Living in a time where new highly engineered materials are developed nearly every day, the idea of going back to compacted earth may seem a little primitive. But, just because we were using it thousands of years ago doesn’t mean it’s not a great choice today - with a few improvements, of course.
WHAT IS IT?
More of a construction technique, rammed earth involves compacting a mix of raw materials to create a solid structure. The types of materials and their ratios will vary depending on the structure’s purpose and the desired colour and texture, but may include earth, sand, clay and gravel. If extra reinforcement is needed, cement will be added to create stabilised rammed earth.
WHAT WE LIKE ABOUT IT
If the rammed earth technique has stuck around all these years, there must be a few good things about it, right?
Made up of raw materials, rammed earth can be very sustainable if recycled and locally sourced. It also has a high thermal mass and can help stabilise temperatures within a home without the need for electric heating and cooling. Then there’s the versatility. Whether you want angles or curves for a feature wall, or it needs the structural capability for loadbearing walls in a multistorey design, your rammed earth mixture can be adjusted accordingly – and there’s no need for framing, cladding or paint. Depending on the composition of your mixture, it can also come in a wide variety of colours and textures.
It’s also very durable with the potential for high structural capabilities if mixed with cement. Particularly of note in Australia, it has no flammable components and can resist fire for up to four hours. As for moisture resistance, it performs well (especially with water-repellent additives) and can be exposed to the elements, although water protection is still recommended at the tops and bottoms of structures. And to make it even better, in the right conditions it can even last centuries with little-to-no maintenance.
THE NOT SO GOOD
While the above all sounds excellent, there are certainly reasons why rammed earth might not be a good choice for your home.
First, it’s important to consider your location. Structural walls built with rammed earth must be a minimum of 300mm thick and can take up a lot of precious space if you’re on a tight block. It also has minimal insulating properties and may degrade with continued exposure to moisture, so always consult with an expert to make sure it’s suitable in your local climate. Limited suppliers around Australia can also make it difficult to source and may lead to increased costs and carbon emissions from transportation.
Thick walls are necessary for structural stability.
The finished product being a solid structure can also create some significant challenges. Services must be pre-laid, and accurate forward planning (best done by an experienced builder) will be needed to avoid frustrations down the line. If damage occurs or changes are needed, they can be very difficult and costly to implement. On top of this, it’s virtually impossible to replicate your aggregate mix, so while minor damage can be patched up relatively easily, hiding the repair job will be much more difficult.
BUILDING PROCESS
Compressing earth may seem like a simple process but, in reality, it’s lengthy and labour intensive. The exact process may vary slightly depending on the shape of your structure so, for simplicity, let’s look at how we’d build a wall. The most important point to note is that rammed earth needs to be built in layers of approximately 600mm high and panels a few metres long. So, what’s the process for each of these layers?
1. Formwork: The first step is to build the formwork which will act as a mould for the rammed earth to dry into shape. The sides should be built to full height, while the surface formwork should be installed in stages to allow easy access when ramming the mixture. Dimensions should be carefully engineered by the architect, and all services carefully pre-laid.
The services are included in the formwork so they’re in place when the mixture dries.
2. Mix the base: Next, it’s time to make your rammed earth mixture by combining earth, sand, clay and/or other materials with water. This can be done on site and may even use soil or other materials found on the property.
3. Load it in: Now that you have the formwork and the base, it’s time for your rammed earth structure to start truly taking shape. The aggregate mix can be loaded into the formwork and compacted or ‘rammed’, either manually or with a machine (at Arklen we use a hydraulic rammer). Once your first layer is sufficiently compacted, you can move on to the next layer, and so on until the panel is complete – and then you can move on to the next panel.
4. The final product: Once all layers have been sufficiently compacted, it should be left to rest overnight before the formwork can be removed and the final panel revealed.
Finished panels next to formwork for the next panel. Note the horizontal lines which mark the different layers during compaction.
HAUSEN COURT, BANJUP
Our most extensive rammed earth project was Hausen Court in Banjup, and we think it looks stunning:
On a large site, the rammed earth helps give the home visual weight, firmly anchoring it in place.
Rammed earth walls at the front gate offer a hint of what will be found in the home.
TRADE SECRETS
Rammed earth is a unique material that can be quite challenging to work with, so we’d like to finish off this blog with some trade secrets we’ve learnt from working with it. If you have any other questions, need advice or might be keen to start a rammed earth project with Arklen, feel free to get in touch.
Imperfections and undulations are one of the appealing features of rammed earth, but these can make joins against straight-edged fixings difficult to execute. Silicone can be used to fill in any gaps, but also consider timber trims, window casings and other creative solutions to hide the rough edges.
To future-proof the home and allow for changes to the services built within the walls, we usually run extra sleeves/conduits that are ready to be used if needed.
Your options for the finish texture aren’t just limited to varying degrees of smoothness. By adding a pattern to your formwork it’s also possible to imprint that pattern into the rammed earth. This could be anything from a fern leaf pattern to your house number.
You can make samples to see how your mixture looks when dry – and we highly recommend doing so.
