Mud: Fact File

Abbie Harby
"If we were meant to stay in one place we'd have roots instead of feet" and so I move - in cities, between cities, up mountains (and back down again!). And all that using my feet as much as possible - the first mode of transport known to man and the cheapest! I love the outdoors and being in green space. I'm passionate about trying to protect and improve all that we've got and all that we could have to give every single part of nature the best life possible.

Half of the world’s population is living in mud constructions. And we can understand why. Take a look at the following facts, primary building methods, and the main uses of earth in construction to find out how the very substance beneath our feet can be utilised in buildings and why it could be vital in finding sustainable solutions.

While some of you might feel that mud is only used in far-flung nations with little option other than to construct using earth, we’re here to bust that myth and fling it like a mud pie. The truth is mud has been used for thousands of years in both rural and urban settings. And it’s not just suitable for housing: 15% of the architectural masterpieces on UNESCO’s World Heritage List were built using earth. However, don’t be fooled into thinking that this is an outdated option or one that won’t hold up against the elements. There are actually some buildings which are over 150 years old and still standing proud. Keep reading to find out more.

Types of Mud Construction and Their Uses

Remember, the following techniques can also be used in combination. There are lots of different types of earth even within a single country and region. First, investigate your construction site (i.e., where you will be building): dig a hole to look at the types, proportions, and depths of each earth sort. Just a note: if wet soil smells slightly musty, it could be a sign that it contains organic matter, which should be avoided. The supply chain will depend on what is available, what you need, and where you can get this from.

There are numerous other earth construction techniques, but here’s a look at just six to let your mind start wandering:

1. Rammed Earth

This technique uses earth, chalk, lime, and gravel. While it can be hard work to construct without using machinery (powered rammers), the method is generally simple. Rammed earth walls, also called pise, are made by ramming or compacting moistened subsoil in layers into position using temporary panels. The final step is the removal of the framework.

The final build will meet sustainability goals (if materials such as cement are left out) and also be fire-resistant, strong, and durable. In fact, rammed earth constructions are so strong that parts of The Great Wall of China were built using this method. It is even loadbearing, allowing the construction of multiple floors.

Rammed earth constructions can already be found all over the world in a wide variety of climates. You simply have to use local soil and be satisfied with the building design that best suits your region’s weather conditions. Be aware that not every type of soil is suitable for rammed earth structures.

2. Moulded and Compresed Earth Bricks and Blocks

To create the standard mud bricks used in construction, earth is combined with water to form a mixture which is poured into moulds. These are then dried in the open air. It is also possible to add straw or other fibres which have a high tension in order to prevent the bricks from cracking. To build a structure, mud mortar is used to join the bricks.

Mud brick constructions can be extremely simple. Therefore, even beginners and self-builders can use this technique.

Mud bricks can be used to make walls, vaults, and domes.

3. Cob Building or Stacked Earth

The term cob means ‘lump’ or ‘rounded mass’. This technique uses moist subsoil combined with sand and unchopped straw. The straw is employed to reinforce the binding element and to prevent cracking. A bit like bread, the mixture is kneaded and turned into loaf shapes. All of this is to be done by hand which has the added advantage of being able to shape and design the building however you want. The technique is super simple which is great for self-builders, however, it does take longer than other natural material building techniques.

The walls are constructed in layers by stacking the mud loaves, allowing each layer to dry and harden before adding the next. These walls can either be left unfinished or covered with clay or lime plasters. Bear in mind that if using this technique in wet climates, an unfinished wall will need to be protected by eaves, overhang, or some kind of shelter.

Cob building is perfect for creating organic shapes, such as curved walls, arches and niches.

4. Light Earth or Straw Clay

As a combination of cob and rammed earth, this method means the final structure is lighter than cob and has a better insulation value, though it isn’t as strong. It must, therefore, be used as infill with a timber frame.

Fibrous materials, such as loose straw, are covered in a clay slip which is rammed tightly in layers into the timber frame. Before plastering, walls must be left to dry. This technique can also be used as roof insulation between rafters or underneath earth floors.

5. Adobe

Adobe is a sun-dried clay brick: one of the oldest building materials used by man. Due to the drying process, they require a period of warm, dry weather to ensure they are properly structured. This technique sees thick mud that is easily workable being mixed with straw. It can then either be shaped by hand or by using wooden moulds. The adobe mix can also be used to join the individual bricks together, meaning the wall structure is simple to assemble.

The durability, high thermal mass of the structure, and the low investment in basic materials required are all advantages. Nevertheless, in the wrong location and without appropriate reinforcement, adobe constructions can be easily damaged by earthquakes. Additionally, the amount of usable interior space is lower than other techniques as adobe bricks take up a fair amount of room.

6. Wattle and Daub

This is one of the most common techniques for wall infill. Timber is used to create a woven lattice which is then plastered with an earth mixture containing wet soil, clay, sand, animal dung, and straw. The name says it all here as it describes the two stages of construction: wattle is a woven structure of small plant elements (e.g., tree branches, bamboo, reeds) which all firmly hold together; daub refers to the mud mixture which is similar to the one used for mud bricks with dung as the organic binder. Covering the wattle with daub is done by hand. To finish, the wall can either be smeared in a final layer of daub or be whitewashed with lime.

In comparison to other earth techniques, wattle and daub is actually very thin and flexible, though, as a result, its’ thermal mass properties are not as good.

Mud Around The World

Yemen Towers, Yemen

Interestingly, in Yemen, the height of the towers indicates the wealth and power of its owner: the higher the tower, the wealthier and more powerful they are.

Construction begins by digging deep to find firm soil, where a layer of animal droppings is deposited, followed by salt. Timbers are positioned parallel to the walls with stones in the spaces. The walls are constructed in this way up to street level, after which mud bricks that have been dried in the sun are used to build up to six storeys. The walls therefore become thinner higher up the structure.

New Gourna Village, Upper Egypt

The design of earth buildings developed by the architect Hassan Fathy in 1946 showed how the traditional elements of Arab urban architecture could be combined with the use of mud bricks. His aim was to construct a sustainable and socially conscious village using locally sourced materials while respecting the ancient techniques.

The entire village is an interconnected and incredibly strong structure. The houses in this village are all topped with a dome functioning as a heat regulator. This element along with traditional methods provide exceptional ventilation. The versatility of earth in design can also be witnessed: arches, domes, square and rectangular forms, all carved out of mud. Proof of the aesthetic appeal is how Fathy carved the windows in various shapes which create shadows on the ground that change throughout the day as the sun changes position.

Rudrapur, Bangladesh

A village school built in Bangladesh shows the capability of earth to be used in combination with bamboo to construct a stable, sustainable, non-residential building. Here, mud loadbearing walls with bamboo framing were the chosen method.

Three layers of bamboo posts were bound together for the floor beams which are connected to the mud walls at both ends. Conventional engineering ideas and steel dowels were used to connect the layers of bamboo. Mud bricks formed the foundation and straw was additionally mixed into the clay and sand. The rammed earth of the walls was rendered in such a way that it exposes the straw reinforcement which also meant that no further rendering/finishing was required.

The climate, availability of materials, and lack of electricity in the village encouraged the architects to insert apertures in the mud wall as well as slatted walls. The material and these design elements mean the school remains cool in the hot summers but also pleasant in the winter.

Lyon, France

But it’s not just in arid climates that mud construction methods flourish. France is one of the few places where there are examples of all four of the main earth building techniques: rammed earth, adobe, torchis cob and bauge cob. Earth construction isn’t shy of the urban world, as the structures in France are proving with a variety of bourgeois homes and large cities or districts being constructed using mud. To top it off, 15% of France’s architectural heritage is built from raw earth.

Earth housing in Lyon, France
Image credit: Unsplash / Christian V

In the city of Lyon, you can find rammed earth structures predominantly on the border areas where rural meets urban. One such example is the district of Croix-Rousse. While rammed earth constructions are usually low-builds with no more than two or three storeys, in Croix-Rousse buildings can have up to seven storeys.

Hollow terracotta tiles usually cover Lyon’s rammed earth buildings. The frame is made only of beams (horizontal, longitudinal, or vertical) as there are typically many shear walls (meaning they are built with the purpose of being able to withstand forces, such as wind and earthquakes). Walls are constructed by taking earth directly from the ground without requiring extra water. In Lyon, walls with a mixed composition – e.g., with rubble, brick, and pebbles – are not uncommon. Mortar connects all of the layers that form the walls. Usually, rammed earth constructions in urban settings are coated to protect them from moisture and improve the durability of the earth walls.

Advantages

  • Mud bricks may have the least significant environmental impact of all construction materials for multiple reasons:
    • They should be made only with clays and sands, no living soil.
    • Although they require a lot of water to produce, they need very little energy.
    • Their embodied energy is probably the lowest in comparison to other materials. This would only rise if other ingredients, such as cement, are added, if it travels long distances, or if significant energy is generated in the mechanical processes associated with the construction.
  • Construction using mud/earth can work on a large scale. i.e., not just for single storey houses, but also multiple storey high builds.
  • Mud bricks, for example, can be used to construct loadbearing structures.
  • Mud as a material has a high thermal mass meaning it can absorb, store and then release the heat again later on. This is due to its high density.
  • As a result of this, you can save money on operating costs in summer as there is less need for air conditioning.
  • The high density also means mud constructions have good acoustic insulation. Mud brick walls can have almost the same sound insulation quality as usual masonry structures.
  • Moreover, construction costs when using earth as the primary material can be kept very low. In general, if local resources are used, mud can be a very cost-efficient option. It also depends on the amount of wall to build, the design and the height.
  • Highly fire-resistant.
  • Mud bricks (or small mud units) can offer a lot of flexibility in terms of design.
  • This material can store volatile organic compounds which, if otherwise released, could be harmful to humans and the environment.
  • Mud is a breathable material, offering a healthier indoor air quality. For instance, at 50% humidity (an easily attainable level when building with earth), it is more difficult for bacteria and mould to grow and the air is better, in particular for asthma and allergy sufferers.
  • It can also be used decoratively, offering the choice of a flat or a very colourful and textured finish.
  • It requires very little energy to manufacture. In fact, the only energy it needs is the sun.
  • Using earth in construction also fits perfectly into circular building and the circular economy structure we should be advocating. The bricks can just be turned back into earth once the building reaches the end of its life.

Disadvantages

  • Mud and earth can be vulnerable to water damage and easily destroyed by wind, rain, and flooding if not protected and maintained well enough.
  • Low moisture resistance can be a breeding ground for bacteria if not looked after. This also means that the material must be looked after and protected from the weather, in particular from driving rain. One way to do so is by having deep-set eaves.
  • Rammed earth structures in particular can stain easily.
  • Mud has a low tensile strength and can come apart easily, making mud walls susceptible to rodents and unwanted visitors.
  • This also means mud roofs are difficult to construct and will usually need to be combined with another material in order to do this.
  • Therefore, mud/earth buildings require regular maintenance.
  • Some mud brick recipes contain bitumen, which may release hydrocarbons. Ideally, the earth should be used as close to its natural state as possible.
  • While earth is ideal for keeping buildings cool in summer, this can prove problematic in winter. The low thermal resistance means a lot of heat is lost through the walls as air cannot be trapped in the structure.
  • This technique requires quite a lot of work, in both construction and maintenance.

Mud in a Nutshell

Now you’ve witnessed how simple, sustainable, and accessible building with mud can be, it’s time to seriously stop and consider whether it could be employed for your next construction project. We all need to be playing our part in constructing urban environments in a healthier, renewable, and longer-lasting way and what could be better than using one of the many materials that mother nature provided us with? Happy digging!

If you want to find out more about constructing with natural materials, take a look here or at some of the other natural building materials on offer:

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