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Frequently Asked
Questions
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What
foundations can
be used?
This depends on the
stability of the
substrate. If
the earth has never
been disturbed and
is very compact down
to at least 500mm,
then it is possible
that a simple
EarthBag foundation
can be used.
This in essence is a
very shallow trench,
the depth of 2
layers of EarthBags,
and the bags in
these layers and
another 2 rows above
ground level are
filled with a
stabilised sand /
cement mix.
We have used this
system on an
extremely unstable
site in Cape Town
(by necessity, not
choice), and the
house is in
excellent condition
2 years later, with
no cracking of the
plaster (see below
for answers to plaster
application
questions).
Considering this
very poor site, the
simple foundations,
unstabilised sand in
the EarthBags with
plaster directly
applied and no use
of wire mesh, this
is an impressive
result. Even
had there been
cracking, it would
have been of a
cosmetic nature
only, and not
structural as it
would be with brick
or block. Had
the latter materials
been used, the house
might well have been
demolished by now.
Why is this
possible?
It is due to the
elastic but
monolithic mass
characteristics
of EarthBag
walls. Any
movement is
dispersed by the
millions of
particles of
sand, and the 2
plaster layers
can move
independently of
each other.
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What is special
about our EarthBags, what are they made of and how
long will they last?
The bags are a unique
patented design that allow for interlocking of horizontal
layers greatly adding to the stability of the wall.
This design also allows for accurate and equal filling,
relatively low mass at approximately 13kg, uniform
horizontal layering in the wall, easy construction of
integrated lintels and ring beams and laying of conduits
both vertically and horizontally.
All of these advantages are reasons the EarthBag is made the
way it is. Using a standard polypropylene fertiliser
bag, it is possible to construct a wall, but the ease of
build, the end result and the ultimate strength are all very
adversely affected. For example, the bag will be very
heavy and therefore needs to be filled in place on the wall,
it is difficult to fill every bag to the same degree, and to
get the bags to lie symmetrically takes experience.
Furthermore, with a standard bag, one bag lies directly on
the one below, plastic on plastic, with minimal lateral
stability, and increased chance of slippage. Barbed
wire then has to be used to 'velcro' the layers together.
Using sand alone with these bags is not a good option, so
stabilising with cement or using a clay-earth mixture is
required.
How is this system different to other sandbag / wood-beam
systems in South Africa?
The EarthBagBuild system uses no frame, wood or steel, apart
from a amall amount of rebar in the integrated lintel
system, if it is used.
This means that the only 2 materials in the wall are
polypropylene and earth. There is no wood to rot nor
steel to corrode. Given that ideally there should be a
6-8% humidity in the wall which, with a porous plaster and
paint system, will regulate the humidity in the house, any
wood and steel is likely to degrade sooner rather than
later. Even treated wood will be susceptible and with
the galvanised steel lattice that is used in another system,
since the galvanising is pierced every 15cm, the beam must
fail at some point due to corrosion.
Given that this other system relies on these beams for its
structural strength, it seems that these beams are a major
disadvantage in a wall building system.
Furthermore, the small 30 x 30 cm bags of fragile non-woven
polypropylene are often placed in vertical stacks, as this
is how they easily fit into the 90 cm space between vertical
beams. So one often does not have any 'running masonry
bond' or overlap of the bags. The wall is then divided
into 90 cm panels by these vertical beams. All in all,
not an ideal structural design.
The other advantage is that no mesh is required over the bags to
aid adhesion of the plaster. Partly the reason for
this is that the woven polypropylene used in the EarthBag
system is extremely strong, unlike the easily torn non-woven
material in the beam-sandbag system. The
bond achieved by plastering directly over these woven
polyprop EarthBags is excellent - note our reference to the
pilot project in Masiphumelele under the 'foundation'
paragraph above. There is a simple process for
preparing the surface of the bags that we recommend to
achieve very strong adhesion, though strictly speaking it is
not absolutely necessary.
Other FAQ's to follow soon!
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