The basic raw materials used in the manufacture of coloured concrete roof tiles are sand (quarried or river), cement, colour pigment and water. The production of concrete roof tiles adds high value to these economical and readily available materials and as a result, the popularity of the product continues to grow in both established and developing countries alike.
Most countries are fortunate in that they have ample deposits of sand that is suitable for producing concrete tiles. These sands will contain a balanced distribution of coarse and fine particles ranging from 4mm downwards. The coarse particles provide strength and the fine particles provide a close, textured surface finish. Where natural sand deposits are rare, crushed aggregates will provide a suitable substitute and make an equally good tile.
The grain sizes of sand can be checked by separating a sample through a series of vibrating sieves and comparing the results with a classification chart showing the ideal particle grading.
Click on the classification chart above to see the ideal particle grading
Ordinary Portland cement (surface area 350m2/kg) is most widely available and recommended for general use in the roof tile industry. When a reduced curing period is required, the use of a rapid hardening cement (with an increased surface area of 450m2/kg) is advisable.
PFA (Pulverised Fly Ash / Fuel Ash) may be blended with ordinary Portland cement to produce a less expensive material, Portland PFA cement. Similarly, GGBS (Ground Granulated Blast furnace Slag) blended with ordinary Portland cement, produces slag cement, and either of these blended cements can have advantages in the production of concrete roof tiles.
In order to simulate the vibrant colours of ceramics or natural stone, the grey of concrete is artificially altered by the addition of colour pigments (synthetic iron oxides). As these pigments colour only the cement, the quantities added are normally calculated on cement weight. The pigment is added as a dry powder or as a liquid and, depending on the colour desired, between 2.5% and 5% is the generally accepted proportion.