Whether you’re a homeowner looking to DIY rammed earth or a contractor wanting to add rammed earth to your repertoire, the first things you’ll need are confidence and know-how. While skills in carpentry and concrete are helpful, a lot of research and trial-and-error go into building rammed earth properly for the first time.
Finding the Right Mix
Not all rammed earth mixes are made equal. Whether you’re working with quarry mixes or local soil, finding the right mixture ratio is essential for the success of each build. For example, clay soils may require more sand while soft soils need an aggregate. Most modern rammed earth structures are stabilized with a small percentage of admixtures, such as 6-10% portland cement.
Another factor to consider for the earth mixture is waterproofing. Waterproofing during the mixing process is best done by adding Tech-Dry® Plasticure to the soil mixture. Plasticure is a water-based silicone admixture formulated specifically to waterproof rammed earth throughout and for its lifetime. By adding Plasticure in the mix, you avoid costly maintenance down the road. Aussie Built projects aren’t constructed without it.
A contractor should experiment with the rammed earth mix and perform small-scale tests to determine the durability, strength and color of the mixture. Aside from testing samples yourself, you’ll want to take your test samples and rammed earth mix to your local geotechnical lab to get tested for compressive strength and sieve analysis. For structural integrity and peace of mind, every builder should have their samples tested.
Preparing the Forms
Once you’ve poured footing and stem walls, developed the right mix, prepared a stockpile of rammed earth mix, allocated all equipment, machinery and tools for the job it’s time to plan the forms. A large percentage of the work on rammed earth structures is preparing and setting up the form system. It is a major component of the building process, in both time and importance. The form system details the rammed earth wall and aligns the structure square, plumb and level. The forms provide shape and structural strength during ramming. Detailed planning is necessary for even small projects. Form systems materials vary based on factors such as size of structure, complexity, and whether the forms will be reused for future projects.
Concrete footings and stem walls need to be built to meet engineering approval before diving into the rammed earth process.
Ramming the Earth Mix
Once forms are set on structural footings and the earth mixture is prepared, it’s time to start ramming. For the most part, ramming is done using pneumatic rammers for efficiency and ease. Manual hand rammers are used in corners, tight spaces and around electrical boxes or plumbing pipes. With 5- to 7-inch layers of moistened rammed earth mix, including Portland cement stablizer and Plasticure, placed in the form, workers tamp each lift line into a compact and solid layer about ⅔ of its original volume.
The forms are filled and compacted to their intended height. Rebar is installed per engineered specifications. A concrete bond beam, generally preferred, is then poured on top of the rammed earth wall for strength and to allow for mechanical fixings and tie plate to be installed, also allowing for roofing and additional framework.
Maintaining Rammed Earth
While rammed earth has proven its ability to stand the test of time, minimal maintenance is required to keep your home or structures standing tall. We at Aussie Built incorporate Plasticure in all our projects to ensure waterproofing for the lifetime of each build. In addition to Plasticure, we recommend Tech Dry’s acrylic-based Earth Binder to be used on interior and exterior walls to bind all dust and crumbling walls, leaving a smooth, breathable, desired surface finish. After Earth Binder, Tech-Dry’s Stabilised Earth Water Repellent W is applied to the exterior walls only after construction to provide outer wall protection and to prevent staining and weather damage.
When Plasticure is not added in the mixture for waterproofing, both Earth Binder and Stabilised Earth Water Repellent are required on a regular maintenance schedule, depending on weathering, generally every 3-5 years.
Before you begin, it’s important to consider starting small. Practicing on a shed or entry gate to get a feel for rammed earth can prevent costly mistakes later. Make sure your mixture is effective and has the strength to stand tall before diving into a larger project.
The Cost of Rammed Earth
For homeowners wanting to experiment with rammed earth in their own build, we recommend having an experienced professional on-site to get things started. There’s a huge difference between researching the process and being hands-on for the first time. Having a seasoned builder that can answer questions and pass on their tricks of the trade will save you time and money. The value of paying a little extra upfront for the professional help and use of their equipment far exceeds the cost of mistakes and mishaps.
Between form systems, materials and machinery, the price tag for a rammed earth setup can add up. However, form systems and equipment are reusable and one-time expenses. Adding this technique to your skillset offers a unique opportunity to be one of few in a growing industry.
As a professional contractor trying to break into the rammed earth industry, it’s important to have a grasp on the process before adding all this equipment to your lineup. The more you or your crew work with rammed earth, the more systemized you’ll work and less money you’ll spend on time, training and labor. Getting started with rammed earth can be intimidating, but having an experienced rammed earth mentor on-call makes all the difference.
Training and Consulting
If you’re trying to learn more about rammed earth from an expert in the field, you won’t find a better guide than Aussie Built founder, builder and carpenter Mick Gower. Mick studied construction in Australia and has traveled the world to learn different building techniques. With over 35 years of working on the tools and extensive build experience, sustainable building and rammed earth have become a passion. He's developed a vast amount of knowledge and know-how over the years surrounding the style. From general contracting, consulting and building rammed earth structures from the ground up to running the exclusive U.S. supplier of rammed earth products for construction and maintenance, Aussie Built can help make your project a success.