Micro concrete roofing tiles
Practical Action
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 needed, but
some additional sheets should be kept in stock to replace those which wear out.
Accurate batching of sand and cement is essential. For this reason, it is usual to have two
batching boxes to measure out exactly the right amount of sand and cement needed for one
tile. A measuring jug for water, to ensure that similar amounts of water are added for each
tile, would also be useful.
A water tank is needed for curing the tiles. As the tiles are cured in warm water for at least
five days, the tank should be large enough to hold 1000 or more tiles. A single tank to
accommodate this number of tiles would need to be about 8 metres long, 0.8 metres wide
and at least 0.6 metres high, although it probably would be more convenient to use a number
of smaller tanks.
The materials needed to make MCR tiles are:
sand
cement (Ordinary Portland Cement)
water
pigments (optional)
The need for sand with a suitable grading has already been noted. More specifically, the
following guidelines are used for sand grading for MCR tiles.
Tile thickness
maximum grain size
above 2mm
0.5 to 2mm
below 0.5mm
6mm
4mm
25-45%
20-50%
15-45%
8mm
5.5mm
30-50%
15-40%
15-45%
10mm
7mm
35-55%
15-40%
15-45%
In addition, the clay and silt content should be less than 4% in all cases. A set of three sieves
with openings of approximately the sizes indicated above would be a very useful acquisition
for the serious MCR tile producer. These could be used for determining the sand size grading
and, possibly, for making sand heaps of
different sand sizes, which could
afterwards be mixed in appropriate
proportions. A clean sharp sand is the
best to use.
The water used should be clean and
free from significant quantities of
dissolved salts, particularly sulphates.
If water of good enough quality to drink
is available, then this should be used.
Pigments for colouring the tiles are
popular in some areas. Red is probably
the most common colour used for tiles.
Figure 3: Smooth under vibration
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