|FCR: Fibre Concrete Roofing (SKAT, 1987, 185 p.)|
|1. Limits of application and acceptance|
FCR is a material that does present technical problems, mainly when made in the form of sheets, and social factors determine whether those problems are being resolved quickly or whether they are allowed to develop into big problems.
Generally the experiences are positive where the owners of the roof had something to do with the decision and the manufacture of the material, as well as the installation, and where the form of payment of the houses is clear. Often pretexts are sought to not pay for houses in government or NGO sponsored projects and minimal problems In the roof construction are exaggerated for this reason.
In public buildings, experiences range from total success all the way to total failure, often for social reasons such as maintenance or a resentment because the government or NGO did not provide a more prestigious material. Again, if the users made a conscious decision to use FCR the chances for success are far greater.
Often projects which use FCR are termed a success by some visitors and failure by others. This very often simply reflects the reaction of users, who are more or less identified with the product. For example during a meeting with the future inhabitants of a housing colony the people complained about the deficient roofing material, but a workman, who didnt have a house yet, asked permission to use the moulds to make some sheets for himself.
Not only direct physical involvement can bring about an identification. Probably even more important is the fact that the people have consciously taken the decision to use FCR, and this criteria basically applies to any material. Ifthe choke of the roofing material is sound, and In a guided project it should be, then the users can and must be Included In that decision.
Often we find that less than- perfect roofs are accepted and even defended by the owners If they feel that the work and the choice was really theirs, whereas practically perfect roofs sometimes a rejected in order to gain some social or economic pay-off if the beneficiaries do not have a real identification with the project.
Only those purely social factors explain why one group happily repairs the leaks in the roofs and meets repayments on the house, while another group nearby uses any defects in the roofs to justify their not paying their quotas Even after this latter group received new corrugated zinc roofs they still found another reason to not pay their quotas.
Projects where FCR is imposed for financial or philosophical reasons (Appropriate Technology) by the leadership will seldom work.
Care should be taken to not disrupt or endanger the trade of
other local producers of existing
appropiate roofing materials such as clay tiles.
It was about 1980 when the news about FCR started to spread and in many countries interested people began to experiment or called upon others for training.
A wide variety of procedures were invented and subsequently modified, a great deal of resources and time were spent, and often poor quality products were placed on roofs. But there are also several well-documented experiences which testify to the real possibilities for FCR.
Unfortunately, among those technicians and project directors interested in appropriate technology, many are very doctrinal and often apply manuals and instruction papers without adequate practical experience and, thereby, cause much damage.
If a variety of roofing materials is freely available and the cost is not a direct and immediate concern of the users (aid programs etc) they will rarely make a deliberate choice to adopt FCR. However, FCR can compete in many markets because of its price or where other materials are scarce. Again, tiles seem superior to large sheets, for their appearance, uniformity and tradition.
In relation to organic (thatch) roofing materials, FCR Is more durable, more wholesome as it does not attract insects, mice and rats, minimizes fire hazards, and usually is preferred for its appearance. But it has several negative factors because of foreign exchange element, technical dependence and usually higher cash cost.
FCR when compared with galvanized corrugated Iron sheets, Is usually cheaper, better for physiological reasons and has a relatively low foreign exchange content, but usually the public prefers metal sheeting if given the choice. Durability depends upon the gauge and quality of the corrugated iron.
Compared with asbestos cement, FCR usually is cheaper and because transport problems to the rural area can be avoided by production on-site, less foreign exchange is needed. But asbestos sheets are more certain to be durable, easier to handle and have more resistance to cracking.
Clay tiles need a much stronger wooden structure than FCR and they often are of poor quality. But usually they are cheaper, use less (almost nil) foreign exchange and are physiologically better, more durable and more aesthetically pleasing.
While the large sheets have the appearance of asbestos cement and therefore get treated as such, or, even worse, are treated like metal-sheeting, the FCR tiles are compared to clay tiles and, therefore, they receive more careful handling.
Nobody will try to walk on tiles, but one expects to be able to walk on a sheet, at least along the purling.
It is known that tiles crack if one throws stones at them and baseball is never played near tile roofs. But all those precautions which are inherent in many societies do not apply for FCR sheets, so the sheets often are subjected to much more wear and tear than the tiles.
FCR sheets are far more rigid and fragile than most other types of roofing sheets and probably this is their greatest drawback, as the sheets are often treated Incorrectly.
Tiles have the advantage of being compared to and treated like traditional clay tiles and, therefore, can more easily fulfil or even surpass expectations. Because the stress within the tiles is smaller than in the sheets, tiles are less susceptible to cracking.
Mechanical damage Is the main problem affecting FCR products. It is often a deficient roof structure that causes cracking, through warping or bending of wood.
But also vandalism (stone-throwing) and baseball have caused much damage. Moreover, from Bangladesh there is a report that a hailstorm, with hailstones as big as fists caused severe damage. There has been no damage reported which seems to indicate deterioration of the sheets either through Influence of weathering, sun or other rays, heat, cold or ageing.
Some eight years of practical experience reveal that life expectancy may be high If no mechanical damage occurs from causes such as those discussed above. Repairs to minor cracks can be done by painting them from the inside with white glue or even oil paint. Larger forms of damage require that the sheet be changed and it has been discovered that, in order to do this, the remaining sheets have to be removed. If the sheets were nailed to the wooden Structure, heavy losses will occur, but if they have been fixed with wire loops or J-hooks only a few sheets should be damaged in this procedure. Again, the tiles are much easier to handle and breakage is minimal.
While it seems unwise to produce FCR sheets for the free market, the sheets are widely used in development projects because of their low production cost. However, where the construction material market is tight and the public possesses the means to purchase, the technique will spread to supply the free market. Such has been the case In Nicaragua, which situation has resulted in extreme differences in quality from one producer to another.
The use of tiles instead of large sheets appears to ease that situation, as the technique is more uniform and the possibilities for error much smaller. In Africa there exist several successful tile businesses that do compete on the free market. The cost advantage of FCR tiles over Gil sheets is primarily obvious for for small buildings with spans of up to 7.5 m. In Nepal, a 4m x 7m FCR roof costs 40 % less than a corrugated iron sheet roof. The reducing cost advantage for spans over 7.5 m is due to the closer spacing of rafters and the extra structures needed.
While breakage of sheets in transport according to the questionnaires does not seem to be a large problem ( 1 to 5 % breakage) it is established that in certain cases this figure may be much higher.
It can be said, that It depends almost totally on the driver of the vehicle, whether it be a truck or an oxcart, and certain precautions taken, like stacking the sheets vertically and with some soft packing material (grass, husk, old tires etc). There are many reports where no breakage occurred, but only If the driver is interested in his load, or if the owner is directly involved in the transport. The same holds true in most cases for asbestos cement sheets, though to a lesser degree.
FCR is a real alternative to other roofing materials, with its limitations like any other material and should be used selectively. Generally, FCR is more suitable to small roofs and it is more difficult to use it on large structures because of the roof pitch necessary.
Also, the social integration of the community can place limitations and where vandalism is common, FCR might not be suitable.
Tiles are usually a better choice than large sheets, but there are places where sheets are better suited, mainly when the production facilities are adverse and the battery powered vibration table can be a problem because of the lack of electricity. In the near future hand operated vibrating tables for tile production will be available. By then the tiles will be the better choice in almost all cases.
Great care should be taken before embarking on a sheet production. Training and follow-up assistance have to be more extensive for sheets than for tiles.
Often, it is a deficient roof structure or social problems (including carelessness) which cause the cracks which determine the life span of a roofing sheet.