed earth can be built to deliver similar performance to stabilized rammed earth, then it seems to us that the way to go is to build  non-stabilized rammed earth, then plaster the walls. This save the expense of mixing Portland cement in the rammed earth, delivers the same performance, as long as the rammed earth mix is correct, and the saved Portland cement can be used to plaster the walls, making them acceptable in the marketplace and even more resistant to the rains.

This new direction could really help in the general acceptance and diffusion of rammed earth technology in Chad. Rammed earth is faster than either CMU (cement block) construction or traditional brick construction. Rammed earth is much thicker than traditional brick and stronger than CMU or brick. This offers greater security to the occupants. Being thicker, the heat of the sun will not get through the walls, making the structures built with rammed earth more comfortable. Now, the knowledge that  non-stabilized rammed earth can be built with comparable performance to stabilized rammed earth, means that rammed earth is now economically competitive as well. It was already less expensive than CMU construction but more expensive than traditional brick. Now we are even less expensive than traditional brick construction, as well.

The single biggest roadblock seems to be the initial cost of the forms. Although this is not a huge issue for an existing construction company that is going to be going into the rammed earth business, it could be for a small enterprise. We are looking at trying out a forming system that will make large “blocks” of Rammed Earth, about 1 000 mm long, 250 mm thick and 500 mm tall. These would have to be built in a “bond” pattern, similar to laying CMU block or brick, but this technique is already well understood. The initial cost for these smaller forms would be significantly less, and, with two sets, the speed should not be too compromised. We still need to sort out how to build corners, and intermediate posts.

The owner of the Doba project is now so pleased that she has formed a small construction firm, hired a crew, and is building a project for a new client and has already signed two more clients. We also have a young, newly graduated engineer, whose father has a long-established construction company, doing an “apprenticeship” on these first new projects. So, we have what looks like the first two adoptees of the rammed earth technology in Chad and we have the third project underway, and two more right behind them. The first project, in Mainani, is being actively used as a yard for making compost from Esso waste, the second project, in Doba, has been sold and is nearly completed and ready to be occupied by the new owner. The third project is underway and going well with a new adoptee and a new apprentice. Rammed earth in Chad may be off to a new role in the battle against desertification.

When we first built the walls in the second project we thought that we needed to have at least 2.5 to 3% Portland Cement in our mix. We know now that we were basing this on short-term issues. With higher cement content it is true that the walls eroded less in the rain. However, with the correct mix, we now know that the walls get very, very hard with time and if we protect them from early rains, we can build excellent structures with 2% Portland cement and without any Portland cement, at all.

What our experience has now shown us is that rammed earth takes a significant amount of time to fully harden. However, with that time, it gets really, really hard. When we went back to cut in the windows on the walls where we did not form them in, we found that our rammed earth walls were every bit as hard and as difficult to break open as the concrete construction in the area. The crew assigned to cut out the window openings kept going on about how surprisingly hard the walls were. There were a couple of doubting Thomases that were converted watching the windows being cut into the rammed earth walls that had now hardened for one year.