Technical Application Information: Coloured Exposed Concrete

Technical information on incorporating the concrete colour into the tender specifications

Basics

For the production of coloured exposed reinforced concrete, only pigments may be used which are generally suitable for colouring cement- and lime-bound building materials and which also meet the additional requirements for use in reinforced concrete.
Accordingly, these pigments and pigment preparations must comply with DIN EN 12878, Category B.
In principle, selected powder pigments, liquid paint designated F-BB (liquid paint for reinforced concrete) and certain pigment granulates may be used. For further details, please refer to our two Technical Application Information, ‘Precast Concrete Elements II’ and ‘Ready-mixed Concrete II’.

Usage

Typical dosage levels are approximately 2-5% of pigment based on binder content. There is no downward limit. Pigment amounts below 1% are also often used, particularly in conjunction with light-colored binders, to produce pastel shades. There is probably an upper limit: In accordance with DIN EN 12878 specified above, no more than 10% pigment should be added to the concrete. Since saturation usually occurs at lower doses (7%-9%), this limit is not exceeded. In the case of liquid paint, when calculating the dosing height, it should be taken into account that a significant mass fraction of the liquid color is water. For example, the pigment content of red iron oxide liquid paints is generally 50%. The amount of liquid color to be added is therefore twice as high as the desired amount of pigment: For example, if you want to color concrete with 4% iron oxide red Bayferrox® 130, this corresponds to a liquid color dosage of liquid red HS 130 F-BB of 8%. When considering the water content of the concrete, the amount of water brought in by the liquid paint must be taken into account.

The dosing height at which the concrete is to be colored can be carried out, for example, by choosing from different coloured concrete samples. If required, we are happy to provide these to the architect or planner right from the start of planning. Be careful: these first concrete colour samples are not the same as the test areas required in the “Factblatt Sichtbeton” published by BDZ/DBV.

The concrete recipe is part of the tender to be prepared, in which the concrete paint must also appear. Tender texts should be kept as general as possible with regard to the raw materials to be used, so that there is no influence on the free competition between the various providers. As described above, each manufacturer should also be allowed to choose the form of pigment used. Nevertheless, in order to convey to the concrete manufacturer as precisely as possible which colour is desired, the description of the colour (s) selected by the architect/builder, including its dosage level (s), should be included in the tender text. With our help, concrete plants that use other forms of pigment are able to quickly transfer the described colour to their own system. It is important, and this should also be part of the tender text, that this transfer is carried out in accordance with standards, i.e. that the pigment alternatives must also comply with DIN EN 12878 Category B.

For example, if we assume that the client or architect has opted for red-coloured exposed concrete, coloured with 8% liquid red HS 110 F-BB, then the tender text for the colour to be incorporated into the concrete could read as follows:

Colour: The concrete should be coloured with red iron oxide liquid paint HS 110 F-BB at a dosing level of 8% (corresponding to 4% solid pigment content) or with equivalent products. Alternative pigment preparations or pigment powders of the same shade can also be used for colouring. Coloured concrete test specimens must be provided. As a result of use in reinforced concrete, the pigment or pigment preparation used must comply with DIN EN 12878 Category B. Proof of this must be provided by the paint manufacturer.

Our Scholzianser will be happy to answer any questions you may have about paint and concrete. Just talk to us!