Micro-Concrete Roofing Tile
Production
Much attention has been paid to developing the small-scale production of concrete roofing
tiles as an affordable alternative to both traditional roofing materials, such as thatch, and
modern, mass-produced, often inappropriate, galvanized iron sheeting or asbestos cement.
These tiles are relatively low in cost, durable (with a life span expected to exceed 20 years in
most areas), aesthetically acceptable, able to offer adequate security and comfort, and
provide protection from both the heavy rain and the hot sun.
Concrete roofing tiles are now produced by small businesses in a number of countries in
Africa, South and Central America, Asia and South-east Asia, and in the former Soviet Union.
The key to the success of this technology was the development of equipment and techniques
to produce the tiles on a small scale. It typically costs US$5000 (excluding land and
buildings) to set up a concrete roofing tile workshop, and can be less than US$1000 in areas
where the vibration equipment and the moulds are made locally.
When the technology was first developed it was decided to make large roofing sheets similar
in size and shape to the corrugated asbestos or galvanized iron sheets used on many
buildings. These were reinforced with natural fibres such as sisal or coir. The fibre-cement
mortar mix was simply spread out by hand on a flexible plastic sheet in a large mould.
Afterwards the sides of the mould were taken away and the sheet with the mortar on top was
gently pulled over onto a corrugated mould where it took its shape.
Problems were experienced with decay of the fibres and cracking of the sheets after only a
few years, and so the production of fibre-reinforced concrete roofing sheets has been
abandoned in many countries.
The next development was production of fibre-reinforced concrete roofing (FCR) tiles. With
tiles (typically about 500 x 250 x 6 or 8mm) the performance of the fibre is less critical than
with sheets. The fibres are added largely to control damage caused by impact during
handling. Once placed on the roof, tiles are unlikely to crack if the fibres decay. In addition,
FCR tiles are vibrated during their production which gives them added strength and durability.
It has also been found possible to make fibre-reinforced semi-sheets (of size 600 x 600 x
8mm) by the same method without any adverse effects.
A more recent development has been to make concrete tiles without any fibre at all. These
are the so-called micro-concrete roofing (MCR) tiles. Greater care needs to be taken with
MCR tile production compared with FCR if the number of damaged or sub-standard tiles is to
be kept low. MCR tiles are also more brittle than FCR tiles, and can be damaged if dropped
or handled carelessly when transporting them or fixing them to the roof.
Quality control
To produce a good MCR tile, care needs to be taken in the quality of the sand to make the
mortar. This should have a regular grain-size grading – without too much material of one size
and, particularly, without too much fine silty material. If the sand from one source contains
too much material of any one size it should be mixed with a sand of different grading from
another source. In addition, the batching of the quantities of sand, cement, and water needs
to be done accurately – to ensure that there is enough cement and that the mix is not too wet.
The tilemaker needs to mould the tile with care and skill, and it is important that the tiles are
properly cured.
With FCR tile production there is some capacity for these quality aspects to be less rigorously
exercised, but with MCR production there is no margin to be lax on quality control if large
numbers of damaged or sub-standard tiles are not to result. If the potential producer cannot
ensure good quality control at all stages of production, then it probably is not a good idea to
Micro concrete roofing tiles Intermediate Technology Development Group
produce MCR tiles.
Equipment and materials
The equipment and materials needed to produce MCR tiles are the same as for FCR tiles,
except that no fibre is used and the sand used needs to be of good quality, as noted above.
The essential equipment is:
• a tile vibrator
• moulds
• plastic sheets
• batching boxes
• a water curing tank
• a table to work on
The use of a vibrator is essential for
MCR tile production. Vibration
helps to consolidate the mortar mix
and removes air bubbles, which
would otherwise cause weak spots
in the hardened tile. The vibrator
unit itself consists of a flat metal
plate which is suspended on
dampers and to which is attached a
rotating eccentric cam. It is the
rotation of this cam which translates
into the up-and-down motion of the Figure 1: Place the polythene interface sheet
plate. A hinged metal cover fits
onto the plate. This defines the
sides of the tile. The vibrator may be driven manually, electrically with a standard 12-volt
truck battery, or on mains electricity.
Because cement mortar sets slowly and the tiles need to be left on the moulds at least
overnight before they can be removed, the producer will need enough moulds to cover a
whole days’ production. A single person should comfortably be able to make at least 200
tiles per day, and probably considerably more. (Note: the cost of 200, or more, moulds
should not be underestimated – they could cost more in total than the vibrating unit itself.)
Because it is important that MCR tiles cure in a damp environment, the enveloping type of
mould needs to be used. These moulds
are stacked one on top of the other and
hence cover the curing tiles and prevent
them drying out too quickly. Although
cheap concrete moulds have been used for
FCR tiles, which then cure open to the air,
more rigorous standards are needed to
cure MCR tiles. The stack-up type of
moulds are made of plastic. Note also that
out of a batch of 200 moulds, at least 10
should be ridge moulds for making the
specially shaped tiles for the ridge of the
roof.
Tiles are moulded on top of a plastic sheet
on the tile vibrator. After vibration, the tile
is removed carefully from the vibrator, still
on its plastic sheet, and positioned on the
mould which forms its shape. The same
number of plastic sheets as moulds will be Figure 2: Work the mortar mix under vibration
needed, but some additional sheets should
be kept in stock to replace those which
wear out.
