Rammed earth is one of the most sustainable and green building materials.
This material has been used in construction for centuries thanks to its high strength, durability, and thermal mass.
However, before using this material in your construction project, you might be wondering just how long does rammed earth last and whether it is sufficiently durable for building your home.
Rammed earth is a durable material that lasts more than 1,000 years. The durability of rammed earth may vary depending on the soil type, amount of compaction, particle size, and the type and amount of stabilizer used. Well-cured stabilized rammed earth lasts longer than its traditional counterpart.
In the rest of this article, I’ll explore rammed earth construction, including floors and load-bearing walls.
I’ll also discuss whether rammed earth is stronger than concrete.
Keep reading to learn more about rammed earth as a construction material.
Rammed earth can be used to make floors as well as walls. We cover this use case in our article “Can You Use Rammed Earth For Floors? (See These 5 Examples).”
Generally, rammed earth walls can last anywhere from 20 to more than 1,000 years. The lifespan of these walls depends mainly on the soil type and composition, curing, and the amount of stabilizer. Using a stabilizer such as lime or cement increases the lifespan of rammed earth walls.
Let’s look at how soil type, curing, and stabilizer affect the durability of rammed earth walls.
Rammed earth is made from earthen materials, including soil, gravel, and silt.
Soil is an essential ingredient and contributes to the strength of the rammed earth walls.
According to California Polytechnic State University, soil composition is an important factor in determining the compressive strength of rammed earth walls.
According to this study, the higher the clay content of the material, the higher its strength, although the authors note problems with the curing process for weaker samples.
Sandy soil should make up the highest portion (60-70%) of the mixture, with the rest being made up of clay, gravel (15-20%), and silt (10-15%). This composition helps to improve the strength and durability of rammed earth.
While sand and gravel enhance the material’s structural strength, partly by interlocking within the mixture, clay soil helps to bind the particles together, filling in the gaps between the larger particles.
You should carefully test the composition of these materials before beginning construction to improve the lifespan of your rammed earth walls. Site-specific testing of rammed earth samples is important because soils can vary considerably across short distances.
The curing process is essential for increasing the lifespan of rammed earth walls. Traditionally, curing involves moistening the mixture and drying it for sufficient compaction. The strategy aims to reduce cracking, shrinkage, and water absorption in the wall.
The rammed earth wall hardens during the drying process, increasing its compressive strength to a maximum of 4.3MPa (620 psi).
In modern rammed earth construction, the earth is often mixed with calcium carbide and fly ash before curing. When this is done, the curing duration impacts the material’s durability. For instance, one piece of research found that curing these materials for 60 days made them 25 times stronger.
Stabilizing rammed earth involves adding cement, lime, or other stabilizing agents to the material. The stabilizer helps increase the strength and durability of rammed earth walls by improving their compaction ratio, reducing water absorption, and preventing shrinkage.
Although lime stabilizes rammed earth, most people prefer Portland cement due to its excellent load-bearing capacity.
As a rule of thumb, 5 to 10% cement by weight is sufficient for the best results. The mixture should be cured for at least 28 days to make it stronger and more durable.
Rammed earth is not stronger than concrete. While traditional (unstabilized) rammed earth has a compressive strength of about 2.68 MPa, concrete has a compressive strength between 17 MPa and 28 MPa. This shows how strong and durable concrete is as a construction material.
Cement-stabilized rammed earth (CSRE) has a higher compressive strength of about 9.30 MPa.
The higher compressive strength of CSRE comes about during the curing process when the cement undergoes a hydration reaction that forms interlocking crystals within the CSRE matrix, binding the whole mixture together into a solid rock-like material.
The hydration reaction results in CSRE’s improved strength, durability, and water resistance, which make it more suitable for construction than its unstabilized counterpart.
Although concrete is stronger than rammed earth in terms of compressive strength, the focus is shifting to rammed earth due to its sustainability and eco-friendliness.
While concrete production degrades the environment and consumes a lot of energy, rammed earth is made of natural materials generated without so many adverse environmental effects.
Load-bearing walls must have high strength and stiffness since they support the weight of the upper floors and roof.
Rammed earth walls can be load-bearing since this material’s compressive strength can support the weight of the overlying materials.
However, its load-bearing capability is limited to 2 to 3 stories high. Beyond this, you’ll be risking the stability of your house, meaning it won’t comply with standards applied to industrial materials.
As discussed, you can enhance the strength of rammed earth walls with stabilizers such as Portland cement and lime to make them suitable for load-bearing applications.
From the above discussion, it’s clear that unstabilized rammed earth walls have low compressive strength and are sensitive to water.
Due to these features, the following are some measures to enhance your rammed earth project’s lifespan:
- Use stabilizers: Add cement or lime in the appropriate quantity to the rammed earth mixture. Besides enhancing the material’s compressive strength, stabilizers help reduce the water absorption rate of the material.
- Proper curing: To ensure maximum strength and water resistance of the stabilized rammed earth walls, cure for at least 28 days.
- Build a suitable roof: Ensure the roof has proper drainage and is water-resistant. This will keep the walls dry, enhancing their durability.
- Check the basement: Ensure to keep the capillary rise of water through the basement in check to prevent moisture from seeping into the walls. A capillary break layer and vapor barrier will help with this.
How Long Does Rammed Earth Last? Final Thoughts
Earthen structures can last centuries when appropriately cured and combined with a suitable stabilizer like Portland cement.
Besides curing, the composition of the raw materials for making rammed earth is another crucial factor that affects durability. As a rule of thumb, sand should make up the highest composition in the mixture, followed by gravel and clay.
Finally, take steps to keep the basement of a rammed earth building free of moisture to prevent the walls from weakening due to water being drawn up them through capillary action.
A similar construction material to rammed earth is compressed earth blocks. If you’re interested in learning more about them, read our article, “All About Compressed Earth Blocks: Pros And Cons To Consider.”