Tinting strength of pigments
One brand of pigment is not the same as another. Two pigments identical in appearance may have a completely different yield. The decisive property in the use of a pigment for colouring concrete is tinting strength, which determines the depth of colour for various brands of pigment. A sample mix prepared under practical conditions can provide reliable information on this.
Natural colour of the cement and colour effect
In colouring concrete it is not the aggregate that is pigmented, rather the cement paste is coloured, which then forms a layer on the individual aggregate particles. Therefore the more the coloured cement paste is diluted with aggregate, the less intense will be the colour of the concrete.
Grey has a subduing effect on all colours, no matter where they are. Therefore, it is not possible to colour concrete made with normal grey cement as brightly as concrete containing white cement.
The gain in colour purity obtained by using white cement depends, however, on which pigment is added. In the case of black there is virtually no difference between concrete made of white cement and one made of grey cement. With dark brown, red and burnt umber the difference is small while it is considerable with yellow, marigold, green and blue.
Pigment loading and colour effect
With increasing pigment loading, the colour intensity moves towards saturation point. Adding more pigment at this point does not significantly deepen the shade and may affect the structural strength of the concrete.
The saturation point lies between approximately 5% – 8% calculated on the weight of the cement in the mix. However a good depth of colour can be achieved at 4% loading with our Oxides.
The normal ready mix concrete strength is 6 x 40kg bags of cement per cubic metre of concrete. 4% of this equates to approximately 9kg of oxide. Mortar on the other hand with its higher cement content requires more pigment. It is important to remember that pigment addition relates to the amount of cement in the mix and nothing else. A rough guide is to use approximately 1.5kg of oxide per 40kg bag of cement.