Modern Earth Building 2002 - Berlin
Earth Building in Australia - Durability Research
Gregory Moor & Kevan Heathcote
This paper looks at the development of Earth Building in Australia and the various types common in the country and outlines the research program undertaken by the authors into the durability of earth walled buildings.
According to Pollock (1999) the use of earth as a building material dates back to at least the Ubaid period in ancient Mesopotamia (5000-4000 B.C.). Easton (1996) has suggested that at least 50 % of the world's population still live in earth houses
There are basically three types of earth building techniques in Australia at the present time.
1. Mud Brick or Adobe . Adobe bricks are typically 250mm by 350mm by 100mm and are made by pouring a puddled mixture of clay and sand into forms. Modern developments have seen the introduction of mechanised equipment, which enables many blocks to be formed at once. Once laid the blocks are left in the sun to dry.
2. Rammed Earth or Pise. Although the technique is centuries old principally the French in the latter half of the 19th century developed this technique. The name pise is a shortening of the word pise de terre. In this method a dryish mixture of sandy soil is rammed into wall forms. The thickness of rammed earth walls is typically around 600mm but more recently walls built from earth stabilised with cement are being built with thicknesses around 300mm
3. Pressed Earth Bricks. This is a development of adobe, which surfaced in the second half of this century. In this method a dryish soil is placed in a steel mould and compacted under high pressure. Typically densities of around 2000 kg/m^2 are achieved compared to around 1700 kg/m^2 for traditional Adobe bricks.
In recent times many variations of the above three types have been marketed, an example being the poured earth method, where puddled clay is poured into wall forms rather than individual brick moulds.
The traditional adobe structure is coated with a protective weatherproof coating such as stucco and is therefore protected from erosion. Many examples of buildings built in France and Italy using this form of protection remain today after centuries of exposure to driving rain. Recently however it has been thought to be architecturally desirable in Australia to leave earth walls without any exterior coating, and this has given rise to questions as to long-term resistance to driving rain
The mid-50's saw a demand for more ' modern' houses in the Western World and earth building was relegated to undeveloped countries, being seen as a low cost-housing alternative.
With the advent of the energy crisis in the 70's earth building became popular in quite a few developed countries such as Australia, due to its low embodied energy and perceived thermal effectiveness. Unfortunately, as Fitzmaurice (1958) had found, unstabilised earth buildings require considerable maintenance unless adequately protected from driving rain by wide eaves and often this was contrary to the more modern architectural styles adopted in some western countries, where eaves have been minimized or eliminated.
Professional builders moved into the area and they brought with them a desire for a more consistent permanence, leading to an increase in the use of stabilisation, particular in the area of cement stabilised pressed earth bricks and rammed earth. Figure 1. shows a new campus for the Charles Sturt University at Albury in New South Wales, Australia, which is constructed entirely of cement stabilised rammed earth.
Figure 1. Stabilised Rammed Earth Building at Albury, NSW
EXTENT OF EARTH BUILDING IN AUSTRALIA
The following notice, inserted by the Agricultural Society on 10 May 1823, appeared on the front page of the Hobart Town Gazette.
'Resolved-that the mode of Building in Pise', or rammed earth, appearing to this Society to be both economical and expeditious, the Society earnestly recommend its Adoption in Van Diemen's Land'
Building with earth was not a new thing to the original inhabitants of Australia, for thousands of years prior to European settlement the indigenous Australian aboriginal people developed appropriate dwellings for their lifestyle and environment. Although examples of Aboriginal dwellings are no longer in existence early European authors describe them. The explorer Eyre wrote: we found a village of thirteen huts near mount Napier, they were cupola-shaped, made of a strong wood frame covered with thick turf. Figure 2 shows an Aboriginal hut similar to the ones Eyre discovered.
William Buckley an escaped convict described in 1803 how he was taken in by some Aboriginals whose huts were small turf cabins.
Figure 2. Aboriginal hut without its turf covering c1900
The first European settlers who arrived in Sydney Cove in 1788 were not aware of Aboriginal construction methods but soon found the small acacia trees were suitable for wattling and plastering with clay. The trees became known as wattles and the building process wattle and daub. Governor Philip began a new settlement at Parramatta and before the end of 1790 there were thirty-two houses completed, built of wattles, plastered with clay and thatched. Figure 3.shows a wattle and daub house similar to the ones constructed at Parramatta. The first church built in Sydney by the Reverend Richard Johnson was a wattle and daub structure with a thatched roof.
Figure 3. Wattle and Daub house with thatched roof and earth floor.
When a crossing was found across the coastal mountain ranges settlers moved to the grass plains beyond and as timber was scarce earth was again used for construction. An early reference is by the Reverend James Hassel who wrote in 1826: my father erected a house upon his land which after the usual fashion of the Bathurst district consisted of sod walls and a grass thatched roof. Apart from sod buildings on the plains the construction method of pise' was being introduced, the Reverend Hassel built a church and a barn between 1826 and 1831. The barn and 'Wanstead Park' in Tasmania are probably the oldest earth buildings standing in Australia, Figures 4 shows a restored pise' house in the Bathurst district of New South Wales.
Pise' and its modern derivative Rammed Earth has continued to be used extensively with many examples throughout Australia.
Figure 4. Pise' house near Bathurst c1850.
Adobe or mud brick construction developed from the mid 1800s, the Southern Australian reported in 1839 of this form of construction: nearly thirty houses have been erected.they are mostly built of pise', or of unburnt bricks, which have been hardened by the sun. Figure 6 shows a mud brick home in Victoria, c1890.
Figure 6. Mud brick home in Victoria 1890
For the next one hundred years earth building continued to be used in Australia, but with the increase in availability of baked bricks and milled timber it became less common and was mostly restricted to remote rural areas. One notable exception was in the outer Melbourne suburb of Eltham and in particular within its artistic community, where earth building continued to be used, mostly in adobe construction. Figure 7 shows one of the many earth buildings in the artist colony of Monstalvat, Eltham.
Figure 7. Montsalvat, Victoria. Artist's workshops constructed from 1935 with mud brick, wattle and daub.
Modern Earth Building
The most significant contemporary development in earth building occurred during the late 1940s and early 1950s through the efforts of G.F.Middleton an English trained Architect and Engineer. Middleton was employed in 1946 by the Commonwealth Experimental Building Station in Sydney where he began research on earth wall construction and as stated in the introduction to his book Build Your House of Earth ? the establishment of a well-tried technique for the identification of suitable earths, and a standard of practice for the methods of construction, should place earth wall construction, which has so much to commend it, high among the accepted building methods. Middleton's publication Bulletin 5, Earth-Wall Construction has been accepted in Australia as the standard reference in earth building, detailing soil selection, construction methods and testing procedures. This publication highlighted cement stabilisation of pressed block and rammed earth construction methods and contributed to the wide spread use of these techniques throughout Australia. The three common methods of earth construction, adobe, rammed earth and pressed blocks, have tended to be used in different areas, adobe is most common in Victoria (Figure 10), rammed earth in Western Australia (Figure 11) and pressed blocks in New South Wales. (Figure 12) This situation is more due to the development of local expertise than the inherent suitability of a method of construction to a particular area. As the various construction techniques are becoming more widely known the selection of the appropriate one to suit the area of construction is developing, this is particularly evident in the wide spread use of rammed earth in both domestic and commercial construction.
Figure 10 Adobe block cabin
Figure 11 Rammed Earth House under construction.
Figure 12 Pressed block, cement stabilised Tourist Information Centre.
DURABILITY RESEARCH IN AUSTRALIA
Due to their limited durability in an unstabilised state earth buildings have in the past been seen to be inferior to more permanent materials such as stones and fired clay bricks.
'We note also that in the United Kingdom and France that earth walling is limited to the smaller domestic and farm buildings. In the old villages the parish church and the manor house, and any buildings having more considerable architectural pretensions, were invariably built of brick or stone. Thus we may take as a tacit admission that unstabilised earth walling did not possess sufficient permanence to justify the expenditure of a large amount of effort and elaboration in fittings and decorative work.' (Fitzmaurice, 1958, p5)
The perceived lack of durability of earth has been a significant barrier to its acceptance as a modern building material. Major earth buildings that have survived over long periods are mainly located in areas of minimal annual rainfall, are protected by large overhanging eaves, or are covered with protective coatings.
Middleton (1952) constructed many rammed earth test walls at the Commonwealth Experimental Building Station in Sydney in 1949. What these experiments demonstrated, after 43 years of exposure, was the dramatic effect climatic conditions have on the durability of earth walls. Figure 12 shows the north and south faces of one of Middleton's rammed earth panels, clearly indicating the pre-dominance of wind-driven rain from the southerly direction.
North Face South Face
Figure 12: Rammed Earth Panels at Experimental Building Station
At the same time as professional builders were recognizing the potential of earth as a building material, standard codes of practice were moving towards performance based specifications. Requirements for durability testing present in earth building codes had been developed in specific localities and were not readily transportable to regions where the climatic conditions were significantly different. To satisfy the requirements of performance based codes it became necessary to understand the effect various climatic parameters have on the durability of earth walls.
Research being carried out at the University of Technology Sydney by the authors has been aimed at providing a methodology whereby the performance of specimens in the laboratory can be related to performance in the field, with the aim of providing a performance based design criteria which is linked to the location of the intended structure. Initially a small earth structure was constructed with pressed cement stabilised blocks in 1992. The erosion of this structure has followed the same pattern as the Middleton specimens with the south face showing the most significant effect (Figure 13). Continuing work involves placing specimens in the field (Figure 14), after subjecting 'identical' split face specimens to spray testing in the laboratory (Figure 15).
'Figure 13. Test structure constructed at University of Technology.
'Figure 14. Specimens in Test Rack
Figure 15. Spray Test Apparatus
Climatic conditions, measured in the field, were then correlated with the hydraulic characteristics of the laboratory spray test, providing a relationship between the two sets of specimens. This work is almost complete and indicates that it is possible to predict with reasonable accuracy the performance of specimens in the field based on their laboratory test results.
The 'Limit State' concept being developed from this research means that unlike other materials where the erosion resistance is fixed (such as fired clay bricks) the design of earth walls offers the designer the opportunity to uniquely match the erosion resistance of the material with the factored climatic loading.
Earth building has a long history in Australia and there is an active interest in continuing to develop this form of construction. There is an active earth building association and considerable research is being done to further understand the properties of earth as a building material.
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Fitzmaurice, R. 1958 Manual on Stabilised Soil Construction for Housing, Technical assistance Program, United Nations.
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Middleton, G. F. 1953, Build Your Own House of Earth, Compendium, Melbourne, Australia.
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 The popular Spanish word for mud brick, originating from the Arabic word al-tob