Updated: Dec 31, 2022
Rammed earth is both a building method as well as a material. The rammed earth material is a combination of earth, gravel, silt, clay, and lime/cement as a stabilizer combined into a damp mix and is then rammed into forms in order to create a monolithic wall.
Rammed earth construction has been around for many years, one of the most popular rammed earth walls in history is part of the great wall of china.
Rammed earth construction isn't new, but it's going through a renaissance today. This construction method is quickly gaining popularity due to its amazing eco credentials and in some cases, it can be inexpensive.
The world is becoming more eco-conscious and rammed earth is a popular choice of construction.
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Modern rammed earth
Today we are all trying to find ways to be more environmentally friendly. With the way that the planet is going, it is imperative to add some eco elements to a new building project.
Rammed earth is becoming a very popular choice as it's one of the most natural building materials and techniques that you can choose.
Today a lot of rammed earth companies are experimenting with different colors, textures, shapes, and patterns.
Rammed earth is also being used to make furniture and art installations.
Stabilized vs Unstabilized rammed earth
Today a lot of commercial rammed earth construction is stabilized with cement. Stabilized earth walls tend to add on average 2-10% cement to the walls. Cement is added to the walls so that over time the maintenance of the wall is minimal to withstand harsher climates. Also according to the country's building codes, there is minimal compressive strength that is required. So in order to comply with the code cement must be added.
A lot of research is going into ways where cement can be replaced entirely. Hive Earth in Ghana is looking into agro-waste products like coconut husk, and palm kernel ( which we have used in the past for their walls ) as a stabilizer.
Unstabilized walls are also commonly used, but it takes a very skilled and experienced Earth Builder in order to get the perfect mix. Unstabilized rammed earth walls have no cement but can have a natural more eco-friendly stabilizer such as Limestone.
The absence of cement in no way makes the walls not structurally strong but on occasion, unstabilized walls can be more prone to damage over time in harsher climates and may need maintenance after some time.
How is rammed earth made?
Step 1: What soil can be used for rammed earth
Where possible soil is tested on the building site first to see if it can be used to get a good soil mix to build with.
When looking for the soil you want to avoid the topsoil, because it is nutrient-rich. You will find that this will not give the right compressive strength needed to construct a rammed earth wall.
A good mix guideline to go with is roughly 20-30% clay, 70-80% earth, and gravel, then you add your cement or other stabilizers.
You will then need to add your water to the mix, but you don't want it too wet otherwise it won't be able to bind.
Step 2: The perfect mix for rammed earth
The rammed earth mix is one of the most crucial parts of building the wall. If your mix is not correct you can end up with cracks, which can be very difficult to repair.
Rammed earth is a living breathing wall. As soon as you take your form off you may think you have the perfect wall, but cracks may not appear until weeks later.
The correct tested materials are imperative as well as the right consistency of the mix.
When possible try to get the soil from the site we are building on, and depending on the composition of the soil available on site you may have to add a few ingredients in order to make the mix perfect.
For example, if building in a dryer climate the soil there is likely to be dry on the site, you may have to source for a more clay-rich soil to add to the mix to make it good for ramming, if you are building in a mountainous climate the soil there tends to have a high clay content, because of it rains a lot. You may have to source locally for more gravel-textured soil to add the mix.
Rammed earth ball drop test for your mix
There is a basic test that you can do to determine if you have the right mix, this is the ball drop test.
The first step of the ball drop test is to grab some of your mix in your hand.
Secondly, squeeze and compress the mix as hard as possible.
When you have your compressed sample mix in your hand you can drop it from 1m-1.5m high, this is about waist length.
Once you drop your sample it should disintegrate into clumps. In the image below you will see 3 samples. If your sample looks like image 1 the sample is too dry and will not hold once it is rammed, Image 3 the mix is too wet or has too much clay and will not hold once rammed. Image 2 is the best mix.
Step 3: The formwork & Ramming
Once you have the perfect mix you will then pour it into the formwork.
It is recommended to build your form works from scratch as this allows you to be very versatile with our wall design and dimension. Formwork can be made using marine plywood boards.
If you don't have the expertise in building earth forms, there are formworks that you can buy that are premade and ready for assembling, although these can be quite costly.
When building your own formwork you will need to have sturdy strong plywood boards, strong wood, and clamps to reinforce the plywood in order to make the forms tight and strong enough to withstand the compaction of the ramming.
When the formwork is ready you then pour your mix in ready to compact. This is where you can play with designs. The ramming technique determines the lifts, layers, or waves in your walls.
Today you will find rammed earth walls with layers and intricate designs in the walls. To achieve this it is advisable to use manual rammers as this allows for you to have more control of the design and outcome of the wall.
Mechanical rammers are widely used in Earth construction and allow for a faster and more consistent lift design, to use a mechanical rammer you will need to connect it to a compressor.
In terms of the strength of the wall, there isn't any difference in the outcome from manual or mechanical ramming.
Would you build with rammed earth?
Building with rammed earth can be laborious but the beauty in the finished product is a result of the labor in finding the right mix, building your form, and ramming. Not to mention the many advantages rammed earth has as compared to conventional building materials and methods.
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