The soil is then passed through a sieve or screen. The sieve should have a mesh size of 5 or
6mm. All stones bigger than this should be put aside as they will cause cracking if they get
into a block.
If your soil has too much clay, you might mix it with sand to get the right proportions for
stabilising.
Once the soil is crushed and sieved it will need to be mixed with the stabiliser. Mixing should
be done with the soil and the stabiliser both dry. It is probably easiest to measure quantities
by volume (although weight would be more exact).
Perhaps, when you know exactly how much stabiliser to soil you need, you might make a
gauge box as shown. A wheelbarrow or buckets will do just as well to measure volumes.
Mix the soil and stabiliser together very well. The best way to tell when you have done
enough mixing is when the mix is all the same colour.
Mix in the amount of water that is needed slowly a little at a time. Sprinkle the water over
the top of the mix with a watering can. Mix well, turning the mix over several times.
The mix is wet enough when a handful dropped from shoulder height just breaks up when it
hits the ground (The Drop Test). You should not be able to squeeze water out of a handful of
the mix.
If you are using cement the mixture should be pressed straight away. With lime the mix
should be allowed to stand for a short time and then turned again before pressing.
Hand mixing with shovels is often the most efficient, satisfactory and cheap method. A
concrete mixer is not suitable for mixing soil because the soil will stick badly inside the
drum.
DROP TEST - no equipment required - medium accuracy.
Method:
Take some soil that has had some water added to
it. Squeeze the damp soil into a ball in your hand.
Then with your arm straight out at shoulder level,
drop the soil ball onto a smooth clean surface at
ground level and observe the result:
if the soil stays in one piece it is too dry; add
water and try again;
if the soil is still in one piece the clay content is
too high;
if the soil breaks into many pieces, it is too wet;
leave it to dry a while and try again;
when the dropped ball breaks into only a few pieces it is close to the optimum water
content, and suitable for use.
Continue to use the drop test to check the water content of the soil as it is being used.
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