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Recipe: Coloring Concrete

For coloring concrete, highly alkaline-stable pigments are necessary. Particularly suitable for this application are iron oxide pigments. For light colors, it is preferable to use white cement. A pigment can only color the cement matrix, not the aggregate. It is possible to add selected white quartz sand, cristobalite or colored stone powders. To achieve a certain color hue, it is always necessary to make tests prior to application, because the color will change when the concrete hardens and dries. The cement matrix will react differently, depending on the pigment: · The pigment particle reacts with the cement and stabilizes the matrix: all red, brown and black iron oxide pigments. · The pigment behaves like a sand particle: most metal oxides, inorganic pigments, such as cobalt pigments, nickel-titanium-yellow, titanium dioxide. · The pigment particle will weaken the structure: clay minerals, slate powder, green earth pigments and similarly swellable minerals. · The pigment particle can be mixed into the cement, but will always remain a foreign body within the cement matrix: synthetic-organic pigments. These pigments can be washed out of the concrete or plaster by water, therefore they are not recommended for applications in exterior or wet areas!

Processing

The pigment powder has to be mixed thoroughly with the dry cement powder. If the pigment is not thoroughly dispersed, pigment agglomerates can not only weaken the cement structure but, they may also cause “bleeding” of the color later on. Step 1#242: The pigment powder has to be mixed thoroughly with the dry cement powder. If the pigment is not thoroughly dispersed, pigment agglomerates can not only weaken the cement structure but, they may also cause “bleeding” of the color later on.
If only small amounts of cement are to be colored or if you do not have a proper machine at your disposal for mixing the cement, it may be easier to use color pastes or to disperse the pigments in water first. In this case, it will help to soak the pigments in water overnight (add the pigment to a bowl with water and let them sink in, do not stir until the next day!). Stir the pigments into the mixing-water before adding it to the cement. Step 2#442: If only small amounts of cement are to be colored or if you do not have a proper machine at your disposal for mixing the cement, it may be easier to use color pastes or to disperse the pigments in water first. In this case, it will help to soak the pigments in water overnight (add the pigment to a bowl with water and let them sink in, do not stir until the next day!). Stir the pigments into the mixing-water before adding it to the cement.
The amount of pigment depends on the desired color, though more than 4 % pigment should not be added to pure cement (based on the amount of cement). If a concrete or mortar is supposed to be colored, the share of 4 % may already be too much, because the mortar will also contain aggregates and will not be able to bind as much pigment. Also, if very fine synthetic-organic pigments are used, 4% may be too much. Step 3#411: The amount of pigment depends on the desired color, though more than 4 % pigment should not be added to pure cement (based on the amount of cement). If a concrete or mortar is supposed to be colored, the share of 4 % may already be too much, because the mortar will also contain aggregates and will not be able to bind as much pigment. Also, if very fine synthetic-organic pigments are used, 4% may be too much.
Mixtures might also act differently if the concrete contains additional aggregates, because the cement then not only needs to bind the sand, but also the fine pigment particles. If the amount of pigment added is too high, the stability of the concrete may be reduced. Or: If a very fine pigment is added, the amount of cement has to be increased. Step 4#346: Mixtures might also act differently if the concrete contains additional aggregates, because the cement then not only needs to bind the sand, but also the fine pigment particles. If the amount of pigment added is too high, the stability of the concrete may be reduced. Or: If a very fine pigment is added, the amount of cement has to be increased.

Ingredients

cement-resistant pigments
cement powder
Water
colorless sand

Additional Information

Pigment suitability lists

Note

Add 10% of Plextol D498 in order to preserve the pigment from being washed out and to enhance the strength of corners and edges. This only applies only frost-free areas, though. Since cement is very alkaline, only alkaline-stable pigments can be used to color concrete or cement-based mortars.

We assume no liability for the processing instructions described above. In any case, we recommend the production and evaluation of sample surfaces.