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Colour

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.

Blending of Oxides for Different Colour Shades

Oxides, like paints, can be mixed to provide a variety of colours, as seen in the photos throughout this website. We can supply ‘shot blends’, i.e. small pre-mixed blends of oxides to mortar and plaster contractors to standardise colours and eliminate the often difficult task of preparing blends on site.

 

The advantages of measured quantities of oxides

We can supply measured quantities of our Oxides to the readymix concrete industry in 20 litre plastic buckets. This applies to standard grades, G & C grades or blends. The advantage of the G & C grades is that they flow when being administered, causing less dust nuisance. There is also no need for plant staff to measure out quantities for dosage as this has been calculated by us once the load sizes have been advised.

 

Using pigments

When mixing coloured concrete onsite, ingredients must be placed into the mixer in sequence to ensure the pigments disperse fully.  With powdered colours, put pigments into the mixer along with aggregates and approximately half the required water and mix well to ensure a uniform blend: follow this by adding cement and sufficient water to obtain the desired consistency.

Application

Water addition and strength of concrete

Darker, less bright colours will be obtained with concrete of lower water/cement ratio that has been compacted by compression than concrete of higher water/cement ratio such as vibrated concrete.

The lower the water/cement ratio of a concrete, the greater its strength, providing the concrete is not very dry making it unworkable.
Also as the water/cement ratio increases, so the shade of the concrete where pigment has been added becomes lighter. It is important then to maintain a consistent water/cement ratio.

 

Fading of coloured concrete

Chemical reactions within concrete itself can reduce colour brightness. It is also important that the concrete is not allowed to dry too quickly. As the concrete cures, especially in hot summer weather, slow the hardening process down by keeping water on the surface. The inorganic pigments supplied by Bayer are manufactured for optimum resistance to the weathering effects of nature and will retain good colour stability during the normal life of concrete products that the pigments are used in.

 

Patchy finish

This effect occurs more frequently in outdoor locations however concrete is a natural material and subject to mottling and colour variations whether pigmented or not.  The causes have not been proven however it is suspected that variations in ground moisture under the concrete, partial shading of worksite and or weather variations during the pour/curing may affect the appearance.

It is essential to ensure consistency in the concrete batches, minimise added water at site, use a light powered float for consistent density and finish, keep concrete wet to cure for a week.

 

Efflorescence

Efflorescence is the result of free lime formed when the cement sets and migrates to the surface of the concrete where it reacts with the carbon dioxide in the air to form insoluble calcium carbonate.  This has a white powdery appearance.

Efflorescence will disappear in the course of time, normally 18 months to two years of natural weathering however this depends on the climatic conditions and on the amount of traffic the concrete has to bear.

If this natural process takes too long, the efflorescene can be treating with dilute acid in the following way:-
Soak the concrete surface thoroughly with water and then spray with a diluted acid solution (e.g. diluted Spirits of Salts – 1 part Spirits of Salts to 3 parts water). Use a common garden spray pump and wear protective clothes, acid-resistant shoes, protective gloves and safety goggles. Apply the treatment carefully to avoid a spotty result. Gently scrub with a soft broom during treatment to ensure good penetration and uniform coverage. After a short time rinse the concrete thoroughly with flowing water.

 

Grout bleed

Please note that floors which are tile cut for grouting should be sealed with concrete sealer before grouting to prevent grout bleed into the coloured concrete.

For the perfect
concrete finish,
choose Oxco.

For the perfect
concrete finish,
choose Oxco.

Contact us

  • Oxide Distributing Co Ltd

  • info@oxco.co
    09 444 9331

  • 10 Robertson St, Westport 7825.
    40 Whiore Avenue, Tauriko, Tauranga 3110.
    Australia: NSW & WA