What Is a Rammed Earth Wall? (How They're Built - 6 Steps)

Have you ever heard of a sustainable construction material made entirely of dirt?

No, we’re not talking about a shoddy sandcastle on the beach, but rather, an old-age technique called rammed earth construction.

Rammed earth walls have been used for thousands of years and can be found worldwide – from ancient China to the modern-day United States.

But what exactly is a rammed earth wall?

A rammed earth wall is a wall built by forcing (ramming) a mixture of subsoil with gravel, clay, sand, silt, and a stabilizer (if any) into formworks. For a sturdy wall, these aggregates are mixed in the proportions of 30 to 40% clay soil and 60 to 70% gravel, sand, and fines before ramming.

In the rest of this article, I’ll discuss how rammed earth walls are built and insulated. I’ll also discuss their R-value to help you understand if they are ideal for your insulation requirements.

Let’s dive in!

Table of Contents

The Process of Making a Rammed Earth Wall

Making a rammed earth wall is not just a matter of shoveling dirt into formworks. It’s an art that requires skill and attention to detail for a sturdy wall suitable for load bearing.

Here is a step-by-step guide for making a rammed earth wall:

Step 1: Soil Selection

A man's hand holding soil and allowing it to run through his fingers. — Choosing the right soil is essential for a strong rammed earth wall.

The type of soil you use determines the wall’s stability. An appropriate soil must meet the compressive standards for the wall.

It’s advisable to avoid topsoil as much as possible. Topsoil contains organic matter that will decay and interfere with the wall’s structural integrity.

Moreover, the amount of organic matter and other particles in topsoil creates a conducive environment for pests like termites to thrive. These pests can get to the wooden sections of the house and cause severe damage.

Subsoil is the best option for rammed earth walls. The soil should be excavated from a depth exceeding 1 meter below the ground surface for the best results. This way, you can rest assured that the soil doesn’t contain organic material that can affect the wall.

Step 2: Soil Preparation

The soil selected needs to be prepared before use.

Soil preparation involves ensuring the right proportion of sand, clay, silt, and gravel. A rule of thumb is to have 30-40% clay and 60 to 70% sand, gravel, and other fine particles.

A mason jar test is a simple way to determine the soil’s percentages of sand, clay, and silt.

Performing a Mason Jar Test

Two photographs of a Mason Jar Test showing jars full of water and soil. The jar on the left has been allowed to settle for 24 hours, and the jar on the right has settled for 4 days. The layers of material of different particle sizes are clearly visible. Coarser-grained materials settle to the bottom, with finer-grained particles like silt and clay at the top. — A Mason Jar Test. The layers of material of different particle sizes are clearly visible. Coarser-grained materials settle to the bottom, with finer-grained particles like silt and clay at the top. Image courtesy of Rooted Revival.

Here is the procedure to perform a mason jar test:

Fill the jar 1/3 of the way full with the selected soil.
Add water and dish soap almost to the top of the jar and shake well.
Leave the mixture to settle for between 48 and 72 hours.
Observe the distinctive soil horizons. The bottom layer is made up of sand; silt will form the middle layer, while clay will be at the top.
Use a ruler to determine the total height of the soil mixture layers.
Measure the heights of sand, silt, and clay layers with a ruler.

Once you have all the measurements, use the formula below to calculate the percentages of clay, sand, and silt:

Percentage of sand: {(Height of sand)/(total height of the mixture)}✕100%.
Percentage of silt: {(Height of silt)/(total height of the mixture)}✕100%.
Percentage of clay: {(Height of clay)/(total height of the mixture)}✕100%.

Step 3: Mixing the Soil

Once you have the right soil proportion, it’s time to get to work by mixing it into a paste.

Start by adding water to the soil in small quantiles. Once you get a homogenous paste, add enough water until it reaches the desired consistency for rammed earth walls.

The paste should be neither dry nor too sloppy.

It’s worth mentioning that stabilized rammed earth walls are common in modern-day constructions due to their high stability. A stabilizer, usually cement or lime, is added to the rammed earth and water mixture.

If you want a stabilized rammed earth wall, adding 5 to 10% cement into the mixture is advisable.

Step 4: Formworks

Wooden formwork being used to construct a large rammed earth wall. An excavator lifts the rammed earth mixture to the top of the forms before compacting. — Wooden formwork is a popular option for building rammed earth walls. Image courtesy of ourfarmadventure on flickr.

Formworks are used to shape and hold the mixture when ramming. Generally, formworks are made from wood or metal.

Formworks are essential to hold the mixture as it is compressed during ramming and undergoes the initial curing process. This is especially true when building curved rammed earth walls. In this case, you’ll need curved formworks that can be made from bamboo wood.

A rule of thumb is to ensure the formwork is smooth and straight for a solid, stable wall.

Additionally, the formwork must be firmly fixed onto the ground with stakes or nails to prevent shifting.

Step 5: Ramming

Finally, after all the preparations, ramming begins.

The rammed earth mixture is filled into the formwork layer by layer until you reach the desired height.

Usually, filling each layer up to 10 centimeters (3.94 inches) is recommended. Once you attain this height, use a ramming tool like a stamper or a mallet to compact the mixture to between six and seven centimeters (2.36 and 2.76 inches).

Compacting the mixture involves continually lifting the ramming tool and letting it hit the soil.

Repeat this process until you get to the top of the mold. Once you reach the top, remove the mold and set it on the created wall to increase its height.

Alternatively, you can set the mold on the side to elongate the wall horizontally.

Step 6: Finishing

A worker gives the finishing touches to an impressive rammed earth wall with a spray bottle and cloth. — Rammed earth walls can look beautiful, so painting them seems like a shame. Instead, sealing them with a coat of wax can protect them while retaining the visual appeal. Image courtesy of Rammed Earth Works.

Now that the wall stands firm, it’s time to add the finishing touches. However, you should allow the wall enough time to cure before finishing.

The curing period is at least 28 days for cement-stabilized rammed earth walls.

The rammed earth wall can be left as is or painted to give it a cleaner aesthetic appeal.

If you want to paint, clean off loose particles and remove any irregularities with a trowel or chisel before painting.

If you live in a moist environment, it’s recommended to seal the wall with a coat of paint or wax. This protects it from water damage and erosion.

How Are Rammed Earth Walls Insulated?

A worker wearing overalls and protective gloves installs rigid foam board insulation against a rammed earth wall using mechanical fasteners. — Installing rigid foam board insulation using mechanical fasters.

Unfortunately, rammed earth walls have limited insulation qualities but have high thermal mass. Its high thermal mass means it is good at absorbing heat during the day and releasing it at night, which helps to even out large diurnal fluctuations in temperature.

However, insulating your rammed earth wall is usually necessary, especially if you live in an area with extreme temperatures. This will help conserve energy by lowering the demand for heating and cooling.

Rammed earth walls are often insulated with rigid foam-based insulations. Some options include:

Expanded polystyrene (EPS)
Extruded polystyrene (XPS)
Graphite polystyrene (GPS)
Polyisocyanurate

Rockwool insulation is also an excellent rammed earth wall insulator.

The following are the general steps to insulate a rammed earth wall:

Choose the appropriate insulation R-value: Consider your climate zone for an appropriate R-value. The International Energy Conservation Code (IECC) is an excellent guide for climate zones.
Choose a type of rigid foam insulation: Check the above rigid foam insulations and choose one that aligns with the R-value requirements for your specific climate zone.
Install a drainage plane: Before installing the insulation, you should install a drainage plane to prevent moisture from getting trapped behind the insulation. You can use a plastic drainage mat or a layer of building paper.
Cut the insulation to size: Use a saw or knife to cut the insulation according to the wall length and width.
Secure the insulation: Apply a bead of adhesive to the back of the insulation panel and press it firmly against the rammed earth wall. Use mechanical fasteners like TEC and PMF Plastic nailsto secure the insulation.
Seal the joints: Use insulation tape or caulk to seal the joints between the insulation panels. This will help prevent air leaks, improving the building’s energy efficiency.
Finish the wall: Once the insulation is installed, you can finish the wall with drywall, plaster, or stucco.

What Is the R-Value of Rammed Earth?

The R-value of rammed earth walls is 0.4 per inch. This is a low R-value compared to other sustainable building materials like straw bales and cork.

The high thermal conductivity is the main reason for the low R-value of rammed earth and explains why many people insulate these walls for a comfortable indoor environment.

Final Thoughts

Rammed earth walls are an ancient and sustainable building technique that has stood the test of time.

Besides being environmentally friendly, rammed earth walls are strong and durable, making them ideal for load bearing.

The only downside of these walls is that they’re poor insulators. Therefore, you must insulate them for a better indoor environment.

As an interested homeowner, you should know how long rammed earth lasts before embracing it. Check out this article discussing the durability of rammed earth and whether it’s worth it.

What Is a Rammed Earth Wall? (How They’re Built – 6 Steps)