|Small-Scale Manufacture of Stabilised Soil Blocks (ILO - WEP, 1987, 204 p.)|
This technical memorandum on small-scale production of stabilised soil blocks is the ninth in a series of memoranda currently being prepared by the ILO and UNIDO.1 It is the second of three memoranda on building materials for low-cost housing.2
1 Three other memoranda have been published jointly with FAO and UNEP.
2 One technical memorandum on small-scale brickmaking (Technical Memorandum No. 6) has already been published. Another memorandum on the small-scale production of windows and doors for low-cost housing will be available in 1987.
This technical memorandum is of particular importance to developing countries in view of the current severe shortage of shelter for large sections of the population in these countries. Yet, after food and clothing, adequate shelter is one of the most important basic needs. It is estimated that one-fourth of the worlds population does not have adequate housing. An average of 50 per cent of urban populations live in slums. In some developing countries, urban slums constitute up to 80 per cent of urban settlements. The housing situation in developing countries will further deteriorate unless substantial resources are allocated to this sector by governments and international aid. This explains the decision of the United Nations General Assembly formally to proclaim 1987 as the International Year of Shelter for the Homeless (IYSH), with a view to securing renewed political commitment and effective action within and among the international community. The International Labour Office will contribute, in the future, to the achievement of the above objectives, especially since the implementation of appropriate housing policies will also generate a great number of much needed employment opportunities. It is hoped that the preparation and dissemination of this memorandum will be helpful in formulating such policies.
Developing countries wishing to expand substantially the housing stock for low-income groups will have to identify the least costly solutions, in terms of unit housing cost and the foreign exchange content of such cost. Furthermore, these solutions should allow, whenever possible, the direct involvement of potential home owners who may wish to contribute their labour in, for example, self-help housing schemes. The use of soil as an alternative building material for a wide range of housing types should be part of these solutions, and should be promoted by housing authorities for the following reasons.
Firstly, soil is already being used as a main building material by a very large number of developing countries but is often considered as a second-best or poor-mans solution. Thus, whenever financially possible, there is a tendency to switch to other building materials which are considered more modern (e.g. concrete) than soil. It is therefore important to reverse this trend by demonstrating that properly processed soil is as good as, or even better than, these modern materials.
Secondly, houses built with blocks of stabilised soil are often less expensive than those built with other materials, such as concrete blocks or wood. Thus, the use of soil should facilitate home ownership and minimise government subsidies for low-cost housing projects.
Thirdly, the use of soil requires substantially fewer imported inputs than many other building materials, and should therefore contribute to an improvement in the balance of payments situation of developing countries.
Fourthly, the building of a housing unit with stabilised soil will often generate more direct and indirect employment than if the same housing unit was built with other materials, such as concrete or fired bricks.
Finally, houses made of stabilised soil often offer a more pleasant environment (e.g. in terms of protection against outside heat or cold) than houses made of the so-called modern materials.
From many points of view - technical, cultural, environmental, financial - soil could be given preference as a building material. In order to expand the use of this material, housing authorities will need to implement three groups of measures. The first group relates to the improvement of housing design and construction processes. It has now been proved that soil can be a sound building material if properly used. A large number of experiments have been successfully conducted throughout the world, the techniques and tools have been improved and technical solutions have been found for the three main problems which militated against the use of soil as a building material: the deterioration of earth walls by rain; low resistance to earthquakes; and the difficulty of building floor slabs. Furthermore, the maintenance of earth buildings may be considerably reduced and their lifespan increased if appropriate designs are used and raw materials adequately processed. A large number of construction projects completed under a wide range of climatic conditions in both developing and developed countries demonstrate that there are currently no unsolvable problems in the use of earth as a building material. Housing authorities therefore need to promote research in this field, disseminate technological information on earth building techniques, and provide training facilities - at all levels - for the proper processing and use of soil for building.
The second group of measures relates to the government policies required to induce individuals and contractors to adopt soil-based materials in housing projects. Housing authorities would need to advise the central Government to formulate and implement fiscal and monetary measures in favour of the adoption of earth as an alternative building material. For example, higher duties could be applied on imported materials and higher housing subsidies could be granted for earth buildings. Preference could be given to contractors bidding for government-financed projects (e.g. construction of schools) whenever they offer to use earth as the main building material.
The third group of measures relates to the dissemination of information on the utilisation of earth as a building material. Such information should dissipate doubts on the technical and economic efficiency of this material and improve the image of earth buildings among those who may feel that the use of earth for building purposes is a second-best solution for countries which may not be able to afford the so-called modern materials. It is hoped that the information contained in this technical memorandum will help achieve these goals.
The ILO is not the only institution promoting the use of soil for buildings. Currently, a large number of centres in both developing and developed countries are vigorously promoting this material for all types of building; low and middle-income housing, luxury houses, office buildings, religious buildings, and so on. These centres are located both in the North and in the South, on all continents and under a wide range of climates (see Appendix II). The proliferation of such centres is indicative of the renewed interest in earth as an alternative building material. It is interesting to note that a few days before this memorandum was being sent for print, the use of earth as a building material was the main topic of a popular television programme in France.3
3 This programme, entitled Ambitions, went on air on 3 December 1986.
As in the case of the other technical memoranda, the main objective of this memorandum is to provide small-scale producers in developing countries with detailed technical information on small-scale technologies which have been successfully applied in a number of countries, but are not well known in others. A secondary objective is to assist public planners in identifying and promoting technologies consonant with national socio-economic objectives, such as employment generation, foreign exchange savings, rural industrialisation, or the fulfilment of the basic needs of low-income groups.
The information contained in this memorandum is sufficiently detailed for small-scale producers to identify and apply the technologies described in the text without the need for further information. Thus, detailed drawings of equipment which may be manufactured locally are provided and a list of equipment suppliers from both developing and developed countries is annexed in order to help producers choose the equipment which must be imported. In the few instances where the available information is not sufficient, the reader may obtain additional technical details from publications listed in the bibliography.
Technical memoranda are not intended as training manuals. It is assumed that the potential users of the technologies described therein are trained practitioners, and that the memoranda are only supposed to provide them with information on alternative technological choices.
This technical memorandum contains eights chapters, five of which deal with the various sub-processes needed for the manufacture of stabilised soil blocks, including quarrying and testing of raw materials; pre-processing of the latter (grinding, sieveing, proportioning, and mixing); block forming methods including a detailed description of alternative block forming machines; curing and testing of blocks; and the use of mortars and renderings in wall construction. The last chapter (Chapter VIII) is mostly intended for public planners and project evaluators from industrial development agencies who wish to obtain information on the various socio-economic effects of the production and use of alternative building materials.
The memorandum also contains four appendices which could be of interest to the reader. Appendix I provides a glossary of technical terms, and should therefore be of assistance to non-specialists. Appendix II provides a list of institutions from which additional information on earth building techniques may be obtained. Appendix III provides a list of equipment suppliers and manufacturers from both developing and developed countries. It may be noted that this list is far from being exhaustive and that it does not imply a special endorsement of these suppliers and manufacturers by the ILO or UNIDO. The names listed are only provided for illustrative purposes and readers are urged to obtain additional information from as many sources as possible. Appendix IV provides a bibliography on the subject, which may be useful in learning more about the techniques described in the main body of the text.
A questionnaire is attached at the end of the memorandum for those who may wish to send to the ILO or UNIDO their comments and observations on the content and usefulness of this publication. These will be taken into consideration in the preparation of future technical memoranda.
The memorandum was prepared by R.G. Smith and D.J.T. Webb, staff members of the Building Research Establishment (United Kingdom) in collaboration with M. Allal, staff member in charge of the preparation of a series of technical memoranda within the Technology and Employment Branch of the International Labour Organisation. The preparation of this memorandum also benefited from very useful information and suggestions provided by a large number of individuals and institutions. The ILO, UNIDO and the authors acknowledge their generous assistance.
Technology and Employment Branch.