HOW TO MAKE STABILISED SOIL BLOCKS
Earth or soil has been used to make buildings all over the world for thousands of years. Many
earth buildings have stood for hundreds of years. The main enemy of earth buildings is water.
Both rain and rising groundwater or moisture can damage earth structures.
Here we are dealing with making stabilised soil blocks. The making of these blocks deals with
the two main problems that can happen with earth buildings:
Stabilisation: Adding something to the earth that helps to make it more resistant to
attack by water, something that helps "waterproof" the earth. Stabilisation can also
increase strength.
Compaction: Pressing the earth makes it stronger in "compression", that is it allows
earth walls to take more weight on them without collapsing. Making earth into blocks
is also a way to make stabilised earth into a form that can more easily be used by
builders.
These notes are to help anyone who wants to make SSB's. The notes concentrate on
stabilising soil with cement and building lime is mentioned as an alternative for some soils.
The most common type of cement available is Ordinary Portland Cement (OPC). If lime is
used as a stabiliser, it should be hydrated lime building lime. Hydrated lime is made by
burning limestone in a very hot fire (900°C). Burning produces quick lime. An exact amount
of water is then added to produce hydrated lime. The lumps formed are then ground to a
powder for easy use.
The notes cover all the stages in the making of SSB's that is:
1. Soil testing - choosing which stabiliser & how much to use.
2. Soil preparation - crushing, sieving and mixing.
3. Block pressing - correct wetness and amount to put in press.
4. Block curing - how to keep the blocks after pressing.
5. Block testing - tests to do yourself and others that can be done.
SOIL TESTING
There are two groups of tests worth doing. Group 1 will help you to get a feel for the soil, but
not tell you if it is a good one for stabilisation unless you are very experienced. Group 2 are two
simple tests that will tell you enough about the soil to see if it is okay for making SSB's, how
much and which stabiliser to use.
To use cement as a stabiliser you are probably looking for a soil which is less than 1/5 (20%)
silt and clay. In other words, you want a sandy soil which preferably has a good mixture of
particle sizes from medium gravel (about 6mm - millimetres - diameter) to fine sand (0.06mm
diameter). Soils with higher clay contents can be stabilised but need more cement, or hydrated
lime can be used.
Technical Advice Notes Number 1, "How To Find A Good Soil For Making Burnt Bricks", will
tell you how to get a soil sample for testing.
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