A quick update on the progress of the cob shelter

Before writing more in detail about the techniques, I want to give a brief update with a couple of pictures to show, how the project has progressed over the last two month.


Now it was time to cover the whole place with a tarp. There was quite some rain during August, so I needed to create a dry spot, where I could mix my cob and at the same time to protect the structure from rain.


I still covered the walls with to protect them from drying completely. This way, it is easier to build on and to work wet on wet.


By now, however, I leave the walls uncovered under the roof tarp. They still contain a lot of water. And soon I want to put on the final roof construction. This will require that the structure is sufficiently dry and strong.




The straw balls turned out to be very useful as steps to reach the top of the walls. And they are very easy to move from spot to spot. Straw balls are sufficiently strongly packed and give a good stand, even on less plane underground. And they can also slightly lean against the wall, so you can stuck several of them on top of each other and still stand on them to work on the very top of the structure.


Alternatively I use some milk cases to reach the top of the wall. Then I use a wooden board as a firm base to stuck them onto each other like steps.


Soon I can connect all the different parts of the wall above the window and door line. And then, the roof will be installed.


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about breads, croissants, macaroons and pieces of cake

In this and following posts I go more into depth with some of the different steps in my  cob building project. The first will be the actual making of the cob mixture.

But let me start by making two general remarks

i) There is always plenty of ways to achieve a certain goal. Building with cob is extremely forgiving. Virtually every “mistake” can be saved. So in particular cobbing can be done in very different ways. In the end the final structure is the reward. And of course all the fun you had on the way building it. Here I just want to describe what has worked for me. So far.

ii) Working with cob is ideal for working as a team and in a group of people. Cob allows for so many different designs. Obviously, inspiring each other and combining different ideas into the same building can be a very creative process.  More than that, there are also a few very practical advantages of working in a group. For example, the actual mixing of the cob is usually done in groups of 2 people.

I have been working all by myself so far. And to do so, this required to reconsider some steps, which I want to detail here. So this maybe for you, who is standing alone with the task to mix a portion of cob. Or it is for you, who is ready to take the challenge – against all odds – and make a cob building all by yourself. 8)


As I mentioned in an earlier post, my garden ground is fine sand, no clay. To work in cob I had to get some clay from outside. Luckily, a garden neighbor with fine clay under the top soil duck out a hole for a septic tank, and I received about 3 cubic meters. Some initial testing gave me the impression that it contains more than 50% clay. The rest is silt and sand and top soil. But also a few flint stones that have the tendency to break into sharp pieces, when I dig with my spate in the pile. But even broken bottle fragments or rusty iron tubings can be found in my pile of clay. “Nocking on wood” I have been able to spot them all before any major injury.

The best practice of course  would be to dissolve the clay in water – liquid enough – to strain the clay through a suitable mesh thereby filtering stones and other unwanted additions like roots and potentially dangerous incorporations like glass fragments. But it does not require much water to achieve the wanted consistency of the final cob. And straining the clay would easily make it too liquid for further processing.

About 6 to 8 l of water is usually enough. But it depends very much on the weather. The clay pile is covered with a tarp. So for the clay rain does not make a big difference. But sand and soil are open to rain. And therefore it matters a lot, if it has just been raining, or if there was a period of drought before making the mix. I always try to start with as little water as possible. Although it is tempting to add more water than needed, as mixing becomes much easier with more water. Obviously.



All the extra water I first add to the clay in a separate big bucket. Preferably already well before use. This way, the clay becomes sucked in water and is easier to mix with sand and soil.

I mix one (overfilled) 10 l bucket of top soil with 2 buckets of fine sand and two buckets of the clay rich fraction. Assuming that the clay rich fraction consists of at least 50% clay, my final mix contains at least 20% clay.

Now I mix the different components by stamping them with bar feet. Toes and heel become very different tools. And they are very efficient tools for mixing and forming the clay mixture.

In the beginning I often pull over the tarp to bring back sand and clay to the center of the tarp. It is this very early phase of mixing, where it is easier to be two people. Each taking two corners of the tarp to swing and role the mixture from left to right over the ground. But also with my method, eventually, the mixture has improved to an overall stickiness, that I can form a need little croissant (more precisely a chocolate croissant) by slowly pulling over two corners of the tarp at a time from all 4 sides.


This croissant has the tendency to unroll, so to stabilize the cob in the center of the tarp I give it a few careful kicks, giving it a cone-like shape. Maybe better compared to a giant macaroon.


Now I stamp the whole mixture through again starting at the edges of the macaroon,


to then work my way through its center. The idea is to keep the mixture as much as possible contained in the center of the tarp and to mix thoroughly rather than spreading it out so quickly. …because forming a 60 l soil croissant is hard work.


This process I repeat up to 10 times. 10 croissants!

Looking at this last picture you may think that it is now properly mixed and ready to add straw. But I actually gave it another turn. One more croissant. My experience is that thorough mixing is very crucial and makes every subsequent step, like adding the straw, forming the bread shaped portions, or building them onto the wall much easier. So if I have any doubt, that the mix is complete, I rather give it another turn!! And everything else becomes a piece of cake and real joy.

First then I add straw to the mix. To do so I collect everything once again in the middle of the tarp, form the cone shaped mount and form it to a thick disc.


Then I add a first portion of straw evenly on top.


And stamp the straw into the clay mixture.


… add another portion,


and stamp again. You can now see that there is less straw in the center of the mass, because here is most of the clay mixture.


Therefore my final addition is mostly in the center of the mixture.


Now I stamp it in as good as possible.


Then I collect everything including the straw once more as before


This final time of stamping I really take care to keep the straw embedded in the clay mix. To do so I try to span the edge with my toes to avoid the straw to brake out and to preserve a closed surface. That makes it easier later to form the portions.


Now it is flattened out evenly like a pancake. You can hardly see any straw, but in fact, there is about as much straw in the clay mix as you can see in the mount of loose straw behind, placed there for comparison.


Then with a plucky pull on two corners of the tarp, the whole pancake loosens from the tarp. And its is easy take some portions to form them into breads.


Finally a few numbers…

To mix 60 l clay sand and soil and finally adding the straw takes me rawly 2 h.

Another half an hour to 1h it takes to form the 50 – 60 breads.

Cobbing the breads onto the wall can take everything from 30 min to 2 hours, depending on the particular task on the structure.

Taking together, working two such portions a day can be 10 h of work.

Usually I make 4 portions over 3 days. And have plenty of fun with the progress.

You can always call it a day. Best before adding the straw, or after forming the breads. In both cases, the final product can easily be covered or wrapped in a tarp and kept over night.


In fact, after overnight the consistency of the mix usually becomes even better for cobbing. It is probably even better sucked through.

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Integrating a channel for fresh air intake in the cob wall

I expect the shelter to become very air-tight. Or at least the ambition is to get it as tight as possible for good temperature control. The only really critical part, where cold air might blow in uncontrolled is the door. But if I buy a ready manufactured door, it should become really tight.

However, it would be desirable to have the possibility to open for some controlled fresh air intake, in particular when the rocket stove is running.

Therefore, I have now integrated an air-intake channel in the cob wall. The channel should give me the possibility to open for some controlled air flow into the shelter. The direction of flow should simply be driven by the draft of the rocket stove.

I got 3 minor pieces of a flexible plastic pipe in a useful diameter from a dump container. I just had to piece them together using a few cable ties.

I have placed the channel with the intake to the west facade to take the air directly under the roof overhang. The tube then runs along the wall, but strictly downwards to release the air about 15 cm above the floor at the northern wall inside. If condensation water would develop, it would run downwards into the shelter and could here be collected in a little container. However, in winter time, the air in the tube would most likely warm up on the way through the intake channel in the cob wall. And therefore I do not really expect much condensation to occur.

At first I hesitated a bit to place the pipe along the wall. I was afraid this may compromise the walls stability. But after having ‘cobbed‘ the pipe in, I feel that the pipe may even improve the strength, because of the direction of the reinforcement by the straw, which – I imagine – after pushing the straw with the rod, will be placed needly and snuggly in the corrugated outer structure of the pipe.


After day 1.

And after day 2.


Last not least, the status quo



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cob shelter, plan and update

I had to apply for permission to raise the shelter in my garden. Because the garden colony area is under nature protection, the regulations are rather strict.


I got a friend who is good at google sketchup to draw a quick sketch.


The south front is all in glass and is directly extended with a greenhouse of 5 m2. The cob construction is thus limited to three walls, west, north and east. The dimensions of the sketch are not quite right, but it still illustrates the idea.

The roof construction will be from wooden logs, used floorboards and topped with a layer of soil.

Last winter and in preparation for the construction I fell a few Nordmann firs in a nearby, old-grown christmas-tree plantation. Of course with permission of the owner.


That was quite challenging as there is hardly any spot in the densely grown forest to let the trees down. And I promised the owner of the forest to not create any clearings, but rather to pick a single tree and then move further to another area. So all trees had to be taken out from another densely grown area. Consequently, the only way to get them down was to clime the trees with a saw and cut all branches and the top before falling the remaining trunk with the power saw. This is probably not the way to pay one s last respect to a tree. But at least I tried to do it quickly.

The axe was used to strip the bark, which was best and easiest done within a few weeks after falling. Preferably immediately.

I left the trunks in the forest, where they are still laying – off the ground – in the dark forest and protected from direct sunlight not to develop cracks.

I just brought a single one home to the garden, because I had to find out if I could do it with the sack barrow as I envisioned.


And yes it worked. By now they are much dryer and lighter.

The west wall is taking shape. With a critical look at the cob work you can still see the different layers of different working periods. When I work day by day, I can on the second – and even the third – day still work the cob from the first day by pushing the rod from the side to punch holes. When I take breaks, the cob dries so much, that it is impossible to form it any longer.

You can see from the form of the wall and the color nuance the result of 4 times 3 days of work. The tiny part of the wall to the very left is by now completely dry and as hard as concrete.


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Improving the techniques (cob)

One of the big advantages with building in cob as compared to other methods is the extreme flexibility. It is almost impossible to mess up. There is always a possibility to correct afterwards. For example, when the wall becomes to thick at some point, you can simply saw the excess down again. You do not even loose your material, because you can soften it with some water or simply add it to the next portion you mix.

However, there is a good reason to develop some routine and to work in a more organized fashion not to do futile work. It is nice that you do not loose you cob material when you take parts down again. But anyway, pounding the mix, forming the balls and working them onto the wall is hard work. You do not want to do this over and over again.

I have developed some routine by now. The first routine concerns mixing and forming the portions. All in order to build a straight wall from the start.

In the beginning I formed the portions as balls. But it turned out to be a lot of extra work for the hands. And it is not easy to get even portions. They turned out to be very different in size. Now I form them as flat discs, also called breads.

It reminds a bit of a bakery, does’nt it? Biscuits left and breads to the right.


And here is how I make them.


Once the mixture is homogenous and the proper amount of straw is added, I collect everything one final time in the center of the tarp.


And now I pound it one final time and as evenly as possible like a flat pancake.


Then I loosen it by pulling the tarp over one time and only in one direction. Now it becomes very easy to pick portions of equal size. I just need to close to edges of the portions to form some bread-like shapes.


Ready. Now its time for a break.


Home made rye bread with ramson pesto.

The other part of the process that deserves some degree of organization is the work on the wall itself. Instead of pushing the rod higgledy piggledy from all sides into the newly places bread, it is advisable to first tag it by firmly and deeply pushing the rod in all directions through the layer of cob underneath.

So far so good. I stopped counting the days. The only thing I know is that I need a day off. 8)


And above all, I do not know how many holes I pushed in the growing wall. Must be in the 10th of thousands by now as judged by the wear out seen on my first pushing rod, which needs a replacement.


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I am building a cob shelter

I have started building a cob shelter in my garden on the country side. The structure is going to be 10 m2 and combines to the south side with a 5 m2 glasshouse. The floor level of the shelter will be about 40 cm below ground. This is just where the top soil layer turns into sand. This will give me a better foundation.


I started by laying down a row of 50 x 50 cm floor tiles as the bottom of the foundation. The tiles do though not provide a capillary insulation from below. Therefore I needed to place some big stones, natural rock, on top of the tiles in order to build my cob wall separated from the capillary forces from below.


It is a bit of a puzzle to place the stones on the flat tiles. Obviously, for a good foundation they need to get into a firm position. It is a matter of try and error.

But in the end I succeeded. Now I can walk over the stones without them moving. The rock foundation is now up to 50 cm broad, enough to build a 30 cm thick cob wall.

Finally I can start building in cob.


After a number of tests I decided to mix 2 parts of my clay rich soil fraction with 3 parts of sand. The amount of water needed to reach the proper consistency is very tricky, and has to be adjusted on the daily bases. Depending on wheather and rain fall.

After mixing by pounding the mass with bare feet on a tarp, I add straw to the mix. Not too much at a time. But the goal is to include as much straw as possible. Straw has many functions to the construction. It increases the tensile strength of the wall. But it also serves as an insulation.


Finally, I take portions of the cob to form to balls ready as building blocks.


30 cm thick, 40 cm high and about 3 m long is the result of 6 days of work. Not too bad for a start.

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Capitalism is a culture of waste

There is two ways to define waste. One is, that an item turns obsolete and cannot be used any longer. The other is that the item is toxic and therefore of concern for the environment.

Ironically, both problems are man-made.

Now it is time to address both of them.

Poor people, in particular in poor countries, generally do not trash things because they always find a use for everything. Things don’t turn worthless, just because they no longer serve the original purpurse. Everything can always be used for something. After all, it exists. Why burning or burrowing it?

Not because poor people were concerned about the waste as toxic waste. Initially not. Now, they are – for good reason-, as trash from industrial production is shipped to and disposed on their land. But in the first place, poor people lack money and therefore live a ressource-based economy, with trash being part of their resource. A very natural behavior indeed.

Recently, a new concept has been promoted that should solve our problems connected to waste: The concept of ‘cradle to cradle’. The idea behind ‘cradle to cradle’ is that all our production should be made of harmless, easily biodegradable material.

Michael Braungart, one of the early proponents of the system, is looking for a society, in which wasting makes sense. And his idea is being celebrated as the next industrial revolution.

The concept suggests that we, the consumers, will not have to make any effort. We are not required to change our habits. Instead, the industry promises to solve the problem with new products of no environmental concern. And we as consumers will be allowed to proceed with business as usual.

Such a revolution is made for the industry, which otherwise is in serious danger to run out of business. Such a revolution is not for the people or the environment.

The idea of ‘cradle to cradle’ is nothing new. ‘Cradle to cradle’ is simply nature’s principle. Coming along to suggest ‘cradle to cradle’ as a new concept for industrial products should make the products commercially viable.

Waste does not need new ideas. The very idea of waste has to vanish. Both because the products should be of no concern for the environment, but also because products have to last and fulfil endless functions in the natural cycle of matter and energy.

One of the reasons that led to the great depression in the 1920th was that the market was saturated. Production, and therefore employment and buying power ran dry, because the market was saturated with sound products of robust quality. Products were designed to last, putting the industry out of business. But putting the industry out of business also put the money out of business.

In the 1920th, people were challenged, but did not succeed to free themselves from the commercial interest, maybe because they did not trust in the power of community. Or, maybe because the industry was too quick to prepare for a plan B: The idea of making industrial products planned obsolescent.

But this time we have all the tools to get this straight. This time we gonna make the money – not the products – obsolete!

Nature is rich and does not economize. But nature doesn’t waste. Waste by definition does not make sense in nature. But Michael Braungart is “seeking for a society were waste makes sense”. Another industrial society selling us, this time harmless waste, but still for money.

We need to find ourselves in nature instead of trying to imitate and remodel our man made commercial system with products that can be wasted with good consciousness. The abundance of nature we can only experience in nature.

Cradle to cradle is nature’s principle.

Trying to imitate it, we will most likely fail.

Doing it for money is criminal.

I have a serious problem with the idea of manufacturing solar panels. Solar energy has been the principle driver of all energy and material transformation on our planet. I cannot imagine that we will be able to design a more efficient system to capture solar energy than what evolution has developed for us and including us. The vegetation is the perfect solar panel. Removing the vegetation in order to make room for dead, unlasting technical devices to produce electricity can only be in the interest of the industry and money. The vegetation does not only provide us with energy, but with products of all kind. From food to cosmetics. From building material to clothing.

The technology and the solutions for our sustainment are right in place. We only need to share the knowledge about it.

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