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CLOSE THIS BOOKSmall-Scale Brickmaking (ILO - WEP, 1984, 228 p.)
CHAPTER I - INTRODUCTION
VIEW THE DOCUMENTI. Purpose and objectives of the memorandum
VIEW THE DOCUMENTII. Target audience
VIEW THE DOCUMENTIII. Comparison between bricks and other building materials
VIEW THE DOCUMENTIV. Scales of production covered by this memorandum
VIEW THE DOCUMENTV. Content of the memorandum

Small-Scale Brickmaking (ILO - WEP, 1984, 228 p.)

CHAPTER I - INTRODUCTION

I. Purpose and objectives of the memorandum

Housing constitutes one of the most important basic needs of low-income groups in developing countries. However, it is the most difficult to satisfy as land and building costs are often outside the means of the unemployed and underemployed in both rural and urban areas. Thus, many governments have launched various schemes with a view to facilitating housing ownership by low-income groups, including self-help housing schemes, granting of housing subsidies, provision of credit at low interest rates, etc. Given the limited means at the disposal of governments and potential home owners, it is important to seek ways to lower the cost of low-income housing while minimising repair and maintenance costs. In particular, governments should promote the production and use of cheap yet durable building materials as the latter constitute a very large proportion of total low-income housing costs in developing countries (1). Furthermore, it would be useful if the production of these building materials could contribute to the fulfilment of important development objectives of these countries, such as the generation of productive employment, rural industrialisation, and a decreased dependence on essential imports.

A number of traditional building materials exist which have proved themselves to be the most suitable materials for use in a wide variety of situations, and have a great potential for increased use in the future. These traditional materials, which make use of locally available raw materials, can be manufactured close to the construction site with little equipment (which may be produced locally), and are often more appropriate to the environment than modern materials. One such building material is clay bricks. The purpose of this technical memorandum is to provide detailed technical and economic information on small-scale brick manufacturing with a view to assisting rural and urban entrepreneurs to start up new plants or improving their production techniques. It is also hoped that the information contained in this memorandum will help slow down the establishment of large-scale, capital-intensive plants which are not always suitable to socio-economic conditions of developing countries.

I.1 Need for improved brick production techniques

Various production methods are used for brickmaking in developing countries. Traditional hand digging, moulding and handling are used by a large number of small production units. Some larger units tend to use equipment for digging or mixing, while a number of developing countries have chosen to import large-scale capital-intensive plants.

The choice of brickmaking technology is mostly a function of market demand (e.g. scale and location of demand, required quality standard), availability of investment funds, and unit production costs associated with alternative production techniques. In some cases, governments may also impose various policy measures with a view to favouring the adoption of techniques consonant with the national development objectives. Whatever the adopted technique, quality may be improved and costs reduced if appropriate measures are taken during the production process.

Experience shows that a large fraction of bricks are often wasted during the various production stages. For example, moulded bricks get eroded by the rain before firing or distorted by bad handling methods. Sometimes, incorrectly adjusted machines yield inconsistent or inferior output which may not be marketed. With attention to the basic principles of brickmaking and more care, a greater number of bricks could be produced for the same expenditure of labour, raw materials and fuel.

In some instances, more careful preparation of raw materials would minimise problems at subsequent manufacturing stages. For example, if stones or hard dry lumps of clay are included in the moist clay used for moulding, they will exhibit different drying shrinkages from the moist clay and give rise to cracks in the dried or fired bricks. The remedy in such a case would have been to select a more uniform raw material, or to remove the offending particles, or to break the material down to a fine size (e.g. by manual means or with a crushing machine).

Use of a good product, of regular shape and size and of consistent properties, will enable the accurate building of walls while minimising the use of mortar between bricks. Renderings, often applied in developing countries, will also require less mix for a given wall area if the brickwork face is accurate. Alternatively, if the brick quality is sufficiently good, it may be unnecessary to apply renderings at all. A good product will thus favourably impress the customer and save materials, time and money. It should therefore improve future demand for the product. Good bricks should be durable and brickwork should be long lasting.

I.2 Availability of information on brickmaking

The techniques of brickmaking are often handed down from father to son in small works, or are taught in various technical schools, training centres, etc. Articles and books have been published(2) but are often too brief or mostly concerned with large-scale production, scientific investigations or laboratory tests. They also often relate to conditions and needs of the more developed countries. With few exceptions(3), there is a lack of information on practical details of small-scale production in rural or peri-urban areas.

Information on sophisticated high capital cost brickmaking plants can be obtained from published books and scientific and trade journals, or from equipment manufacturers and consultants. On the other hand, it is more difficult to obtain information on small-scale, labour-intensive production. Many appropriate technology institutes, building research centres and university departments do generate information on appropriate production techniques (see list in Appendix III). However, this information is either not published or is not disseminated to other developing countries. This memorandum seeks, therefore, to provide information on small-scale brickmaking with a view to partially filling the current information gap. It does not provide technical details on all possible circumstances, but will, it may be hoped, induce small-scale producers to try production techniques which have already been successfully adopted in a number of developing countries.

II. Target audience

This memorandum is intended for several groups of individuals in developing countries, including the following:

- small-scale brickmaking producers in rural and urban areas, and those considering starting brick production. These could be either individual entrepreneurs or groups of artisans associated in a manufacturing co-operative. These producers will be mostly interested in the information contained in Chapters II to VII, and Chapters IX and X.

- housing authorities, public planners and project evaluators in various industrial development agencies may be interested in the information contained in Chapters II and XI. This latter chapter, which focuses on the socio-economic implications of alternative brickmaking techniques, will be of particular interest to public planners concerned with employment generation, foreign exchange saving, etc.

- financial institutions, businessmen, government officials and banks should be mostly interested in Chapter X which provides the necessary information for costing alternative production techniques.

- handicraft promotion institutions, village crafts organisations and equipment manufacturers should find the technical chapters II to VII useful.

- voluntary organisations, foreign experts, extension workers and staff of technical colleges will wish to compare bricks with other building materials, as detailed in Chapter I (section III). They may also benefit from the technical information contained in Chapters II to VII.

It must be stressed that this is not a technical memorandum on the use of bricks in building, although some of the information contained in Chapter VIII may be of interest to builders.

III. Comparison between bricks and other building materials

This section compares the properties of fired clay bricks with those of other alternative walling materials. Table I.1 gives specific values for some of the properties discussed below. This comparison should be useful to housing authorities in deciding which building materials should be most appropriate for various types of housing or housing projects.

III.1. Strength

Compressive strength of fired-clay bricks varies enormously, depending upon clay type and processing. Strength requirements for single-storey housing are easily met.

Calcium silicate bricks, made from sand with high silica content and good quality, low magnesia, lime, may have strengths approaching those of good fired clay bricks. However, high capital cost machinery is used for the mixing, pressing and autoclaving. Furthermore, calcium silicate bricks must be produced in large-scale plants.

Concrete bricks and blocks have sufficient strength, but require cement which is expensive, and must often be imported.

Lightweight concrete blocks, made with either natural or artificial lightweight aggregate, have adequate strength but require cement.

Aerated concrete has low strength which may be sufficient for one-storey buildings. Particularly careful production control is necessary, using autoclaving to reduce subsequent moisture shrinkage of blocks made from this material.

Many types of soil have sufficient compressive strength when dry. However, this strength is considerably reduced once they become saturated with water.

Table I.1

Range of properties of bricks and blocks

Property

Fired clay bricks

Calcium silicate bricks

Dense concrete bricks

Aerated concrete blocks

Lightweight concrete blocks

Stabilised soil blocks

Wet compressive strength
(MN/m2)

10 to 60

10 to 55

7 to 50

2 to 6

2 to 20

1 to 40

Reversible moisture movement (% linear)

0 to 0.02

0.0l to 0.035

0.02 to 0.05

0.05 to 0.10

0.04 to 0.08

0.02 to 0.2

Density (g/cm3)

1.4 to 2.4

1.6 to 2.1

1.7 to 2.2

0.4 to 0.9

0.6 to 1.6

1.5 to 1.9

Thermal conductivity
(W/m°C)

0.7 to 1.3

1.1 to 1.6

1.0 to 1.7

0.1 to 0.2

0.15 to 0.7

0.5 to 0.7

Durability under severe natural exposure

Excellent to very poor

Good to moderate

Good to poor

Good to moderate

Good to poor

Good to very poor

Waterproofers such as bitumen, or stabilisers such as lime or cement, may be used with certain soils to improve wet strength. On the other hand, the strength of the other previously mentioned materials is only reduced slightly when they are wetted.

Gypsum, which occurs as a soft rock, or in some places as a fine sand, can be converted to plaster by gentle heating and then mixed with fine and coarse aggregate and cast into building blocks(5). Strength will be adequate for single-storey constructions, though wetting will reduce compressive strength to 50 per cent of the dry value.

Thus bricks are seen to be at the top of the list for strength, especially when wet.

Many other walling systems exist, notably panels made either from woven plant leaves or stems, or manufactured from cement, plastics, wood or metal. However, the strength of walls made from these panels will depend largely upon the frame which is built to hold them.

III.2. Moisture movement

Most porous building materials expand when wetted and contract again as they dry. Excessive movement can cause spalling, cracking or other failures in buildings. This reversible expansion is very small in fired clay bricks. However, a slow irreversible expansion commences as soon as bricks leave the kiln. This irreversible expansion may vary from virtually zero to 0.1 per cent linear movement. Under normal circumstances much of this expansion will have taken place before bricks are built into walls. Thus, the remaining expansion is likely to be insignificant in the context of small buildings(6).

Properly made calcium silicate bricks and concrete bricks are unlikely to have more than a fairly small amount of moisture movement. However, lightweight and aerated concrete units exhibit a greater movement. This sometimes leads to shrinkage cracking in buildings as they dry out initially.

Soil, especially plastic clay, may have a very large moisture movement of several percentage points. This is a major cause of failure in earth building. The problem is reduced if stabilisers are incorporated into the soil.

Timber, bamboo and other plant materials exhibit variable, but sometimes large, moisture movements. The latter take place especially across the grain rather than in line with it.

Moisture movement becomes especially important when two materials with different movement characteristics are in close juxtaposition in a building. Differential movements give rise to stress which may be sufficient to break the bond between the materials, or lead to other damage. For example, cement renderings often become detached from mud walling, and gaps appear sometimes between timber frames and infill materials.

Bricks thus compare favourably with alternative construction materials. Moreover, brickwork can be built without timber frames, thus excluding the possibility for differential movements.

III.3. Density and thermal properties

Fired clay bricks are amongst the most dense of building materials. This high density may constitute a disadvantage for transportation over long distances or in multi-storey framed buildings where the loads on frames would be high. On the one hand, weight is of little consequence whenever bricks are produced locally for close-by markets and single-storey buildings. On the other hand, the high density of bricks has the advantage over lightweight building materials of greater thermal capacity. This characteristic is sought in the tropics where extremes of temperature will be moderated inside buildings made of bricks.

Aerated and lightweight aggregate concretes have good thermal insulating properties but lack thermal capacity, while thick mud walls have fairly good insulation and good thermal capacity. Lightweight cladding materials, such as woven leaves and matting, metal sheeting and asbestos cement sheeting, have neither high insulation nor high thermal capacity.

Thus, bricks are particularly advantageous for low-cost housing as they considerably improve environmental conditions within the building.

III.4. Durability, appearance and maintenance

Evidence for the excellent durability of brickwork may be seen in many countries of the world. In the Middle East, brickwork 4,000 years old still remains. Bricks made 2,000 years ago in Roman times are still in use today. Indeed, properly made bricks are amongst the most durable of materials, having typical properties of ceramics such as good strength, resistance to abrasion, sunlight, heat and water, excellent resistance to chemicals and attacks by insects and bacteria, etc. If bricks are not well made (e.g. if the time or temperature in the kiln is insufficient), these desirable ceramic properties will not be developed, and performance will be nearer to that of mud bricks. Furthermore, to achieve the best performance from brickwork, attention must be paid to the correct formulation and use of mortar. Fired clay brickwork should sustain the adverse impact of the environment without the need of any surface protection (e.g. rendering). No maintenance should be required subsequent to building.

In some communities it is traditional to render the brick wall surface, although this is not necessary from either the appearance or performance point of view. Furthermore, lime washing on rendering is often used to achieve a white finish. A white finish is beneficial in reducing solar gain. It may be applied directly on the bricks without rendering, thus saving materials.

Other brick and block materials may also have good durability, if well made. However, the lightweight aggregate, aerated concrete and mud bricks normally require rendering to improve resistance to water.

The ultra-violet component of sunlight causes deterioration of many organic materials. These include timber and other plant-derived materials, plastics, paints, varnishes and bitumen. Inorganic materials, such as bricks, are immune to sunlight deterioration.

Termites occur in many developing countries and can attack and damage soft materials such as various species of timber. Other insects also attack timber. Hard materials such as bricks are entirely resistant.

Under damp conditions, timber and many other organic materials may rot through attacks by fungi, moulds and bacteria. Although some plant growth and mould may be seen on porous inorganic building materials, especially in hot-damp climates, damage is unlikely.

Fire can quickly destroy many building materials such as timber, woven matting and plastics. Cement products do not burn, but high temperatures in fires could break down some of the calcium and alumino silicates of which they are composed, causing loss of strength. In practice concrete may successfully sustain somewhat elevated temperatures without serious effect, though if concrete contains siliceous aggregates, such as flint, it is likely to spall(7). Reinforcing steel and steel frames lose strength and distort in fire, but are normally encased, and are thus protected to a large extent. Although clay brickwork could spall, crack and bulge in a severe fire, bricks are less likely to suffer damage than concrete and calcium silicate bricks as they have already been exposed to fire. Sudden cooling of hot areas by quenching with water in the course of fire-fighting may cause spalling. This does not generally affect the strength and stability of the brick wall seriously.

III.5. Earthquake areas

In general, bricks and blocks, whether of fired clay, calcium silicate, concrete, or stabilised soil, require steel reinforcement in seismic zones. Mud building, lightweight concrete and aerated concrete materials will also be at risk in these areas if not similarly reinforced.

III.6. Production cost and foreign exchange

The production costs of various building materials depend upon raw materials prices, methods used, markets, etc. which vary from time to time and place to place, making comparisons difficult. However, bricks are often amongst the cheapest of walling materials. It should be borne in mind that if, as stated at a United Nations Conference, a house is to retain its usefulness, it must be maintained, repaired, adapted and renovated. Thus, choices concerning standards, materials and technology should consider resource requirements over the whole expected life of the asset and not merely the monetary cost of its initial production(8). Durable materials such as bricks have a cost advantage in this respect.

The production of bricks from indigenous clays, especially if labour-intensive methods are used to avoid importation of capital-intensive equipment, will conserve foreign exchange. This is in contrast with some of the alternative materials.

IV. Scales of production covered by this memorandum

Bricks manufacturing may be undertaken at various scales of production, depending upon local circumstances. Table I.2 summarises the production techniques used at small, medium and large scales of production.

Table I.2

Scales of production in brick manufacturing

Scale of production

Number of bricks per day
(average)

Example of process used

Appropriate for market area

Small

1 000

Hand made, clamp-burnt

Rural village

Medium

10 000

Mechanised press, Bull’s trench kiln

Near towns

Large

100 000

Fully automated
Extruded wire cut, tunnel kiln

Industrialised areas of high demand and well-developed infra-structure

This memorandum is concerned primarily with small-scale production, though some consideration is given to medium-scale. Large-scale will be mentioned briefly for comparative purposes.

IV.1 Small-scale concept

A small brickworks producing 1,000 bricks per day may supply enough bricks each week for the building of an average size house. This may be adequate in a small village community. However, if demand were to increase suddenly, production could be increased to several thousand bricks per day merely by making additional wooden moulds and hiring more workers. In this case, the management staff does not need to be expanded. This larger production unit might also be established in small towns. Conversely, at times of recession or when weather prevents construction work, the demand will fall and production can be reduced temporarily. Thus, such small-scale industry is very adaptable to a changing market.

Small-scale production should be undertaken near the clay source, and within a short distance of the area where bricks will be sold and used. This will reduce transport cost while saving fuel. Small-scale production will not unduly spoil the landscape nor cause excessive pollution. An electricity supply may not be necessary and fossil fuels need not be used. Kilns may utilise waste materials for fuel, such as saw dust, rice husks, animal dung and scrub wood. The small works will provide employment within the local community. Capital investment is low for small-scale production and is thus appropriate for poor communities. Furthermore, equipment for small-scale brickmaking can be made and repaired within the local community.

IV.2. Large-scale concept

In contrast to the points mentioned above, the introduction of large brickworks necessitates capital investment of millions of dollars, mostly in foreign exchange for the import of the sophisticated production machines and control systems. Commissioning over a period of months and subsequent purchase of spares will further increase costs. Large areas will have to be cleared not only for the works, but also for the clay pit. The process itself and the transport of raw materials and products can prove a nuisance. Production of many millions of bricks per year necessitates the finding of sufficient markets, and involves the use of fuel for getting bricks to the building sites. Feasibility studies for large-scale plants commonly assume several shifts being worked per day for nearly all the days of the year. Such plants are not adaptable to variations in market demand. There is no allowance for workers’ absenteeism (e.g. during the agricultural season), neither do they usually take into account the difficulty of obtaining spare parts from overseas in the event of a breakdown. If the latter does occur, the whole production ceases. These large plants require electric power and high grades of fuel for the kilns.

In those situations where a large plant may be considered, it would be normal to conduct a full feasibility study, examining raw material quality and reserves for the expected life of the works (e.g. 50 years), and a thorough market survey. A specialist consultant would be required for such a feasibility study.

V. Content of the memorandum

The following eight chapters of this memorandum deal with the technical aspects of brick manufacturing. Chapter II describes various raw materials entering in the production of bricks while Chapters III to IX describe the various production processes in the following order:

Chapter III

Quarrying (methods and equipment)

Chapter IV

Preprocessing (grinding, sieving, wetting, etc.)

Chapter V

Forming (equipment, skill requirements, etc.)

Chapter VI

Drying (natural and artificial, drying shrinkage, etc.)

Chapter VII

Firing (kiln types, fuels, etc.)

Chapter VIII

Mortars and renderings (purpose, types, etc.)

Chapter IX

Organisation of production (plant layout, water and fuel supplies, labour, etc.)

Technical details on each subprocess are provided, including advice for improving product quality, saving fuel, increasing labour productivity, minimising losses, etc.

Chapter X outlines a methodological framework for estimating unit production costs associated with alternative production techniques. An illustrative example is provided with a view to showing how this framework may be applied to a specific bricks production unit. Finally, Chapter XI analyses the various socio-economic effects of alternative production techniques, including employment generation, foreign exchange savings, fuel utilisation, etc. The memorandum concludes with the following appendices: Glossary of technical terms, bibliography, list of institutions concerned with brickmaking, and list of equipment suppliers.

Note:

1 The references are to entries in the bibliography (Appendix II).

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