If you’re reading this, I’m sure you’ve already done your research on rammed earth and are familiar with its benefits. But if not, let me mention a few. it’s one of the most sustainable ways of building, thermally insulative, soundproof, eco-friendly, and aesthetically beautiful. I might be biased since I work with rammed earth, but there’s something incredibly calming and zen about being inside a rammed earth building. Its soundproof nature creates a cocoon-like ambiance, almost like nature itself is giving you a warm hug.
One frustrating aspect of working with earth, especially if you're a beginner, is that it can be prone to cracks. Hairline cracks are completely normal and generally nothing to worry about. However, large vertical cracks can cause problems and are a real eyesore.
I’ve been asked to fix cracks many times on other projects and despite my experience, I still occasionally deal with them. Over the years, though, I’ve become quite skilled at crack repair, if I do say so myself. But here’s the thing, even if you’re a pro at fixing them, to a trained eye, a repaired crack can often be spotted. While most cracks can be dressed to almost undetectable, it’s always best to prevent them in the first place.
Understanding Rammed Earth Cracks
Cracks in rammed earth walls can vary in size and severity. Hairline cracks are common and usually form as part of the natural drying process, often due to slight shrinkage in the material. These are generally not a cause for concern. However, large vertical or horizontal cracks can be more problematic and can arise from issues such as improper material composition, inconsistent moisture content, or uneven drying. While small cracks are a natural occurrence in rammed earth, larger cracks can compromise the structural integrity and aesthetic of the wall, making it important to address their root causes.
How to Prevent Cracks in Rammed Earth Walls
Here are my top 5 tips for preventing cracks in your rammed earth walls. While these tips address common causes of cracks, it's important to note that other factors, such as foundation issues or the terrain of the land, can also contribute. However, these are the most frequent and effective methods to help prevent cracks from occurring in your walls.
Testing Your Materials Beforehand
Testing your soil composition in a lab is essential to ensure the correct balance of clay, sand, and silt. The right mix minimizes the chances of cracking, as too much or too little of any component can affect the wall’s structural integrity. Proper testing ensures a solid foundation for the rest of the building process.
2. Ensuring Proper Moisture Content
The moisture content of the soil plays a critical role in rammed earth construction. Too much moisture can weaken the mix, while too little can cause the wall to dry unevenly, leading to cracks. A simple way to test the moisture content of your mix is by using the ball drop test. To do this, grab a handful of the mix, squeeze it in your palm, and then drop it from waist height. If it breaks apart into small particles like sand, the mix needs more water. If it hardly breaks at all, it’s too wet. But if it breaks into clumps, you’ve got the moisture just right.
3. Gradual and Even Drying Processes
Rapid drying often results in cracks, as the moisture evaporates too quickly and causes the material to shrink. To avoid this, it’s important to allow the walls to dry gradually and evenly. Covering the walls to slow down the drying process can help ensure a uniform evaporation rate, reducing the risk of cracks.
4. Control Joint Placement
Control joints are strategically placed gaps in long walls that allow for natural expansion and contraction. This prevents large cracks from forming as the wall adjusts to temperature and environmental changes. Proper placement of control joints can significantly reduce stress on the wall.
5. Proper Compaction Techniques
Thorough and consistent compaction is key to preventing cracks in rammed earth walls. If any layer is weakly compacted, it can create stress points, leading to cracks as the wall settles and dries. With a pneumatic rammer, you’re more likely to achieve consistent compaction as it’s mechanized. However, with manual ramming, it’s important to ensure that the same level of effort is applied with each strike to maintain uniform compaction throughout the mix.
How to Repair Cracks in Rammed Earth Walls
In the event that cracks do appear, it’s important to let the wall settle and reach its full extent of expansion and construction before attempting any repairs. I recommend leaving it for at least a month before addressing it. In my experience, there were times when I tried to fix cracks as soon as they appeared, only to find they reopened after a few days, causing more damage and making the wall look unsightly with repeated repairs. Rammed earth walls are living, breathing structures, so it’s essential to give them time to naturally settle before tackling any repairs.
Hairline Cracks
Hairline cracks are common in rammed earth walls and usually develop due to the natural shrinking of the material as it dries. These small cracks are typically not a cause for concern as they don’t compromise the structural integrity of the wall. I don't normally repair them if they appear as it adds to the character of the wall for me, but if a client were to insist on simple repair techniques, such as filling the cracks with a soil-based plaster or mortar, they can help restore the wall’s appearance without major intervention.
Large Vertical & Horizontal Cracks
Large vertical or horizontal cracks, on the other hand, are more problematic and require immediate attention with monitoring how it expands and contracts over time.
These cracks often occur due to improper compaction, inconsistent drying, or shifts in the foundation. To repair large cracks, the first step is to slightly widen the crack using a tool to ensure the patch will adhere properly. Next, clean the area thoroughly to remove dust and loose particles. Once the area is prepped, apply a patch mixture made from the same materials used in the original wall. Carefully fill the crack, ensuring that it bonds well with the surrounding material.
While working with earth can be complex and sometimes frustrating, especially when cracks appear, the end result is undeniably beautiful. Don’t get too caught up in the small imperfections, particularly with hairline cracks, as they often add to the natural beauty and character of rammed earth buildings. Remember these walls are living, breathing structures, and part of their charm is the way they blend with nature.
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