Rammed earth

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Image:Rammed earth wall - Eden Project.jpg

Rammed earth construction, also known as pisé de terre or simply pisé, is an age-old building method that has seen a revival in recent years as people seek low-impact building materials and natural building methods. Traditionally, rammed earth buildings are common in arid regions where wood is in scarce supply.

Walls are constructed from a mixture of earth that has suitable proportions of sand, gravel and clay sometimes with an added stabilizer. Traditional stabilizers such as lime or animal blood were used to stabilise the material, but cement has been the stabilizer of choice for modern times.

Formwork is set up creating the desired shape of the section of wall, damp material is poured in to a depth of between 100 to 250mm (4 to 10 inches). A pneumatically powered backfill tamper - something like a hand-held pogo stick with a flat plate on the bottom - is then used to compact the material to around 50% of its original height. Further layers of material are added and the process is repeated until the wall has reached the desired height. The wall is so solid that if desired the forms can be removed immediately. This is necessary if wire brushing to reveal texture is desired otherwise walls become too hard to brush after around 60 minutes. Walls take some time to dry out completely, but this does not prevent further work on the project. Any exposed walls should be sealed to prevent water damage - there are several proprietary products specifically designed to seal earth walls.

In modern variations of the method the rammed earth walls are constructed on top of conventional footings or a reinforced concrete base, sometimes with extra ground insulation from a horizontal layer of styrofoam. Some builders also add coloured oxides or other items such as bottles or pieces of timber to add variety to the structure.

Once completely cured the walls are very workable. It is easy to drive a nail or screw into them and they can be patched if necessary with the result being undetectable if the same material was used.

One of the significant benefits of rammed earth constructions is its excellent thermal mass; it heats up slowly during the day and releases its heat during the evening. This can even out daily temperature variations and reduce the need for air conditioning and heating. On the other hand, rammed earth is not a good insulator. Like brick and concrete (which also have excellent thermal mass), rammed earth is often insulated in colder climates. The thickness and density of the walls lends itself naturally to soundproofing and the materials used in the walls make them virtually fireproof.

Prior to the use of cement as a stabilizer, rammed earth buildings were most successful in dry climates with limited availability of building materials other than earth. Rammed earth has become a viable material in wetter climates, either through the use of cement stabilisation, through placing the earth walls within the weatherproof fabric of the building, or by the application of external insulation and weatherproofing.

[edit] See also

[edit] References

Western Living "earth to saltspring", October 2003.

[edit] External links

The Natural Building Network - find natural builders, teachers and resources.
Earth Architecture - A website whose focus is contemporary issues in earth architecture.
Rammed Earth - The Australian Connection - A good description by an owner-builder can be found at this Australian Rammed Earth site. Also has many photos and links.
Rammed Earth in Canada - A good overall rammed earth site.
Historic Rammed Earth - A good site about the history of rammed earth throughout the world, and research into preservation techniques.
Stabilized and Insulated Rammed Earth - The first rammed earth builder to build insulated rammed earth buildings that are earthquake engineered.
Simmonds Mills - A UK architecture and building company using unstabilised rammed earth construction
Rammed Earth Works Website for the company owned by David Easton a noted expert in rammed earth and PISE who has built many homes and buildings and also written several books on the subject.