Concrete is gray, massive and simply ugly. But it does not have to be like this. While modern technology is making concrete shapes ever more organic and slimmer, you can do it yourself Go a different way with your private projects: How about an alternative to the dreary Gray? We explain the methods and work steps you use to color concrete in a targeted manner.
Why gray
Why should you even think about coloring your concrete yourself? Can't the manufacturers do that directly? It doesn't always have to be gray. Well, it doesn't always have to be gray, but unless you make additional efforts, concrete is and will inevitably be reserved for this color shade. The reason is the most important ingredient in concrete: cement. In addition to a few other additives, it is primarily made from limestone and clay, naturally occurring in the form of a mixture, usually as so-called "marl". The raw materials are burned at almost 1,500 degrees Celsius above the so-called sintering limit and then ground into the familiar powder. Both the raw materials themselves and the firing process lead to the well-known, unappealing color.
How do you change the concrete color?
Various manufacturers have also recognized that additional colors increase diversity and make concrete interesting for people who want to avoid the uniform gray. For large quantities of concrete, for example when building a house, the coloring should be left to the professionals. But if you need smaller amounts of concrete for garden walls, planters or handicrafts, you can create the desired color yourself using the means described below. Regardless of the method chosen, various substances are added to the concrete and thus a coloration
The preliminary considerations
Before coloring, you should be aware of a few things:
1. The starting color
Since cement is naturally gray, it is very difficult to achieve bright, bright colors. If you are aiming for light colors, you should therefore use so-called white cement for your concrete. This is by nature not pure white, but significantly lighter than the familiar gray. The reason for this is the very low proportion of darkening iron oxides.
2. Aggregates
Often sand or gravel are used as aggregates in concrete. Of course, these cannot be colored through and are recognizable as non-colored particles in the later concrete. While sand only appears as a lightener of the color shade, with gravel every single pebble is the has made it to the concrete surface, at the latest in the course of time through the flaking of the thin cement veil readable. This effect can be used in a targeted manner, but can inadvertently impair the result if it is not taken into account.
3. The amount of pigments
Regardless of the pigment described later, the concrete's absorption capacity for the dyes is limited. As a rule, if the amount is increased by more than five percent of the cement content, no further change or intensification of the color can be determined. The concrete is thus saturated. If lighter colors are to be achieved, however, the proportion can be reduced so that pigment proportions between two and the final upper limit of five percent are often used
4. Efflorescence
Over time, every concrete secretes a certain amount of salts and other chemical compounds on its surface. One speaks here of the so-called blooming. This mostly light to white layer means that the natural gray, as well as added colors, appear lighter. The efflorescence can be removed by water pressure or sanding, but can reappear. As a result, for example, an initially deep black concrete will in most cases give way to anthracite or even very dark black-gray in the long run.
The processing
The pigments added to the concrete are always processed in the same way, regardless of the type of pigment:
- Required volume of concrete determine
- Determine the amount of cement for the volume of concrete according to the manufacturer's instructions, taking aggregates (sand, gravel) into account
- Weigh the pigment according to the manufacturer's instructions in relation to the amount of cement
- If available, use the manufacturer's color scale to determine the proportion of pigment to cement
- Thoroughly mix the pigment and dry cement to avoid color pockets later
- Create and process concrete in the usual form from pigment-cement mixture, water and aggregates
ATTENTION: It is advisable to wear protective goggles and a dust mask not only for the very fine pigment, but also for handling the harmful cement. The finest particles can get into the airways or eyes and cause permanent damage.
Common pigments
There are different pigments that can be used to color concrete. Here you will find the most common and practical ones.
Professional pigments
Various manufacturers now offer specific pigments for coloring concrete. The color palette is constantly increasing and already includes all common main colors. The gradation of the hue, on the other hand, is controlled by the amount of pigment added.
basalt
The pigment of the same name, ground from basalt rock, is available from artist supplies. Although the stone powder is usually gray to olive-green in its pure form, it turns the concrete into a strong black color. Depending on the dosage, colors from anthracite to various shades of gray can also be achieved.
Copper oxide
The copper oxide, also known from horticulture as a weed killer, can also be used as a pigment. Depending on its chemical composition, it usually achieves green, less often green-brown colors.
Iron oxide
Like iron
If human blood stains red, it is in the form of iron oxide capable of staining concrete in shades of ocher to brownish-red. It is available from artist supplies, as well as from numerous handicraft or chemical supply stores.ATTENTION
Again and again one reads about coloring concrete with the addition of soot or charcoal powder from dark to black. Although darkening is achieved in this way, these substances are organic compounds, so that neither the durability nor the effect to be achieved are guaranteed. The durability of the concrete itself can also be affected by the addition of organic substances to its basic mineral substances. We therefore strongly advise against using charcoal or soot for coloring concrete!
Special case of oil shale cement
If you are aiming for a red-brown color, you can use a special cement, the so-called oil shale cement, instead of additional pigments. Instead of the normal marl, it is made from oil shale, ultimately a special form of clay and limestone. It creates a reddish brown hue on its own, but it is more expensive than regular cement in terms of cost. Here it is important to weigh up the cheaper option before buying - oil shale cement or normal cement with pigments.
Coloring with aggregates - the alternative
Instead of coloring the cement and thus the core element of the concrete, there is another way of influencing the color. Today there are a large number of different types of gravel and gravel, which differ greatly in their color. The technical suitability of these types of gravel is hardly relevant for less stressed concrete, such as in horticulture. Instead, by choosing a strong, intense color, a clear contrast to the gray of the concrete can be achieved. How about, for example, deep black or pure white gravel in the gray of the cement? While the colors are easy to distinguish from close up, the human eye mixes them together from a distance and achieves a uniform mixed tone of both colors.
Pigmented glazes
Finally, the possibility of coloring existing concrete components with glazes with a pigment content should be briefly addressed here. The manufacturers of these products claim that the pigments penetrate a little deeper into the material due to the suction effect of the concrete pores and thus actually color the concrete. However, since the depth of penetration is very limited, it is - as long-term observations show - ultimately more of one very durable surface coating, which in the strict sense does not belong to the possibilities of concrete coloring.