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Are
earth walls expensive? |
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The wall
component of the average house comprises around 12 - 15% of the total
cost. In Western Australia, a wall of 250mm thick double brick, faced one
side and plastered the other, will be around 3% (of the total cost)
cheaper than 300mm thick monolithic stabilised earth walls. Designing
specifically for earth walls will always be a significant factor in
keeping costs down.
Stabilised Earth is the most efficient of the various techniques of building earth walls, in terms of the amount of labour required to produce a volume of walling. It is consequently the most cost effective way of building high thermal mass walls. The a s E g pricing system is open and straightforward. You will
receive a quote for 'face square metres' of wall shown on the plan, and
the price includes all materials, equipment and
labour. | |||
| What
about waterproofing? | |||
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To achieve a
natural finish, monolithic stabilised earth walls stand as they appear out
of the formwork that moulds them. Silicone-based sealants provide the most
effective waterproofing treatments. They allow the wall to 'breathe', and
are invisibly absorbed into the wall rather than remaining on its surface.
'a s E g Plasticure' is a silicone-based emulsion developed specifically for the Affiliated Stabilised Earth Group. An admixture, its addition during wall construction reduces water absorption by over 80% during the life of the structure, as well as increasing the compressive strength of the walls by up to 50%. aP is added along with water at the mixing stage, becoming permanently bonded to the substrate, and it won't break down under exposure to ultraviolet radiation. Stabilised Earth is basically a damp soil - cement mix compacted in
situ into prepared formwork, and has more in common with poured concrete
than with mud brick or cob. It is technically a variation of concrete and
can be designed and engineered as mass concrete, commonly with compressive
strength of 6 to 8 MPa. | |||
| What
Standards and Specifications do members of a s E g work
to? | |||
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The Building
Code of Australia 1996 identifies sections of 'CSIRO Bulletin 5 -
Earthwall Construction' (fourth edition) as deemed-to-satisfy performance
requirements.
In specifying, the nationally recognised standard in Australia is Construction Information Systems Australia Pty Ltd's NATSPEC (the National Building Specification), which now includes a section on Monolithic Stabilised Earth Walling.
a s E g will also supply its own specification which has been developed
by engineers, architects and builders working throughout Australia over
the last twenty years. | |||
| Stabilised Earth or Rammed
Earth? | |||
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Contemporary
monolithic stabilised earth walling is derived from traditional rammed
earth (pise). An Australian, George Middleton,began experimenting with
stabilised earth walls in the late 1940's and introduced the term in the
"Experimental Building Station Bulletin no. 5", published in 1952. In his
role as adviser on low cost housing, he introduced the concept to the
Israelis in 1953. Subsequent Israeli developments were published in "Soil
Construction - Its Principles and Application for Housing" in 1957 by S.
Cytryn. In an historic rebound, this book set the course for architect Tom
Roberts' and Giles Hohnen's developments that started in Margaret River,
WA in 1976.
Since then Stabilised Earth has become accepted as a generic term and the product has gained a small but enthusiastic niche market in Australian design and building, particularly in the market concerned with climate sensitive and energy efficient building. Builders of stabilised earth are now active throughout the country. There is variation in formwork systems and handling methods, but most operators use skid steer loaders to mix and deliver material to set formwork into which material is hand shovelled and then compacted with pneumatic tampers. Variations in the amount and type of formwork used, soil selection and stabilisation techniques, moisture content, mix working times and curing times make considerable differences to the resultant product of different operators, viz., accuracy, surface stability and texture. In the early 1980's a number of stabilised earth builders who had grown from the beginnings in Margaret River formed what is now the "Australian Stabilised Earth Group" ASEG's aim was to develop stabilised earth building towards a more commercial industry, with members sharing a standardised equipment system, methods, information, promotion strategies and engineering. ASEG members have produced the majority of stabilised earth building in the last 20 years as well as accumulating the largest body of relevant data; soil specifications, construction details, engineering and design data. The specification and regulation of the stabilised earth industry has progressed as this data has been collected and made available to engineers and regulating authorities. The de facto reference for earth building, "CSIRO EBS Bulletin 5", derived from Middleton's experimental work from the 40's, had been becoming increasingly redundant in light of the testing and experience available from the last 20 years' work. The "NATSPEC Specification for Monolithic Stabilised Earth Walling" was a turning point in providing a reference advised by the results of this work and has given engineers, designers and regulators a superior tool, in the absence of an Australian Standard. Whether this tool is used to achieve more consistent standards in stabilised earth building depends on how rigorously it is applied. Standards Australia have recently released "The Australian earth building handbook HB195", which in relation to the NATSPEC spec. is a vague and generalised regulating tool, to suit a wider range of operators and methods. HB 195 contains descriptions of how stabilised earth walls might be built, but contains less practical instruments by which methods can be defined and controlled and its adoption would result in an increase in the variation in quality standards in the industry. | |||
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