Concrete has always been used in construction, where it is appreciated for its strength and durability. From now on, it is acclaimed for the decoration of exterior and interior floors. In this post, we will talk about stained or coloured concrete that is mainly used for decorative purposes. Let’s get started.
Coloured Concrete: All You Need To Know
What is coloured concrete?
Also called tinted concrete or stained concrete, coloured concrete is obtained by mixing sand, cement and gravel, like standard concrete. Depending on the choice of cement, the intensity of the colours of the concrete may vary. For example, using white cement accentuates the luminosity of the concrete, while grey cement gives it a more opaque appearance. The colour of the gravel also has an influence on the final rendering of the concrete.
Where is coloured concrete used?
Very trendy, coloured concrete decorates outdoor spaces such as:
- coloured concrete for terraces
- Garden paths and paths
- Garage descents
- Swimming pool beaches
- BBQ areas
Stained or coloured concrete can be produced in different finishes: simply floated or smoothed, it can also be used as a base for stamped, stamped, bush-hammered, polished, sandblasted, acid-etched or deactivated concrete. With the right concrete staining supplies, you can create wonderful finishes. Each finish has a different surface appearance and texture, and is available in an extensive colour palette.
How to get stained concrete?
The colouring of the concrete is carried out with natural or artificial pigments. These are the ways it’s done:
Surface colouring with coloured hardener
A hardening dye comes in the form of a powder, a mixture of cement, quartz, pigments etc. The quartz-based hardening colourant is applied by dusting on the fresh concrete surface immediately after floating.
After surface impregnation with concrete bleeding water, the surface is then smoothed. As it dries, it forms a protective film (wear layer) and colours the concrete to a low thickness (a few mm, depending on the quantity applied).
Once stained, this type of concrete can receive a smoothed finish manually or mechanically. It can also be stamped, printed or polished.
Concrete stained with coloured pigments
Stained concrete is obtained by incorporating a powder or liquid dye directly into the cement mixer, the mixer of the concrete plant or the mixer at the time of manufacture.
The concrete coloured in the mass can receive a floated or smoothed finish (manually or mechanically), stamped, bush-hammered, polished, sandblasted, acid-etched or deactivated.
Depending on the finish chosen, the use of coloured sand and/or gravel in addition to colouring the binder also plays a role and gives special decorative effects.
What colours can concrete be stained with?
When it comes to concrete colour, anything is possible. The limit is based on the colours offered by the ready-mixed concrete supplier or your imagination if you make your mix with a cement mixer.
Black concrete and white concrete exist. As in interior decoration, these two colours are very popular for their elegance. Black adds a refined touch and gives character to exteriors. White illuminates and enhances your home.
Between the two, an infinite number of colours are possible thanks to natural (iron oxide) or synthetic dyes.
What are concrete colourants used for?
Pigments are used to colour concrete, mortars, or coatings in the mass.
By using pigments you can make decorative concrete slabs (exterior coloured concrete driveway or terrace, stamped concrete, deactivated concrete, etc.), coloured poured concrete walls, coloured screeds, coloured levelling compounds, coatings coloured or coloured cement.
What are the types of concrete colourants?
Concrete dyes are used to colour concrete, mortars, coatings or even cement in the mass. The colourants used in concrete are coloured pigments (a special type of colourant).
They consist of very fine colouring particles (0.1 to 1 micron). They are added in small quantities to the concrete when mixing. Dispersed evenly in the concrete, they make it possible to obtain a homogeneous and lasting colouration.
Different types of colourants are used to colour the fresh concrete in the mass.
Concrete pigments can be of synthetic origin (iron oxides, metal oxides, carbon black) or of natural origin (earthy tones, ochres, ores). The most commonly used dyes are based on iron oxide.
These different types of pigments are:
- In powder form, most of the time.
- In granular form as well (pigments in powder agglomerated in the form of microbeads of 30 to 500 microns). Granulated pigments are easier to handle, disperse more easily and have better tinting power.
- In aqueous suspension (liquid or paste). The pigments in aqueous suspension facilitate the dosage which can be volumetric and also facilitates the dispersion of the pigment during mixing.
The pigments used in construction materials based on cement or lime must comply with regulations and standards.
How are concrete colourants dosed?
The dosage of a concrete colourant is generally expressed as a percentage of the colourant relative to the weight of cement used in the concrete formula.
Thus, if we define a dosage of 5% of colourant relative to the mass of cement, for concrete having a cement dosage of 300 kg/m3, this is equivalent to introducing 15 kg of colourant per cubic metre of concrete.
For large volumes of concrete (in the case of coloured concrete for terraces), it is advisable to use ready-mixed concrete that has already been coloured. The dyes are dosed and introduced to the concrete plant.
Plants generally use pre-dosed 5kg bags of colourants, which are introduced into the concrete mixer at each batch. Dosing the dye is then simple: the operator just has to count the number of bags to be introduced according to the volume of concrete produced.
For smaller volumes of concrete made with a cement mixer, the dosage of the dye is done by weighing the quantity of dye to be introduced for each batch.
Commercially available powder dyes are usually packaged in 1.5 litre tubs. The dosage is listed in the instructions for use of the pigment. Generally, the consumption is 1 dose (jar) for 1 bag of cement.
If you need to achieve a very precise concrete colour, you should know that the colour of coloured concrete results from that of the cement, the sand, the dye and its dosage.
The dosage of the dye must therefore be adapted according to the desired shade and colours and the different constituents (cement, aggregate, etc.).
Light or pastel coloured concrete is made with white or light grey cement and pigment dosages of between 0.5 and 1.5% of the mass of cement.
Brightly coloured concretes are obtained with high pigment dosages (up to 5%).
For shades far removed from natural concrete (yellow, green, blue) white or light grey cement is used.
For dark colours (red, brown, and black coloured concrete), conventional grey cement is used.
Concrete colourants: Usual dosage
The most frequent doses are, for common colours (red, brown, ochre, black), between 3 and 5% of the mass of cement (i.e. for a concrete dosed with 300 kg of cement between 9 and 15 kg per cubic metre of concrete).
It is generally advisable to avoid the use of dyes whose colour is opposite to that of the aggregates (sand in particular). For example black, brown or red dyes with white calcareous sands. Or even yellow pigments with black sand.
What are the benefits of stained concrete?
- An exterior stained concrete ensures both the creation of an operational surface for a given use and a personalised decoration. It is a good alternative to concrete slab type solutions with glued tiles. It avoids the classic problems of detachment or poor frost resistance.
- Thanks to the wide range of possible colours and the numerous surface aspects available depending on the treatments, coloured concrete offers great creative freedom in the design of facilities. It can aesthetically integrate with all types of sites and respect their architectural environment. With a little imagination, it is possible to obtain a highly personalised decoration.
- In addition, the maintenance of this floor covering is very low and its colouring is durable (much more durable than a coat of paint or coloured resin), especially when it is coloured in the mass.
What are some drawbacks of stained concrete?
- For a given colourant, the use of white cement or grey cement in the concrete mix does not give the same tint. Some pigment suppliers present as an indication of the expected colours depending on the cement and the dye dosage, but there are inevitably variations.
- The colour also varies according to the drying conditions of the concrete. Thus, two concretes made on different days will not be the same colour.
- Finally, you should know that the poured concrete, once dry, is lighter than the mixture in the fresh state.
Also, it is better to make samples beforehand to know what to expect. The application of a stain protection product after about 20 days of drying time will allow you to revive the colour of the concrete and facilitate its maintenance.