What is CSEB? A guide to compressed stabilised earth blocks

Compressed stabilised earth blocks, or CSEB, are building blocks made from local soil mixed with a small amount of stabiliser, usually cement, and compressed in a machine. They are not fired. Because the main ingredient is soil from on or near the site, they can cut both material and transport costs.

How CSEB are made

1. Soil preparation. The soil is dried, crushed and screened to remove stones, roots and lumps.
2. Mixing. The soil is mixed with the stabiliser, then with just enough water to make a damp, crumbly mix.
3. Compression. A manual or hydraulic press compacts the mix in a mould into a dense block.
4. Curing. Blocks are stacked under cover and kept moist while the stabiliser hardens, usually for several weeks before use.

On an automatic line, crushing, screening and batching are done by machine before the press. The how it works page shows that sequence.

Which soils work

Not every soil makes good blocks. It needs enough sand for strength and enough clay to bind it together.

• Too much clay and blocks shrink and crack as they dry.
• Too much sand and blocks are crumbly and weak.
• Organic matter, such as topsoil with roots, weakens the block and should be left out.

A simple field check, shaking soil and water in a glass jar and watching how much settles as sand versus silt and clay, gives a first idea. For a production plant, have the soil tested and make trial blocks before you buy a machine. Sand can be added to a soil that is too clayey.

The stabiliser

Cement is the most common stabiliser and suits sandier soils. Lime suits soils with more clay. The dose is small compared with concrete, and the right amount is found by testing trial blocks made from your soil. The Indian Standard for stabilised soil blocks is IS 1725.

Where CSEB fits in a building

• Load-bearing and partition walls in homes, schools and low-rise buildings, designed by an engineer.
• Interlocking versions that need little or no mortar. See interlocking blocks and mortarless construction.
• Hollow interlocking blocks that take vertical reinforcement and grout through their holes.

Like any earth building, CSEB walls last longest with good detailing: a raised plinth that keeps the wall clear of splashing water, and roof overhangs that keep driving rain off.

Benefits and limits

• Uses local soil and needs no kiln.
• Uniform blocks from a steel mould, so walls go up faster.
• A natural earth finish that many owners leave exposed.
• Quality depends on the soil and on curing, so testing matters more than with factory-made materials.

CSEB machines from Possible Machines

We build CSEB and interlocking block machines, from semi-automatic presses to lines with automatic soil processing and batching. Describe your soil and the block you want, and we will advise on the machine and moulds.