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close this bookJournal of the Network of African Countries on Local Building Materials and Technologies - Volume 1, Number 3 (HABITAT, 1991, 46 p.)
View the document(introduction...)
View the documentForeword
View the documentThe role of a Network in strengthening local technological capacity in the production of Building Materials
View the documentMalawi: Production process, application and acceptance of fibre concrete roofing products*
View the documentNigeria: Natural-fibre Shwishcrete technology for low-cost roofs*
View the documentNigeria: Appraisal of coir-fibre cement-mortar composite for low-cost roofing purposes*
View the documentMalawi: Improved concrete roof tiles and roof-tile machines*
View the documentEast African roof thatching techniques being tested in India*
View the documentCorrugated roofing sheets from coir-waste or wood-wool and Portland cement*
View the documentPublications review
View the documentEvents
View the documentBack Cover

Malawi: Production process, application and acceptance of fibre concrete roofing products*

* Submitted by J.K. Kateregga, Chief Technical Advisor, Rural Housing Programme UNCHS (Habitat).

Figures by: Uffe Leinum and J.K. Kateregga.

A. Background

In recent years, considerable research has been carried out on fibre-cement roofing (FCR) technology (sheets and tiles) and most of this work has been published by organizations such as the Swiss Centre for Appropriate Technology (SKAT), Intermediate Technology Workshop (ITW) and the United Nations Centre for Human Settlements (Habitat). These organizations are in the forefront of collecting and disseminating information from different sources all over the world, as a means of promoting the production and application of those FCR products in low-cost construction projects.

The Rural Housing Programme (RHP) in Malawi is probably one which has the longest and most extensive practical experience in the development, production and application of FCR products. This has been judged through the statistical data collected by SKAT from more than 25 countries all over the world in 1985-1986. By that time, RHP had over five years of practical experience in this technology and had made many improvements in the production, application and quality control of FCR products. It had established three regional and 24 district housing centres all over the country (see figure 1) where more than 200 local builders and artisans had been trained in the production and application of these products in housing construction. Since then the technology has continued to become popular and has even penetrated in the urban housing areas as reflected in section E of this article.

B. Production process and quality control of roofing sheets and tiles

Initially, RHP developed and produced FCR sheets. These activities were carried on until 1984, when RHP started developing smaller and lighter FCR sheets (tiles). By the end of 1987 the development of roofing tiles had also been completed and tested to the final stage including preparation of technical specifications and production equipment. The two products (sheets and tiles) have very much in common, that is why they are treated together in this section. They differ mainly in size and shape and production equipment as reflected in sections C and D below.


Figure 1. Malawi, location of the Rural Housing Programme's regional and district centres

The raw materials for FCR products are:

(a) Fresh (without lumps) ordinary Portland cement;
(b) Clean river sand - sieved through 2mm sieve;
(c) Clean dry chopped sisal fibre with a length of not more than 20mm;
(d) Clean water.


Figure

Based on the specifications of the mix design already established (contained in section C below), raw materials are batched to the correct quantities and mixed together when dry. Water is then added gradually until workability is achieved. It is essential to have the production process and initial 24 hours curing under a shed with sufficient protection from direct sunshine, wind and moisture.


Figure

Experience has shown that for the tiles, the amount of fibre is not essential, since they have very shallow valleys and therefore do not form deep cracks when moulding is taking place.

Once the mortar is ready, it should be used quickly (within 30 minutes) and before it hardens. Mortar is batched in the correct quantities for the sheets or tiles and placed on a table board covered with polythene paper for the sheets, or a tile vibrator board for the tiles. The mortar is spread evenly all over the board within the frame for the sheets and tiles respectively. The table board for sheets can either be vibrated or tamped to achieve the required compaction before moulding takes place. For the tiles, a manually-operated vibrator is used to achieve the required compaction of the mortar on the table.


Figure


Figure

The sheet is moulded into a concrete mould having corrugations of standard asbestos sheets and cut in 1000mm long and 800mm wide, while the tiles are moulded on shallow-valley tile moulds. Hoop wires are inserted in the correct places for fixing sheets or tiles on to the purlines of the roof structure. The fresh sheets/tiles are placed under a shed to undergo the first curing stage of 24 hours setting. They are demoulded after 24 hours and placed under water for the 7 days of curing period. After the 7 days of curing in water, the sheets/tiles are taken out for curing in the open air for 21 more days, making a total of 28 days, after which they are ready for transporting and installation on the roof.

For good quality products, use of good raw materials and tools is essential. Accurate batching of raw material, thorough mixing, sufficient compaction and proper curing must be strictly followed. The products should also be randomly tested for transversal strength, impact resistance, resistance for water absorption and possible cracks, before they are installed on the roof. Furthermore, the roof structure must be properly constructed with correct pitches of more than 22.5 degrees for sheets and 25 degrees for tiles. The purlines must be properly and adequately supported and must be straight and of correct size to cover a given span without deflecting after carrying the weight of the sheets/tiles.

C. Established specifications of performance standards

As mentioned in section B above, there, are many similarities in the technical specifications for the production and curing process of roofing sheets and tiles and these are summarized below including sand size particles, cement/sand mix ratios, water/cement ratio, curing stages etc.

D. Production equipment for roofing sheets and tiles

The production equipment for roofing sheets is a simple wooden table as shown in the following figures and can easily be produced by a good carpenter with simple tools. Currently, all these tables are made by small-scale carpenter contractors in the field to meet the requirements of over 80 sheet-making contractors having an average of two such tables each. The tables are also easy to maintain by the same contractors in the field.

There are two types of these tables, one which produces compaction by tamping the fresh mortar on the board using a timber plank and the second which hits the board from underneath to produce some vibration/compaction of the mortar. Although the table, producing compaction by vibration is more efficient, it requires more frequent maintenance and, as such, most contractors prefer the table with the tamping stick. The production cost of each of these tables with all required ancillaries is currently about MK250 (about $US100).

Summary specifications for roofing sheets and tiles

Item/specification

Roofing sheet

Roofing tile

1. Cement/sand mix ratio by volume

1:2

1:2

2. Type of cement - ordinary Portland

less than 12 weeks/fresh

12 weeks/fresh

3. Sand type and maximum size

2mm river sand

2mm river sand

4. Water/cement ratio by weight

less than 1:2 or 50 per cent

1:2 or 50 per cent

5. Minimum curing period

28 days

28 days

6. Number of pieces produced from one cement bag (50 kgs)

8 sheets

65 tiles

7. Size (length × width × thickness)

1000 × 760 × 9±l

600 × 280 × 7 ± 1

8. Overlap along slope of pitch of roof

150mm

75mm

9. Minimum and average angle pitch of

22.5° and 25°

25° and 27°

10. Average sizes of purlins (diameter), for span of 3m

85mm

60mm

11. Spacing of purlins

850mm

525mm

12. Weight per unit

18.5 ± 2 kg

2.6 ± 0.3 kg

13. Effective covering area per piece

0.62m2

0.13 m2

14. Number of pieces per m2

1.6 sheets

7.7 tiles

15. Weight of pieces per m2

30 ± 3 kg

20 ± 2 kg

16. Current average production rate/day (Dec 1990)

40 sheets

200 tiles

17. Average roof area coverage/day/gang of 3

20.1m2

16.7 m2

18. Minimum transverse/load breaking strength (28 days old)

140 kg

40 kg

19. Water absorption after 28 days curing

0.69

0.54

20. Permeability after 28 days curing (2 hr rain)

No dampness

No dampness

21. Resistance to heat transmission insulation value

High

Medium

22. Resistance to impact force/damage

High

Medium

23. Resistance to brittleness/damage

High

Medium

24. Resistance to wind uplift forces

High

High

25. Level of wastage/damage during handling units

3 ± 1 per cent

10 ± 4 per cent

26. Cost per unit, i.e., selling price

K5.85

K1.00

27. Cost of units per m2 area

K9.40

K7.70

28. Cost of GCI sheets gauge 28 per m2

K33

-

Note: The above specifications were established by RHP in cooperation with the Polytechnic University of Malawi and the Malawi Bureau of Standards through intensive research and tests to achieve the minimum performance standards required for roof covering in tropical areas.


Figure 2. Table for producing roof sheets


Figure 3. Hand-operated tile vibrator


Figure 4. Improved roofing-sheet tamping table

The equipment for producing the tiles is a small metal tile vibrator. It was initially developed by ITDG in the United Kingdom, but RHP made some modifications to make it more ideal for rural conditions. The ITDG tile vibrator uses power either from the mains or from a car battery which are not readily available in the rural areas. The RHP modified tile vibrator is hand-operated to produce the vibration.

In spite of the modifications made, the machine has remained unpopular in the rural areas due to the fact that:

(a) It has metallic structure which can only be manufactured and maintained in urban areas where there are metal welding workshops with good skilled welders.

(b) It is far more costly than the wooden table for sheet making both for its initial capital cost and for maintaining it. Currently it is costing over MK 1000 (over $US400) which is four times more costly than the cost of the wooden table. As a result, the tile vibrator and the roofing tiles have not been as popular as the roofing sheets in the rural areas in Malawi although in urban areas they have picked up very well.


Figure 5. Details of moulding process for sheets

E. Application and acceptance of roofing sheets and tiles

The FCR sheets have been applied by RHP since 1981, initially on an experimental/demonstration basis up to 1984. In 1985, when the Rural Housing Credit Scheme was introduced to provide villagers with loans to improve their houses, the demand for FCR sheets went up because they were the most economic and cost-effective available roofing materials produced in the rural areas country-wide. By the end of the experimental stage in 1984, only about 5800 sheets had been produced in all the three regional centres and the six district centres in operation by then. These had been used to roof staff houses, workshops etc. at these centres on an experimental/demonstration basis.

From 1985 onwards the production had to be stepped up to meet the increasing demand and, as such, a scheme of small-scale contractors in sheet making had to be introduced in 1986.

This increased the output from just 10 sheets per day's production per centre to over 50 sheets. The number of sheet- making contractors also rose very rapidly from none in 1986 to over 70 by June 1990 of whom 25 arc women sheet-making contractors who are doing very well. The average total production per day in all the three regional, 24 district centres and eight subcentres is over 1500 sheets or over 33,000 sheets per month (22 working days). This is enough to roof over 330 beneficiaries' houses per month or 3900 houses in a year. The current capacity of roofing sheets output is sufficient to meet the RHP annual target figure of 2000 beneficiaries and to meet the expected demand from independent/private house developers and other users whose demand is also rising very rapidly.

On the side of the roofing tiles, their application has not picked up very well in the rural areas mainly because of the limiting factors outlined in section D above. By the end of 1986, over 4000 tiles had been produced at the three regional centres where the tile vibrators were being provided by RHP for training tile makers. The position did not change much especially in the rural district housing centres, despite the fact that many families' existing houses required light-weight roofing tiles to roof them. This means that the metal tile equipment is a major limiting factor which needs to be made simpler and out of timber, so that it can easily be produced and maintained by the carpenter/joinery contractors in rural areas.


Figure 6. Mitring of sheets and fixing details


Figure 7. Fixing details for roofing sheets


Figure


Figure


Figure 8. Layout for fixing roof sheets

The situation in urban areas is much better for both the roofing sheets and tiles. Since 1987, the Malawi Housing Corporation and Habitat for Humanity (a non-governmental organization) operating in urban areas took a positive stand by applying these low-cost roofing materials in their low-income high-density urban housing schemes. This was immediately after the declaration of the Malawi Bureau of Standards approving the materials as meeting the minimum standards for roofing in urban high-density housing areas. Today, Malawi Housing Corporation has a World Bank-funded low-income housing scheme of 2000 housing units in the three cities of Blantyre, Lilongwe and Mzuzu. These houses are now under construction and they are being roofed using FCR sheets for 1000 units and FCR tiles for another 1000. The production of both roofing sheets and tiles is going on well at the sites and, in Lilongwe alone, over 200 houses have already been roofed, half the number with the roofing sheets and the other half with the roofing tiles. This means that over 10,000 roofing sheets and over 50,000 roofing tiles have been produced and used at that site alone. The situation is even better in Blantyre where the scheme started and where the largest number of housing units are being built.

This is justified proof showing that the FCR products have been fully developed and accepted as roofing materials in both the urban and rural low-income housing schemes. They have proved to be quite cost effective when compared with the cost of the conventional GCI sheets in Malawi. There is a cost reduction/saving of at least 40 per cent when FCR products are used instead of GCI sheets of gauge 28. They also have other advantages, including their coolness during hot seasons and quietness when it is raining. They have become very popular for roofing schools and churches too. They are easy to produce on site by less skilled local people and, therefore, more easily available in both rural and urban areas where production workshops have been established.


Figure 9. Position of overlaps

The level of production and application of FCR products has reached an advanced, full-scale, sustainable stage in Malawi. Both the products and the required equipment are being produced in sufficient quantity to meet the increasing demand in the country. Furthermore, considerable employment has been generated in the production workshops and for the installation works at the sites. RHP alone has over 100 contractors who have employed on average eight workers (sheet/tile makers) each in their workshops. The number could be almost the same in the urban areas or even more, as, the urban low-income housing production is faster than that in the rural areas.


Figure 10. Typical areas relating to quality control

F. Conclusion

The preference of one product over the other (roofing sheet or tiles) has not been found significant in Malawi because comparative analysis has shown that both products have more or less equal advantages and disadvantages although not the same. For example, while the sheet is commonly criticized for its heavy weight which is 30 per cent more than the weight of the number of tiles equivalent to the one sheet roof covering area (4.77 tiles), the light-weight tile is disadvantaged by being more brittle and easily blown off a roof by strong winds.

As to cost difference, one sheet costs MK5.85 but the cost of the tiles of the equivalent roof coverage area is MK4.77 which is 81.5 per cent the cost of the roofing sheet. When one takes into account the high cost of the tile equipment and the more timber needed for the tile-roof structure compared with the sheet, plus a more skilled carpenter to install the tiles, the above apparent difference in cost may not be substantial anymore. Thus, the Rural Housing Programme policy approach in Malawi is to fully introduce and promote the two low-cost roofing materials as alternatives to the more costly conventional roofing materials in the country and let the users make their choice between these two materials. It is not appropriate to promote one of these two materials against the other, they are both good alternatives and not one being a substitute for the other. That is why in the case of the Malawi Housing Corporation urban low-income housing scheme funded by the World Bank, there are equal numbers of housing units roofed by each of these two roofing materials.


Figure 11. Testing of roofing sheets and tiles


Figure 12. Typical roof structure and fixing details for roofing sheets and tiles