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Earth and Construction

By: Jennifer Gray - Updated: 26 Jan 2018 | comments*Discuss
Earth Construction Earth Building Cob

Earth construction is the practice of building with unfired, untreated, raw earth. It has been successfully used around the world for over 11,000 years, and it is estimated that around half the world's population today live and work in earth buildings.

Types of Earth Building

The techniques and methods for earth construction vary with culture, climate and resources, but within the sustainable building movement they can be categorised as: cob, rammed earth, wattle-and-daub, light straw, earthbags, earth bricks, earthen floors, and earth plasters and finishes.

Cob Building
The word cob means "lump or rounded mass". Cobs are made from moist subsoil mixed with sand and unchopped straw, and kneaded into stiff mud loaves that are then rammed together by hand to form a self-designed structure. The soil mixture should be approximately 1 to 2 parts clay (binder) to 1 part silt, 2 to 3 parts sand, and 3 to 4 parts gravel, and there should be around 3% straw to act as a strengthening binder and to prevent cracking.

Cob dries almost as hard as concrete and can be used for self-supporting, load-bearing walls. Thick walls are built (up to 6 feet wide) by working in layers, letting each one harden before adding the next layer. The wall is then plastered with clay or lime plasters, or left unfinished, but in wet climates an overhang or shelter might be necessary to protect an unfinished wall.

Building with cob is simple, cheap and requires few tools other than hands and imagination. It can be time-consuming, but there are many advantages to cob including its extreme durability, strength, fire-resistance, insulation properties and the ease with which it can be aesthetically shaped and sculpted.

Rammed Earth
Moist subsoil is layered into a temporary formwork (shuttering) and then rammed (tamped) for compaction by manual or mechanical means. The layers can be rammed continually until the wall is complete, with no need to wait for each layer to dry out. The walls are then allowed to dry naturally once the frame is removed. Rammed earth is stronger than cob, but more expensive because of the shuttering required.

Light Earth or Straw Clay
A combination of cob and rammed earth, this involves coating loose straw or other fibrous material with a clay slip that is rammed tightly in layers into a timber frame. It is lighter than cob and has a higher insulation value, but is not as strong and must only be used as an infill with the timber frame. The walls are allowed to dry before final plastering takes place. Light earth has also been used between rafters as roof insulation, and as insulation underneath earthen floors.

Wattle-and-Daub - One of the oldest earth techniques, this involves weaving thin branches together (wattle) as a support for mud plaster (daub). It does not have the super-insulation properties of straw-bale or clay-straw, but provides good thermal mass.

These are soil-filled sacks that can be used to create walls and dome structures. This technique is still being explored, but seems to offer a quick and easy method for natural building, and may be especially suitable for temporary or disaster relief housing. Moist soil is put into a burlap sack or plastic bag, stacked into place on a wall, and then compressed using a simple hand tool. Earthbags are increasingly being used as foundations for cob and straw bale houses.

Earth Bricks
These are made from an earth and straw mix, similar to cob, placed into moulds to form bricks or blocks, and then dried out in the sun. The most popular type is adobe brick. Normal bricklaying techniques are used, using an earth or lime mortar. Earth bricks have load-bearing structural properties but provide poor insulation.

Earthen Floors
This involves pouring one or more layers of an earth mixture over a substrate of gravel, pumice or sand. The site needs to be carefully prepared first to ensure drainage and low moisture. Hardening agents are sometimes added such as blood, manure or lime. When the floor is completely dry, it is sealed with successive applications of linseed oil and turpentine, and waxed for protection.

Earth Plasters and Finishes
These are made from clay slips or lime and are becoming increasingly popular. They are non-toxic, and allow walls to breathe, so that any moisture trapped inside the walls can evaporate out.

Building with Earth, For the Earth

Earth is one of the most abundant, basic building materials. It is low technology, easily worked with simple tools, and yet can be used by anyone to construct walls, floors and roofs of advanced architectural design. Earth buildings are highly durable, have good humidity regulation and sound insulation, and are non-toxic, non-allergenic and fireproof. They provide excellent thermal mass and insulation when built with thick walls, and when used with passive solar design. Earth buildings have very low embodied energy, and low environmental impact, especially when the material is sourced on site. As a building material and methodology, earth is the ultimate sustainable solution.

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Rowland Keable - Earthen Architecture guru will be at Brighton Permaculture Trust's Green Architecture Day on 10 March 2018, to talk about big builds in earth & chalk. Please see our website for details: brightonpermaculture.org.uk/courses/greenarchitecture
BPT - 26-Jan-18 @ 3:13 PM
I wonder if super adobe building would be considered at all... as in would it be worth or a silly dream to apply for planning permission for a super adobe house?
rafaelr - 28-Sep-16 @ 11:40 PM
Shelly123 - Your Question:
We are a family of five no small children we've been saving up for a few years now trying to get out of this fast rat race of a life, we are looking for a piece of land to buy from a farmer or anybody whom has land we want to live in a mud house be self efficient if anybody has information on which I can buy land please please get in touch I live in England uk thank you

Our Response:
Unfrotunately land for residential use is scarce and expensive (because developers are have a keen interest in any available). However, we hope someone sees this and can offer you something :-)
SustainableBuild - 22-Oct-15 @ 10:46 AM
We are a family of five no small children we've been saving up for a few years now trying to get out of this fast rat race of a life, we are looking for a piece of land to buy from a farmer or anybody whom has land we want to live in a mud house be self efficient if anybody has information on which I can buy land please please get in touch I live in England uk thank you
Shelly123 - 21-Oct-15 @ 12:11 AM
i would like to know is it cheaper to build a cob house or a hearthship of the same size?
gigilondon - 4-Oct-15 @ 7:24 PM
A garage across the road from me is working in a lage tin builtt shed.They are maintaining tractors oil changing etc.They do not have a concrete floor just earth. So al petrol oil and other chemicals are going directly into the soil is this legal orshould they have a concrete floor. ,
cluff - 7-Jul-15 @ 6:26 PM
@Anna. Hope you get some good responses. We've also posted this on our sustainable build facebook page to see what responses we get.
SustainableBuild - 26-Jan-15 @ 10:52 AM
Hi... Daydreaming for "my" strawbale home that I want eventually to be able to afford and build (post and beam, not loadbearing)... Thinking about earthen /rammed earth floors over radiant heating: wondering how best to achieve strength (so that not damaged by heavy furniture) and enhancing/choosing/changing colours of the top clay slips - anyone with experience/advice?
Anna - 22-Jan-15 @ 12:15 PM
"Thick walls are built (up to 6 feet wide) by working in layers, letting each one harden before adding the next layer. " This is completely incorrect. Cob walls are generally around 24" - 36" thick. I suppose you could build them as thick as 6', if you where planning on parking several pieces of heavy construction equipment or driving over it with loaded tractor trailers. Otherwise this would simply be massive overkill!!
deaconblue9038 - 15-Feb-13 @ 2:41 AM
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