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WHAT IS IT?
Natural high-clay earth is extracted from grounds usually local to the manufacturing site. The clayey earth is then mixed with straw, water, and aggregates like sand and is cast into open moulds on the ground, and are left to be sun-dried. Cob/Adobe bricks are never kiln-fired.¹
Walls are created by laying bricks using earth mortar, and then smoothened out before drying. Cob bricks (like the sample provided) can also be used to repair existing Cob houses.
Cob is traditionally not in brick form. Cob is usually moulded in place, wet like clay, to form organic walls and other building elements, and left to sun-dry as a monolithic piece.
MATERIAL LIFE CYCLE
KEY INFORMATION:
This material is manufactured and available in the UK.
At least 250mm wall thickness for load-bearing walls.²
Usually a maximum of 2 stories due to its low structural strength (3.2 Tonnes Compression Strength).
This material can be known as 'Cob', 'Cob Bricks', 'Adobe', 'Adobe Bricks' and 'Mud Bricks', with some differences between them.
Naturally fireproof.
Sound insulating.
Cob/Adobe bricks experience a 4% shrinkage when dried. Building with bricks instead of Cob monolithic walls ensures structural integrity and no cracking after walls are set.³
Has a high thermal mass but poor insulation.⁴
Is very weather resistant but requires sufficient roofing and foundations to protect from weather and dampness.⁵
A great material choice for self-builds as material is easy to work with.
A cob monolithic wall is more seismic resistant than bricks due to its uninterrupted build up.
*If material is available to be extracted from construction site itself, the above pricing figures are irrelevant, however it is important to consider increased labour costs and time consumption.
Challenges with using Cob / Adobe Bricks⁶
Challenges with using Cob / Adobe Bricks⁶
Built Examples using Cob / Adobe Bricks
Sample provided by earthblocks.co.uk
Sources:
¹ https://www.solidearth.co.nz/earthbuilding-information/building-with-adobe-brick-technique/
² https://sustainablebuild.co.uk/cobbuilding/
³ https://drive.google.com/file/d/1AHLCPmnoUrKCb7E50FU4YgEpSA7wHd-c/view?usp=sharing
⁴ https://earthblocks.co.uk/2022/11/28/cob-blocks-thermal-qualities/
Insulating Cob/adobe walls: https://buildingrenewable.com/cob-house-insulation-how-home-warm-winter/
Further Reading:
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