Dome made with unfired earth bricks

The first post explained, in general terms, how the house was being built. I will now talk more specifically about the dome that I am building over my sons’ room. My son Pablo Mateo is the one in the following picture. He was born in 2006. He likes to pass time in the building site and often helps. He is sitting there in the roof, in a thick wall (60 cm wide) that divides the entrance corridor on the right and his room on the left. The wall is thick and can easily support the weight of both domes. The thickness of the roof is a fraction of that from the wall. Therefore the roof is, in relative terms, light and can be supported by the wall. Where my son sits water accumulates so something like a water gutter was made later on (not shown in the picture) in the middle to drive the water out. After the gutter was made both domes were covered with a 3-4 cm width layer coating of waterproof cement. Before cement was used it was necessary to cover the roof with plastic to protect it from the rain, that is what you see behind my son.

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My son also likes practicing Kung Fu. The following picture is not related with building techniques, but I am so proud of it that I published it here :). He is practicing in our “garden”. That place is next to our property, next to the building site. It is where we currently rent and live while the house in being built.

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In order to make the dome you start by laying arches on each corner of the room.  A dome or a vault can be seen as the addition or superimposition of several arches, which by themselves are structurally a strong form. You add a little mud on a dry brick and place it over the previous arch by making sure that you form a new arch. You can place it slightly higher or lower in relation to the previous arch in order to control the curvature of the roof. The following pictures give an idea of how it is done.

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As shown next, you can make mud by using earth from your own ground. To gain garden space, I take it from the wall where my smallest son, Miro, is sitting. You could also take it by digging a whole on the ground. If you dig a one meter deep whole I think that chances are high that you will find quite good earth for that purpose. To make a strong “plaster” mix it well until nothing is left dry and a kind of a thick mud soup is formed. Once done and when it is quite liquid, but not too liquid, you can place it in a bucket and use it to place the bricks.

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Before placing the bricks my son Pablo Mateo some times works on them to let them more uniform. It is not always necessary, but he likes to keep busy. He is a great company and helps to have a good time in what can otherwise be a lonely job. What helps a lot too to make the job nice is to hear to music while working.

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The process is not too hard and with practice it becomes natural and can be improved relatively fast. You just need to make sure that you always keep forming arches. You place bricks as shown in the pictures that follows. The two corners will eventually merge and you keep on going until all corners come together. When each arch is closed you work on the final brick in order that it fits well in the middle and the arch is secured.

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As I explained before these are the conditions that need to be satisfied to make the dome:

  1. The bricks dimensions are more or less 20x10x5 cm. Bricks are not too small nor big, not heavy and relatively flat. The area used to “glue” them is big in relation with their width.
  2. Each time an arch is formed which lies over the previous arch. If the arched shape is lost the roof can become unstable and fall.
  3. Little mud is used to glue the bricks. They must be glued dry, like that they stick. If the bricks are wet or too much mud is used they can fall.
  4. Each corner starts with a 45 degree angle with respect to the horizontal plane. Like that every brick in the roof is under compression. If the angle is bigger the roof could have parts that are not under compression and could break.

In the following picture you can see how the different beginning points of the roof, starting from each corner, are united. I used a mask to protect myself from the dust because I had a bad cough those days. Probably caused by some allergy.

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The room is more or less a triangle therefore the other side of the room starts on only one corner, laying the first arches of the roof against the wall. That pointed part of the room has a window that connects to the living room.

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Since the room has three corners once the roof corners starting from them come together they form a triangle. If they had four corners they would have formed a square like the one you see in the other dome in one of the following pictures taken from outside. From inside the roof looks like this:

11116217_10153349285463401_2517307646515871329_o From outside, near that building stage, it looks more or less like the following picture. I closed a bit the triangle on the corners. On the right side you can already see a bit of cement over the domes. Each dome generates a force against the wall but since they are placed one against the other and the walls are thick the horizontal forces are partially eliminated and relatively weak. That leaves mostly vertical forces over the supporting walls.

In the front part of the next picture you can see the start of yet another dome. That one will cover a bigger surface over an irregularly shaped room. Therefore I left if for later and made the domes over the smaller and more regular spaces first. Like that I have time to acquire skills starting with the simpler rooms.

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From outside you can see how the domes look as well as the entrance of the house. I am over the roof placing the water proof cement layer in order to protect against the rain. The cement will be painted in order to make it look nice. I will probably use a cement based paint. The paint will be a mixture of white cement, calc, salt and iron oxide to give it the colour. It is a cheap paint, looks nice and lasts for years.

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It is not too hard to imagine how the end roof will look like. Basically each room will have its independent dome or vault or a mixture of both over it. It will be like if several differently shaped domes come together one against the other. That gives them structural strength since like that the forces tend to push the walls down and not to the sides. It is important to see what to do with the rain water. It could be redirected outside or inside and collected in order to re use it. In the picture above you can see a little bit that in between the two domes, or between the two arches, there is something equivalent to a gutter that redirects  the water outside.

The construction is paused while I am now in Sao Paulo visiting my oldest son Martin. He was born in 1993. Here we are both in his apartment, resting and being together. I hope I con convince him to drop the city life and come live with us, like that we can build something nice 😉 and explore the Chapada Diamantina !

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I am sure that he would like to explore some of the places near where I live, like the Vale do Pati in the picture below. That probably beats sitting behind a computer 😉

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Best wishes !

Jrv

5 thoughts on “Dome made with unfired earth bricks”

  1. I have not so happy with waterproof cement over the vault/domes. You get small cracks and while the roof does not leak it allows damp. Also cement is expensive. I didnt know what else to do. In the end i bought expensive water tank paint and painted on top and that stopped dampness coming through.
    Last week I met guy from Rammed Earth Consulting. He is expert on earth building. He explained why i should try lime and clay as waterproofing. I will try soon.
    Nice blog. keep writing when you can.

    1. Hi Erik,

      I have had also problems with cement over the earth vaults/domes. I added some cement water proof additive when I made the mortar mixture (1 part cement, 3 parts fine river sand) so there are no damps or moisture penetrating through the cement but I still get some cracks. The cracks give some additional work because water enters through them. So they need to be filled. Otherwise, even if water enters, since the bricks under the cement are unfired they get wet and after few days dry again. But the danger is if the crack is too big and it rains too much the earth brick could get too wet and break. So it is better to fix the cracks to feel safe.

      Therefore I covered the cracks with more waterproof cement and when I managed to fill them all I painted with a mixture of clay, waterproof white portland cement, salt, iron oxyde colorant, and linseed oil. The mixture I used is one part of white waterproofed cement for 1 part of hydrated lime, salted water and about 4% of linseed over the obtained paint. Linseed oil acts as a paint fixer and also waterproofs a bit more. Besides that I also add some cement waterproof additive. That is a very durable strong paint.

      If after all that I do not get satisfactory results I will think of other solutions. The advantage I have with unfired bricks is that I get no moisture problems because even if water manages to enter it is absorbed fast by the earthen structure and evaporated giving no time for moisture to be formed. Here cement is as expensive as hydrated lime so financially lime has no advantage over cement.

      Waterproofing with clay might be done by mixing it with linseed oil, but I am not sure that it will waterproof it, it will make it water resistant though. But I read that linseed oil has a limited durability so it will require maintenance.

      Another good solution seems to be mixing lime with animal fat, that to make a waterproof mortar. The problem is that I have not managed to find animal fat here. So I might end up making it by boiling fat obtained from a butcher. But I am not sure that will be practical.

      Unfortunately there seems to be no easy answer to the waterproof question, at least not to me. I will have to keep on experimenting until I get some happy results.

      Best !
      Juan

  2. I made a rammed earth grain store. It is 5×8 meters. it has a vault that is quite “flat” 1/10 rise only. Kind of the limit.

    Anyway on this roof I put heavy plastic sheeting. At first i started with rammed earth and then painted with lime. it was hard to ram on a slope. Then 1/2 the building i just threw some soil on top. about 5-8cm. if something grows fine. if not it protects the plastic from deteriorating. will post on my blog soon about it.

    1. That looks very nice and 5×8 is quite big, congrats ! Seems like a nice earth roof.

      I have had a nice success waterproofing my domes with cement. Using a technique from here in Brazil used to make floors (called cemento queimado).

      Basically when the cement is still humid you add some cement powder over it and flatten it with a sheet of metal. That makes it very soft and closes all the pores. It is hard at the beginning to get the technique right but it works out amazing well for waterproofing and it is extremely pretty when you add some pigment in the cement powder mix.

      Then when it is dry you add some wax. It becomes even more waterproof and shines nice. But extremely slippery when wet so a bit dangerous if you want to walk on the roof and its wet.

      Another technique that works quite well is Moroccan Tadelakt, that uses lime, I will probably use that too. The final look is similar to the cement technique.

      I had no time to post because I just pass my time on the construction site but probably I will end up at least posting some pics.

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