Adobe versus Cob verses Mud Brick: What’s the Difference?

What do adobe, cob and mud brick have in common?

Adobe, cob and mud brick are among the oldest building methods in the world. All three use a natural mix of earth, clay, sand and water, often with organic fibres such as straw. The clay binds the mix, the sand gives it body, and the fibres help resist cracking as it dries.

Earth buildings are valued for their low embodied energy, local materials and thermal mass. Where they differ is in how the earth is shaped and built into walls.

What is adobe?

Adobe is earth formed into bricks, usually in timber moulds, then left to dry in the sun. Once cured, the bricks are laid in courses with a mud mortar, much like conventional brickwork.

The word came into English from Spanish, which took it from the Arabic al-ṭūb (“the brick”), a word that traces back to ancient Egyptian. Adobe is strongly associated with the American Southwest, Latin America, North Africa and the Middle East. Because the bricks dry before they are laid, walls can go up relatively quickly once enough bricks are made.

Is mud brick the same as adobe?

Essentially, yes. “Mud brick” is the common Australian term for sun-dried earth bricks made and laid in much the same way as adobe.

Mud brick has a strong local history. Eltham, on Melbourne’s outskirts, is known for its mid-century mud brick homes, and the method remains popular with owner-builders. The movement is closely tied to Alistair Knox (1912–1986), a largely self-taught designer and builder who is acknowledged as the founder of Eltham’s mud brick building movement. Over a career spanning 1946 to 1986, Knox designed more than 1,000 buildings, many of them in mud brick, and in 1984 he received an honorary doctorate in architecture from the University of Melbourne.

Many modern mud bricks follow the traditional recipe, while some include a small amount of stabiliser to improve durability.

Can you build with mud brick in Australia?

Yes, but it takes more planning than conventional construction. The National Construction Code has no Deemed-to-Satisfy provisions for earth walls, so mud brick is usually approved as a Performance Solution. A structural engineer provides the design and supporting evidence, and the building surveyor or certifier assesses and approves it. Standards Australia’s HB 195: The Australian Earth Building Handbook is the main reference for earth wall design and testing.

Earth walls offer good bushfire performance and excellent thermal mass for moderating indoor temperatures. However, they have low insulation values (R-values), so external walls usually need added insulation to meet current energy efficiency requirements. A successful mud brick build also depends on robust damp-proofing, generous roof eaves, and professionals who understand the approval process for earth construction. Requirements vary, so check with the local building authority.

What is cob?

Cob is built wet. Instead of forming bricks, builders mix earth, clay, sand, water and plenty of straw into a stiff dough, then build walls up by hand in layers. Each layer is trodden and pressed into the one below and allowed to firm up before the next is added.

The result is a monolithic wall with no joints. Cob is closely linked to the West Country of England, particularly Devon, where many centuries-old cob houses are still lived in. Because it is shaped by hand, cob suits curves, niches and sculptural forms that bricks can’t easily achieve.

How is earth building regulated in Australasia?

New Zealand has dedicated earth building standards (NZS 4297, NZS 4298 and NZS 4299) that cover cob alongside adobe, rammed earth and pressed earth brick, with reinforcement requirements to suit the country’s seismic conditions. The standards were revised in 2024, though industry groups are still pushing for those latest editions to be cited as Acceptable Solutions under the Building Code.

Australia has no dedicated earth building standard. Cob, like mud brick, generally goes through a case-by-case Performance Solution. Because cob has less established Australian testing data than mud brick, approval can involve additional engineering input and testing, and wall designs must still meet energy efficiency requirements.

How do adobe, cob and mud brick compare?

What do earth walls need to last?

All three share one weakness: unprotected earth softens and erodes when it stays wet. Earth builders often say a wall needs “a good hat and good boots”, meaning wide eaves to shed rain and a raised footing with a damp course to keep the base dry.

Earth walls also need to breathe. Dense cement renders and non-breathable coatings can trap moisture inside the wall, a common cause of blistering, salt damage and coating failure. Protective treatments should repel liquid water while letting water vapour escape.

Protect your earth building with Tech-Dry

Tech-Dry manufactures a range of protection products for earth construction. These include Mud Brick Water Repellent and Earthshield, solvent-based water repellent sealers for mud brick; Earth Binder and Earth Bonding Emulsion, dust-binding sealers for internal earth wall surfaces; and Earthaid, an admixture for producing water-resistant earth renders and paints.

Talk to the Tech-Dry team about the right treatment for your earth building, or explore the earth building protection range.