Civil Engineering Reference
In-Depth Information
more confusing when you read topics about
earth plasters, using dirt for plastering, etc.
The fact is that in many parts of the world
there is almost no topsoil, and you can
basically dig away at the earth, add straw
and water to it and make it into a great
plaster or use it to build walls with, hence
the terms 'earth plaster', 'earth walls' or
'dirt plaster'. This is not the case in the UK
and Ireland, however, because even in
places where we can take away the topsoil
and just use what's underneath, it's almost
always far too wet and sticky to use without
some sort of processing.
In the UK and Ireland, pretty much any type
of clay that you find can be used for plastering,
usually with the addition of some sand and
fibre.
As clay is made from local rocks, weathered
by rain, as well as being carried by water
long distances, it's quite possible to find a
pocket of clay in one area that is completely
different from another pocket only half a mile
away. Depending on the geology of your
local area, you may find a clay subsoil that
is ideal for plastering, or pockets of clay that
can be added to sand to make a good mix.
Clays have different properties because of
the rocks they are made from. China became
famous for its little yellow clay pipes, made
from 'China clay', a type of clay that can be
fired at high temperatures and makes very
fine scientific instruments.This is also the
source of the clay in the old-fashioned diges-
tive remedy, kaolin and morphine; it comes
from the area in China near Mount Kao-Ling.
It's always important to take away the topsoil
first. This is the growing medium that
contains organic matter such as plant roots
and worms, and can't be used to make a
plaster. If you dig a hole, underneath the
topsoil you should find you come to a layer
of undisturbed ground, and this is the
subsoil. If it's clay-rich, then you can certainly
use it for construction, both for house build-
ing and for renders and plasters, but it will
probably need to have water mixed into it
first to make it usable, and it may also need
sand and fibre adding.
We are also familiar in everyday life with
another clay, but one that would definitely
not be good for plastering - Fuller's earth,
better known as natural cat litter. This is a
clay that expands dramatically on contact
with liquid - not something we would want
our plaster to do! Understanding the nature
of clay is a science all of its own, as clays
are made up of many different substances.
For our purposes, it is enough to say that
all
home-made clay plasters should be tested
before use
to work out exactly what mix of
subsoil, sand and straw should be used.
In the UK and Ireland, pretty much any type
of clay that you find can be used for plaster-
ing, usually with the addition of some sand
and fibre. It's common to find it in river
banks in the slow parts of the stream, and
in areas that thousands of years ago were
estuaries, because, as a very small particle,
clay takes a long time to settle out of water,
so needs almost still water to do this in.
