GROUP 1
(a) TOUCH TEST: Take some dry soil that is not in lumps and feel it between your thumb
and fingers. If it is very gritty and sharp this means that there is a lot of sand. If it is smooth
and powdery (like white flour or talcum powder) then there is a lot of clay and silt. Make a
note of the colour of the soil, any lumps, stones or different coloured deposits.
(b) SCRATCH & POLISH TEST: If possible, take a small lump of the soil and scratch it with
your thumb nail. If it is a fine soft powder that comes off then the soil is high in clay. If the
lump crumbles easily and gritty pieces come off, this means high sand.
Now try to polish the lump with the back of your thumbnail. It may help if you wet your nail
a little. If you can polish the surface to a nice shine this means that there is a lot of clay in
the soil.
(c) TONGUE TEST: If you put your tongue onto the surface of the lump that you have
smoothed, you might notice that it sticks. The more your tongue sticks the more clay there is
in the soil. Remember you want a soil with only a little clay for making a strong and cheap
SSB with OPC.
(d) ROLLING TEST: Take a little of the powdered soil in the palm of one hand. Wet it a little
so that it sticks together. If it sticks together well, and you can shape it and roll it into a thin
thread then there is clay in the soil.
Take your wetted soil and try to roll a thread on some flat clean surface. If you can roll a
thread less than 3 millimetres in diameter, then there is probably too much clay in the soil
to make stabilised blocks well and cheaply.
(e) DROP TEST: Take a wetted lump of the soil and mould it in your hands, the soil should
not be so wet that water can be squeezed out. Drop a lump that just fits into your one hand
onto a hard surface from shoulder height. If the lump stays in one piece, there is probably a
lot of clay in the soil. If, on the other hand, the lump breaks up into a few smaller pieces
there is probably quite a lot of sand.
GROUP 2
(a) SEDIMENTATION JAR TEST: Pass some of the soil through a sieve with 5 or 6 millimetre
mesh (an ordinary kitchen strainer is usually okay). Take a straight sided clear glass jar and
fill it one-third full with the sieved soil. Add water until the jar is % or % full. Shake the well
for one or two minutes. Place the jar on a flat surface. After about half an hour the soil will
have settled, have a look at it and then shake it up again well. Leave the jar to settle
overnight.
Sometimes it helps to add a little salt (% or 1 tea spoon) to the jar because this helps to
separate the clay from the sand.
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