Building progress

The building will be a seed bank and small workshop. It will serve as support the work in the garden and will in future have an attached greenhouse. This program allows the work to be done quickly (during the workshop) because it has little need for finishing and infrastructure. But their shape and size can be used for other programs, for a small bungalow or even if multiplied, for a small housing unit.

The vault shape was chosen for its simplicity. This is a shell structure in which a single element creates the space. It’s a wall that becomes a ceiling and turns back into a wall. There’s a single material and for the entire building. It renders useless all parts, and their associated costs, envolved on roof building, such as beams, trusses, etc. and their connection with the walls. Costs, time and resources needed for this construction can thus be reduced. Plus the space created is comfortable and cozy.
The vault’s section will be a catenary. This is the shape created by a chain when suspended by both ends. When mirrored, this form can be used to create the most efficient arches and vaults as all forces are transmited down the entire structure as compression forces (under which adobes work best).

Regarding the materials used we also decided to go with simplicity. The foundation will be built out of cyclopean concrete – a concrete with most of its volume (in this case more than 60%) composed of large stones. This allows us to get great stability, prevent capillary effect on the earth walls and to lower the use of cement with the addition of a material found on site. In the future we intend to research on alternatives to this type of foundation so that we can totally avoid the use of cement. The structural layer will be built out of adobes because it’s a very suitable technique for this solution and because and we want to learn more about it. For the outer layer we started by designing a green roof, but as an experiment and aiming to minimize the use of plastic membranes, we decided to try a lime plaster. It will be an opportunity to explore the application of linseed oil to improve the impermeability of this type of finishing.

The technical drawings are available here. They will (for sure) be updated and changed as we progress in the workplace. New versions will be available.

There are several ways to build a vault. We chose to build this one using some formwork to lay down the adobe bricks. In the future we want to try the method developed in ancient Egypt (Nubian vaults) that avoids the use of a form but that is technically a bit more demanding.

To create the catenary shape we could have used a computer generated graphic to collect the necessary coordinates and draw this curve. However we decided to use a more appropriate sollution. So we hung a chain with the size we needed and built the first part of the formwork by screwing wood boards directly on the wall.

The mold is used following four successive steps: 1st the mold is placed in the desired position and elevation; 2nd the adobes are laid over the mold to form a section of the vault, 3rd mold is lowered separating from the adobes; 4th the mold is moved to allow the construction of a new section of the vault. We’ll continuously repeat these 4 steps.

We’ll finish the lifting system really soon!

The foundation work is almost ready. It took three days of intense work and two of us for this phase. We use cyclopean concrete (with large stones) with a mixture of 1:4:3 (cement, sand and gravel, respectively). The stones were gathered in the meadows of the farm getting them cleaner and more accessible to the harvester.

Concrete was poured in two pits – open with a backhoe – without the use of formwork (directly against the land). We’d first lay down the stones, trying to get big gaps between them and then we poured a sufficiently liquid mix so it could sink in. We used almost 40 litters of water to 20 of cement, 80 of sand and 60 of gravel.

We’ll be working on finishing the foundation very soon.

We’ve just finished the formwork’s lifting system. 4 adjustable footholds will allow to perfectly level the whole formwork so we can lay the adobes at the required hight.(see SEED BANK POST 2 – FORMWORK).

The system is a little slow but it allows a great versatility and accuracy.
The template is already in the works!

Recently we went to the Department of Civil Engineering at the University of Aveiro to test various adobes, made from different soil mixes, under compressive strength. The opportunity was given to us by Professor Humberto Varum and we were helped with the tests by the Engineer António Figueiredo. We’d like to thank the two.

Our goal wasn’t a rigorous scientific test but rather a simple test so we could determine witch mix can produce the adobes with the best behavior under compressive strength.

To make the adobes we had four materials: clay collected free of charge from about 8 km away from the building site; sandy soil – with little clay – collected on site; bought sand and horse manure that we also had to buy. We did six different mixes and in half of each of them introduced the horse manure. Thus we tested 12 groups of 2 adobes each (for a more rigorous test they should have been at least 3) 6 with manure and 6 without so we could also carry out a comparative test by analyzing this variable alone. The following image illustrates the various proportions and results in MPa (mega pascal). The graph shows the results of both adobes tested for each mix.

The adobes with greater resistance (excluding those with a greater concentration of manure) were made from a 50-50 mixture of clay and sandy soil plus the horse manure. This means they are optimal from both a structural stand point and an economical one because we can make them from free material. This will be the mix we’ll use.
Regarding the manure the results confirm our choice to use it. Specially in clayey soil 20% of manure increases the compressive strength by about a third (the effect is less prevalent in sandier mixtures). In the mixture with 33% of manure the results are really encouraging as it made the adobes much more resistant. Besides the adobes are left with a lower density (lighter) which is also better in structural terms. In the future we want to take deeper look into this factor, finding the limits and the optimum value.

We finally decided what would be the detail of the contact between the wall of the vault and the foundation. The main concern is to protect the adobes from the water not only in direct contact but also, and perhaps more importantly, in contact through capillarty. Capillarity or capillary action is the physical property that liquids have to travel, even against the force of gravity, through very narrow spaces. This happens even in the microscopic spaces between the particles that make up the solid materials such as stones, concrete and many others. A simple image to understand this phenomenon is that of a sponge that, when sitting on a surface with water, becomes progressively wet. The water is “sucked” up into the sponge. The same thing happens in the foundations and walls of buildings with water found in the soil. In the case of building with earth this is definitely a phenomenon to be taken into account.

As a first protection we designed a drainage ditch around the outside perimeter of the building that will be filled with a perforated pipe and gravel. All this is wrapped in a geotextile membrane that will filter the finest particles preventing the system from clogging. Then, upon the lintel of the foundation, we build a layer of cement blocks filled with the concrete remains from the foundation. This will allows that the adobes are above ground level and avoid direct contact with water that, by accident, is able to surpass the drainage ditch. In order to cut the capillary action we applied a layer of asphalt emulsion and what we call a cement “Flashings” that separates not only the adobes from the foundation but also the lime plaster that we’ll use as waterproofing.

This part was made using a technique we learned in TIBA called “plastocement” – cement reinforced with a plastic mesh, potato bag style (you can actually use potato bags).
It is a very versatile technique that uses cement in a “responsible” way. The parts produced like this, which will be only 1,5cm thick, can be used for multiple purposes – water tanks, dry toilets, stair steps and even boats.
Five simple steps to create these DIY prefabricated parts:
1 – Use small boards – only 6mm thick – to make a form for the piece and fill (the 6mm) with the cement mix of 1:2 (cement and sand, respectively).
2 – Cover with mesh (recycling potato bags) previously cut to size and soaked in “cement cream” (cement mixed with water until it reaches the consistency of cream). This cream binds the layers together and renders the part waterproof.
3 – Create a new layer of form and fill it again with the same cement mix.
4 – Create the mold for the small tab on the bottom part and fill it.
5 – Wait only 5 to 10 min and remove all the form pieces carefully. Let it dry about 2 days watering regularly after the first 12 hours.
Ready! (More information about this technique in the future)

Since we began producing adobes systematically (3 years ago) we managed to optimize the process. At first, without any mechanization, a three-person team – starting with a pile of earth (not sieved) on the site – would produce about 200 adobes in 8 hours.
At this point, after optimizing the production process, from the same pile of earth, three people can produce about 900 adobes in the same 8 hours.

(homemade) Sieve and mixer grouped together.

This is our current rate. We’ve achieved this improvement due to optimization of routes but mainly by the mechanization of the sieving and mixing stage.
For this building we’ll need 1500 adobes.
This is the outline of the production space.

The main problem in the production of adobes is the logistics related with drying them. The adobes can take from 3 days to 3 weeks (depending on season and climate) until they can be stacked. In a continuous production the accumulation of adobes in the drying stage would be enormous. So the production days were intercalated.

For now we only work with a single adobe mold although we plan to test other solutions. In smaller productions we normally unmold the adobes on boards (usually 2.5 m long) laying on tables. This allows a more comfortable working position and to stack the boards saving space during the drying stage (check out this video from an adobe production we organized the TIBA – Brazil).
In this 900 per day production the usege of boards would be gigantic (900/15 = 60 boards per day) so we decided to work directly on the ground, like it is done for ages. Although the working position is not as comfortable this method has three major advantages: less material costs, faster by avoiding several steps in the production (transport boards); no losses in the drying process – on the tables, by promoting an uneven drying the upper and lower face, around 5% of the adobes crack.

Now that everything is ready to start building the vault lets just do a little math to have an idea of the forces in play.

Imagine a section of the building only 1 meter long.
The data is:
Area of the Vertical Section = 1,26m2
Therefore
Total Volume = 1,26 x 1 = 1,26m3
Knowing that the…
Material density = 1730Kg/m3
Then…
Total Weight = 1,26 x 1730 = 2178,8Kg
This means that the…
Wieght per “Foot” = 2178,8 : 2 = 1089,4Kg

Now looking to the data on the adobes we got while testing them under compression (more here)
The data is:
Tested Surface Area = 33600mm2 = 336cm2
From the press we got…
Force at Rupture = 47900N = 4884,44KgF
Deviding the value by the total adobe area we know how many kilos can be applied per square centimeter.
4884,44 : 336 = 14,54Kg/cm2

This is the value at the rupture point. For this exercise we’ll only use a fraction of this result. Because we don’t want collapsing buildings an because in the handmade production an laying of the adobes there will always be some anomalies and variations, we’ll use only a third of this value – 5Kg/cm2.

Let’s take a look at the “feet” of the vault.
The data is:
Foot Area = 18 x 100 = 1800cm2
Therefore the…
Weight per foot = 1800 x 5(Kg/cm2) = 9000Kg
This means that the whole weight of the building’s section can be…
Total Weight = 9000 x 2 = 18000Kg
From this number we calculated the possible height of the vault…

In a vault with these dimentions other forces (like the wind and what not) come into play but this is just an abstract exploration to know the material strength.
Even so, we started the building’s first section filled with confidence…

The foundation was ready, the adobes were dry and the math was done… there was only one question to solve… which should be the orientation of the adobe joints, should they be vertical (1) or horizontal (2). The answer was not easy to find by researching. In the end the answer came from Architect Gernot Minke to whom we wrote with our doubt.

The answer: From a structural point of view the differences are negligible. So the selection criteria became only those related to the building process. And having vertical joints (1) is much better because you don’t need to fit in the adobes from a new section with those on a previous one.
Everything was ready to go.

From this first experiment we wanted to solve three main doubts:
1- Would the vault hold…
2- What would be deformation of the vault when lowering the formwork with a short drying time (we actually took it out only 20min after we finished the adobe laying; we needed short drying time to be able to build everything in the 7 days workshop coming up)…
3- How long and how many people would we need to build a section of the building…

And we got our answers:
1- There was no problem; everything went according to plan with no cracks or anomalies.
2- We actually tried to prevent this deformation by adding more sand (coarse) to the mix. Increasing coarseness gives more stability to the mix during the drying process. 24 hours after lowering the formwork we could measure a deformation in the center of the section of about 2cm downward and 3cm forward (in the direction of the last adobes to be laid). Because one of the ends of the section has a slightly shorter drying time, being laid with a small default, deformation is higher creating a “Pisa tower effect” (I just came up with it). This deformation wasn’t that important and we’ll be able to correct it in the next section.

The adobes are laid creating a diagonal to facilitate the laid of each row. Thus the small asymmetry in the drying times.

3- Four guys, organized in two teams (one laying and the other “serving the adobes)could build a section of about 70cm (6 columns) in about 4 hours. But we could clearly spot an increase in speed as we got more experienced. I’m sure that experienced workers (and maybe a 5th guy helping around) could easily lay two metters (about 500adobes, 28 columns) in an 8 hours working day.
Latter we’ll publish the specific complexities of this task.

While we don’t publish the rest of the building progress you can check the photo album on the Building with Earth Workshop we organized in Augost 2011 HERE.