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 considerable value to these economic 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 natural deposits of sand that is suitable for producing concrete tiles. These sands will contain a balanced distribution of course and fine particles ranging from 4 mm downwards.The coarse particles provide strength and the fine particles 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. Ordinary Portland Cement (surface area 350 sqm/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 of 450 sqm/kg) is advisable.
In order to simulate the vibrant colours of ceramics or naturally occurring stone, the grey of concrete is artificially altered by the addition of coloured pigments (synthetic iron oxides). As these pigments colour only the cement, the level of addition is normally calculated on the cement weight. The pigment is added as a dry powder or as a liquid and, depending on the required colour, 2.5 – 5% is the generally accepted proportion.