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What is Adobe ?
Production, Application & Features
Adobe is a composite building material made with soil and straws. Needed amount of water is added to soil and straws which is traditionally crushed and squezed by foot, to mix the materials creating mud. In some regions, dung is used instead of straws. Straws are used to bind the bricks together. It also allow the bricks to dry equally. Some experiments show that using straws in adobe bricks make them more resistant for cracks. Dung is mainly used to avoid insects.
The mixture is then casted into wooden frames ( usually 30cm x 45cmx 6cm).It is compressed within the wooden frames to prevent the gaps, making it dense and strong. Excess mud is glanced off the frames to make a flat surface for the bricks. Wooden frames are removed and adobe bricks are left to dry in a flat surface, under the sun for a few days.
It is a low-cost and easy to make material which was widely used all around the world extensively in Egypt, Sudan, Middle East and Asia Minor. As it is an earth material, it is suitable for semi-arid climates where summers are hot and dry and winters cold and wet. It has a high thermal mass which is defined as the ability of the material to absorb heat. It helps to stabilize the inside temperature of the buildings.
Main raw materials of adobe can easily be found locally. Soil types and colours depends on the locality and that is the main reason to see different coloured adobe buildings in different areas.
Load bearing walls made from adobe bricks are usually 45-50cm wide. Minimum width should not be less than 30 cm. Adobe walls carry their own weight into foundations so there is no need for other sturctures to carry the load of the walls. Usually, 80-100 cm high stone walls are built as a base for the adobe walls to prevent the affect of ground humidity on adobe bricks.
As there are not any other structures to carry the adobe walls, ground is dug for the footings. The depth of the excavated area depends on the local characteristics of the ground and the frost level of the soil. The mistaken setup of the foundations might cause cracks on the walls.
Courses of adobe bricks are lined horizantally and binded together with mud mortar to form the adobe walls. Mud plaster which is a breathable material that can allow the moisture of the adobe walls to evaporate; is used to plaster the first layer of the adobe walls. Fine grained straws are added where straw fibers increase binding and to obtain a smooth surface. Mud plaster is a durable material but the final finish of the wall is made by plastering lime based paste which is a water-resistant material to protect the structural characteristic of the adobe.
As it is an earth material, annual repair is recommended. Worn surfaces are replaced by mud mortar and plastered again. This process is usually carried out during autumn.
In adobe houses, the width of the buildings do no exceed 4m (13ft) generally. The spaces are mostly rectangular and in some cases they might be square shaped. It is recommended to build maximum two storeys with adobe.
Ceiling beams which were commonly wood, are placed parallel to the short side of the rectangle with 30-40cm intervals. For these beams, cypress tree was commonly used in Cyprus. Bushes or reeds were placed above the beams or in some cases reeds in the form of mats might be used if available. On top of this layer, 20-25 cm thick clay is casted and compressed by a stone roller. This type of roofs need annual repair, which usually carried out in autumn. If the roof is build with a slope, tiles are used to cover the clay layer. This will reduce the abrasion of the clay and reduces the need for maintenance.
Use of Adobe in Cyprus
Adobe is a common building material in Cyprus from early ages. Building materials might vary in different regions, such as Kyrenia and Paphos (which are coastal regions of the island) stone was used to build shelters. In the plains and foothills, adobe was widely used. The use of the materials depended on the regional availability and climatic factors.
As adobe is an insulating material, majority of the houses were build using adobe. Mesaoria valley which is located between Kyrenia Mountains in the north and Trodos Mountains in the southwest of the island, is an aluvial plain where most of the adobe buildings can be seen. Reports on soil surveys in Cyprus shows that there are mainly two types of soil in the island. One is ‘deep soils’ which can be found in plains and second one is ‘shallow soils’ which can be found in mountain and semi mountain areas.
‘Deep soil’ results show that %60 of the soil in plains is clay. Large amount of the plain lands is calcareus with calcium carbonate content up to %40-60. Limestone is a sedimentary rock which includes high levels of calcium carbonate . Limestone is processed in different stages to produce lime.
Including insulation features of adobe, suitable ingredients can be found locally around the island which are soil with high clay content, and limestone to produce lime. Adobe bricks are dried under sun where limestone and roof tiles are baked in local furnaces by using wood or fuel. This makes adobe a sustainable and natural material. Limestone was also used to build terrace walls.
Nicosia is located in the Mesaoria valley where adobe buildings can widely be seen. After the declaration of independence of the island in 1960, concrete buildings started to rise over the island. Nowadays, small amounts of earth buildings are built around Cyprus.
Cyprus is hot and dry during summer where the need for ventilation is highly demanded inside the buildings. Privacy was an important factor on shaping the traditional house design of Cyprus where windows were built above eye level to keep the privacy. Windows on adobe walls were made by placing wooden lintels on top of the openings to support the bricks above.
Terra rossa soil is present in some areas of Mesaoria plain which is a reddish brown soil. Colour of adobe bricks might vary in different regions of the island.
Partition walls inside the buildings were usually built with light timber-framing filled with rubble or plaster. As adobe is a heavy material, it was used to built the external walls only.
Testing adobe samples from the Davies House
I scratched a very little amount of adobe from the external wall of the Davies House. It was easily crumbled into small pieces mainly because of the low strenght of the wall. My main aim to test these samples is to find out and define the ingredients of the adobe used in this particular building. My intention was also to find out the age of the material if possible.
First stage in the laboratory was to look at the samples under a microscope. A small amount from the sample was taken and placed on a slip. Soil and straw particles were clearly seen but it was hard to identify the materials clearly. As they were mixed and mostly binded with each other, I need to separate the ingredients.
The way of separating the composite material is to mix the desired amount of sample with water and leave it for one day. By this way, dense and heavy materials which are soil particles in this case will sink; where the light materials will float on the liquid which are the straws that has lower density than water which makes them float.
Half of the adobe sample is grained by using a hammer. A fine grained powder was obtained. 5gr of the powder was weighted by a sensitive weighting scale. It was put inside a glass beaker and 200ml of distilled water added to the sample. The mixture was stirred manually for a few minutes and then placed on the magnetic stirrer hotplate. The feature of this hotplate is that it has a magnetic field and if a magnet is placed inside the solution, the magnet will make a circular spin and stir it. A magnet was put inside the solution and left to stir and heat for approximately 15 minutes. I used a thermometer to measure the temperature of the solution and around 42°, closed the hotplate. By stirring and heating, I achieved a well-mixed solution. After a few minutes, I covered the beaker with a flat glass dish and leave it for a night.
Through research I found out that lime was used to plaster the adobe walls. There are some evidence on the walls of the Davies House but to prove that, I used hydrochloric acid. Lime is a material that contains calcium carbonate. The reaction of hydrochloric acid or any acid with calcium carbonate will end up with producing carbon dioxide which can be seen by naked eye as air bubbles.
In order to prove that lime was used in Davies House, I put a little amount of adobe powder in a test tube. Couple of drops of hydrochloric acid is enough to see the air bubbles. As a result, reaction of the acid with the adobe sample is positive which proves that lime was used in this building. It also raises another question that if the type of soil in Mesaoria contains %40-60 calcium carbonate, does the reaction with the acid is because of the type of soil used in adobe bricks?
The mixture was left for a night. Dense and heavy and insoluble materials sink at the bottom of the beaker, where light ones float on the water. Water is not clear which can be defined that some of the soil was dissolved in water. A filter paper was placed inside a funnel and an empty glass beaker was placed below. In order to collect the floating materials, I poured the water into the funnel slowly without disturbing the bottom. It was hard to collect all of the floating material so I used a metal spatula to collect the remaining from the mixture. The water was filtered from the funnel, leaving the straw particles on the filter paper. Straws were collected from the filter paper and was put together with the ones that were collected manually inside a porcelain crucible. I left them dry in the room temperature for 15 minutes and put them in the oven for 35-40 minutes. They were dried completely and ready to weight.
I changed the filter paper and poured the remaining water into the funnel. Some of the insoluble materials remained at the bottom of the beaker so I collected them by the help of the metal spatula and put inside another porcelain crucible. Water was filtered after 2 hours from the funnel and I collected the materials from the filter paper and place them inside the crucible. Same process was made to dry the materials. I let them dry in room temperature for a while and put them in oven for 40-45 minutes.
I weighted the obtained materials separately by using a sensible weight scale.
Insoluble Materials (soil,pebbles) : 4.56gr ( Wâ‚ )
Floating Materials (straws) : 0.06gr ( Wâ‚‚ )
Exact amount of the whole sample was 5.04 gr. The formula below will give the percentages of the materials in the sample.
Wâ‚÷ Total Weight x 100 = %..
Wâ‚‚÷ Total Weight x 100 = %..
Insoluble Materials (soil,pebbles) : % 90.48
Floating Materials (straws) : % 1.19
As the water was not clear after leaving the solution for a night, it is defined that there are soluble materials in the mixture. So if soluble materials are Wâ‚ƒ ;
Wâ‚ + Wâ‚‚ + Wâ‚ƒ = 5.04 gr
Wâ‚ƒ = 0.42gr
Wâ‚ƒ = % 8.33
Experiment shows that most of the adobe material is soil . Straws were used to strengthen the binding of the bricks. The amount of straws in 5gr is 0.06gr which is very few. As the building is old and neglected, straw particles might have been disapeared or decayed within the soil through time.
Original ingredients of the adobe is soil, straws and water. In order to prove that the separated materials from my sample is straws, they need to be identified under a microscope. They are most probably straws but there is a possibility that they might be timber.
Timber and wooden materials are identified under a microscope by looking at the layout of the cells. Wood are mainly classified in two groups which are soft and hard woods but the layout of their cells are similar. If horizantal rays of cells are seen under a microscope, it is a wooden structure.
Next step of identifying the straw particles will be to look under a microscope after cutting very thin sections of the pieces. One way of guessing the age of the wood is to identify the fungus formations within the material. The dimensions of the fungus might refer to its age. This can be done by using a microscope but only if the separated particles are timber/wood but not straw.
Straws under the microscope :
Soil particles under microscope :
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