An adobe block is an unfired block of loam, usually mixed with sand and often with straw or another fibre, formed in a mould and then dried in air and sun. The Spanish word adobe — from the Arabic al-ṭūb, ‘the brick’ — is the internationally used name for what in earth building is simply called an earth block or mud brick.
The difference from a fired brick is fundamental: a brick is fired in a kiln and thereby becomes irreversibly ceramic and frost resistant. An adobe block is only dried. It therefore stays sensitive to water, but at the end of its life it can also be returned entirely to loam.
Manufacture and composition
- Loam with a balanced clay content; too rich and it cracks while drying, too lean and it will not bind.
- Sand to limit shrinkage.
- Straw, hemp or wood fibre to counter cracking and reduce weight.
- Forming and drying: by hand in timber moulds or machine-pressed. Drying takes weeks and happens out of direct sun and rain, because drying too fast causes cracks.
Germany has a set of standards for factory-produced earth building materials — DIN 18945 for earth blocks, DIN 18946 for earth masonry mortar and DIN 18947 for earth plaster mortar — issued in their second generation in 2018. These are frequently referenced elsewhere in Europe where no national product standard exists.
Properties
- Heavy and thermally massive. An internal wall of earth blocks adds mass to a lightweight timber-frame house and damps down temperature swings — exactly where such a house is weakest.
- Moisture buffering. Earth blocks absorb and release water vapour, keeping indoor humidity more stable.
- Good sound insulation because of the weight.
- Non-combustible.
- Low compressive strength compared with fired brick or calcium silicate block. Load-bearing earth masonry is possible but calls for calculation and a standardised product; for a non-load-bearing internal wall this is not an issue.
- Not water or frost resistant. External use always needs protection.
Using them in practice
- Non-load-bearing internal walls, by far the most common application in Western Europe.
- A lining wall as a thermal buffer behind a south-facing window or behind a wood stove.
- Infill panels in timber-frame restoration, where the earth block matches what was originally there.
- Laid in earth mortar, not cement mortar: only then does the wall stay demountable and reusable, and the whole behaves as one material.
Points to watch
- A good hat and good boots. Generous roof overhang, a water-resistant plinth and a sound damp-proof course; earth must never stand in rising damp or splash water.
- No cement-based finish over it. Cement render seals the wall so moisture is trapped in the earth. Finish with clay plaster or lime plaster.
- Avoid wet rooms, unless the splash zone is fully protected by tiling on a suitable backing board.
- Allow for the weight. Earth block walls are heavy; check the load capacity of the floor, especially a timber upper floor.
- Fixings. Do not simply hang heavy cupboards on an earth wall; use through-fixings or timber blocks built into the wall.
Related terms
- Loam
- Clay plaster
- Clay
- Claystone
- Bonding pattern
- Sustainable building
- Circular economy
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