Building With… Rammed Earth

October 27, 2015

By Ian Cleland

Nestling into the site like it has always been there, a rammed earth building makes a statement that says it is part of its environment.

Getting started with rammed earth

Rammed earth is a material I have had experience with when constructing buildings. In fact, it all started back when I was still at school.

During the Christmas school holidays a group of friends and I were into spending all our spare time building fortifications in and around where we lived in South Tamworth, NSW.

Being a bunch of resourceful boys with access to open spaces and a plentiful supply of building materials from the scrap heaps on the many building sites around the local area, we decided to build a rammed earth structure.

We built the formwork and used earth and grass, which were in plentiful supply, to build the walls.

The next occasion was during the late 1970s, when I was part of the Mud Brick Association, and then a workshop in the early 1980s held at The Channon, a village a few kilometres from Lismore on the NSW North Coast. On all of these occasions what was constructed came about through our own efforts.

Move forward to 2013 and builders now have steel to form the walls, use mechanical equipment to assist in gathering the stocks of material needed, mixing the raw materials, filling the forms and compacting material to form the walls inside the formwork.

It is still a labour-intensive construction method but you end up with a home that is a great-looking, versatile structure.

A short history

The only place where rammed earth buildings have not been built is Antarctica. Dating back to 5000BCE, rammed earth buildings were being constructed in China and by 2000BCE the material was being used for constructing walls and foundations in China.

A great example is the earlier incarnation of the Great Wall of China, which still stands today, although in a much-weathered condition.

During the 19th century the material became popular in the USA. But with the advent of concrete, this type of construction became unfashionable, although we were left with a legacy of existing buildings dating back some 11,000 years.

Construction process

Stabilised rammed earth is made by compacting gravel, sand, silt, clay and cement between formwork in a series of layers approximately 100mm thick.

Traditional rammed earth was just that, and was often dug from the same site as the building it was destined for. But the materials for modern, stabilised rammed earth come primarily from quarries.

The modern process of making stabilised rammed earth is both labour-intensive and highly mechanical, requiring the use of powered rams.

Resurgence in earth-constructed homes in Australia has been taking place since the early 1970s, as people look for a building material that has low embodied energy and is constructed from sustainable materials.

There are now a number of licensed builders in all states of Australia who build rammed earth homes. It is also a construction method and material that an owner-builder can use.

Rammed earth advantages

Sustainable construction: There are numerous benefits to the environment in using rammed earth compared to the more modern alternatives of concrete and steel.

Low greenhouse gas emissions: Being constructed from natural materials means its carbon footprint will be low and only affected by where you source your raw materials for construction, and the stabiliser, which is generally cement.

The manufacture of cement has high CO2 production during the manufacturing process. Around 10 per cent of global CO2 emissions are from the cement industry.

Embodied energy: The inherent recyclability of rammed earth (cradle to cradle), the sources of the raw material (on-site or very local), the high thermal mass and resultant low operating costs all mean that rammed earth has a much lower embodied energy for the life of the building than comparable building materials such as brick or concrete, which cannot easily be recycled into making another building.

Thermal performance: Rammed earth acts to naturally regulate the internal temperature of a building. If a rammed earth wall is designed into the heating system of a structure, the energy required to both heat and cool the building can be greatly reduced, which further reduces the energy consumption of your home.

There is also the additional benefit of rammed earth buildings to naturally regulate the relative humidity inside the building, producing improved air quality.

This contrasts greatly with air-conditioning systems, which act to dry the air in a building and contribute to harsh working and living environments.

Structural performance: Rammed earth is very strong in compression and is very suitable for load-bearing construction. A monolithic construction also performs well under earthquake conditions, better than walls made of brick or block.

Rammed earth can be reinforced in a similar way to concrete but one has to be careful to avoid the excessive use that can cause cracking of walls.

Noise reduction: The thickness and density of the walls mean that unwanted sounds such as traffic noise are kept out.

Internal walls in rammed earth can also be extremely useful in providing sound insulation between areas with different needs — for instance between living and sleeping areas, between a public or family room and a study area, or in party walls between townhouses.

CSIRO tests indicate a sound transmission rating of more than 50 decibels for a rammed earth wall of 250mm.

Fireproof: Earth simply does not burn. This is an ideal material for bush settings and leafy suburbs. CSIRO tests showed that a 250mm rammed earth block wall achieved a four-hour fire-resistance rating.

Also, being 300mm thick and of a monolithic nature rather than of block construction, there are no vulnerable mortar joints present in rammed earth.

This can be very important in bushfire-prone areas. Having one element of a home structure fireproof also requires that in the design all other materials and construction methods also create a building envelope that is bushfire-proof.

Healthy and environmentally friendly:

Rammed earth is non-toxic, non-polluting and it ‘breathes’. Clays within rammed earth soils are hygroscopic, releasing and absorbing moisture in response to changing local atmospheric conditions.

This in turn improves air quality, removes asthma triggers and reduces respiratory diseases caused by modern materials.

Cost-effective: Unlike most types of masonry, rammed earth walls don’t need core filling or reinforcing — nor do they need plasterboard, plaster, paint or wallpaper, saving money and energy both when you build and for all the years through the life of the building.

Main considerations

Raw material selection: What will be of great importance is the suitability of the raw materials available for construction.

The material will have to be tested as part of your submission of plans and specifications to your local authority to confirm its suitability, plus what percentage of cement stabiliser will be required for structural integrity.

Connecting of building elements to rammed earth walls: Where rammed earth walls are load-bearing you will need appropriate detailing of how you will connect, for example, the roof to the walls.

This will be particularly important when considering wind loading in high-wind or cyclonic areas of Australia. You will require a suitably qualified person, such as an engineer, to provide and certify suitable details. This will also include the lintels of doors and windows.

Protecting rammed earth walls from excessive rain:

Like mud brick, it is important to protect the walls from long-term exposure to rain and wetting at the base of walls, to minimise erosion of the wall.

Again, what is important here is to design the structure with suitable eave overhangs to lower exposure and not have areas in your design with low areas where rainwater can pond against the walls.

Reducing dusting from walls: Over time, rammed earth walls will produce dust.

This is important on the interior side of the walls, so a clear sealing coat can be applied that maintains the walls’ natural appearance while it controls dusting.

Natural beauty

Like all natural building materials it is all about creating an aesthetic that connects your home back to the earth.

Rammed earth is such a natural wall structure system that allows you to create natural beauty that is hard to surpass with other man-made materials.

It will make you a home that will have an ageless quality. If you are fortunate enough to also combine this with other naturally available materials, such as stone and timber, you will create a home that will last for centuries.

Everybody deserves the right to experience great design, and rammed earth is a material that can help deliver that. Be bold and with professional help, be part of the process of creating your dream rammed earth home.

By Ian Cleland

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