Structural Colors
There are many ways to change the color of concrete, and one of the best is to add the color structurally—before the concrete is poured. When installing a new concrete floor, then there are a couple of options you have for adding the color directly into the structure of the material. Color hardeners and integral pigments can both be mixed into the concrete before it is placed. These allow you to achieve dramatic pattern effects on the surface of the material. Natural pigments, including metal oxides, generally produce more subtle color effects in the concrete. Chemical coloring agents can provide brighter, more eye-catching colors, but they may fade over time. You can also combine structural coloring with parallel and perpendicular etching to create the appearance of grout lines on the floor, in order to simulate a tile installation.
Acid-Staining
Concrete can also be colored after it has been poured and hardened, through a technique known as chemical acid staining–also known as acid-etching. The application of products containing hydrochloric acid and metallic salts to the surface results in a chemical reaction with the lime or calcium hydroxide in the concrete. As the acid etches the concrete surface, metallic salts seep int to cause discoloration. How the coloration unfolds is dependent on a number of factors that are unique to your floor, including its porosity, chemical makeup, age, climate, and composition of the concrete. The results of acid staining are highly unpredictable and will vary across the surface of the floor. However, this is often the desired effect, as the random nature of the chemical process creates a marbled surface that looks very much like natural stone. No two acid-stained floors will look alike, and the beautiful translucent earth tones will be permanent.
Painting
Concrete floors can also be colored the old-fashioned way—by painting them. This is a somewhat controversial treatment in the world of concrete flooring. The problem with paint is that eventually flakes, chips, and fades, and it may need to be reapplied every few years. Painting is especially problematic with concrete floors that lie at or below grade, since these often suffer from moisture issues. If you do decide to paint your concrete surfaces, make sure to use a specially formulated 2-step latex epoxy that is made specifically for this purpose. The benefit of latex epoxy paint is that it creates a waterproof surface over the concrete and acts as a barrier against grease and oil. Painting a concrete floor with epoxy also requires some special preparations steps—you will have to acid-etch the floor prior to application of the paint.
Water-Based Stains
Using a process similar to painting, concrete can also be colored using water-based stains. These stains are substances that penetrate the surface of the floor and cause a chemical reaction with the calcium hydroxide in the concrete, which results in the material taking on pigment. Unlike paint, these stains allow the concrete to breathe, so moisture will not cause the finish to peel or chip away. You can often get much more predictable color effects using water-based stains than you can with acid-staining techniques. And the range of colors is also greater since water-based stains are available in any color you might want.
Tinted Concrete Sealers
A sealer is a chemical agent that you apply to the surface of a concrete floor in order to create a protective barrier that protects it from moisture penetration and stains. In some cases, these sealers can be tinted with coloring agents before application, which imparts subtle shades of hue to the concrete surface when the sealer is applied. However, as the sealers wear off, so will the colors fade. Maintaining the color requires regular reapplication of sealer.
Concrete Dyes
These substances are comprised of very small particles of color, which are able to penetrate down into the concrete floor and directly stain the material. Water-based concrete dyes will produce a more natural marbled look, while solvent-based dyes are better at creating a uniform color effect on the surface of the concrete. One advantage of dyes is that a wider range of bright colors is possible than with acid-staining. Unlike stains, which react chemically with the concrete, dyes are nonreactive, imparting color by simply penetrating the concrete. Dyes are much smaller in particle size than chemical stains, which results in easier penetration and better color saturation, and less residue on the surface. Be aware that solvent-based dyes may be highly flammable, and must be applied under conditions of adequate ventilation.
Textured Concrete
In addition to the various ways that a concrete floor can be colored, it can also be textured and molded in a variety of ways. In the most basic treatment, the floor can be made smoother or rougher during the placement and pouring of the concrete, based mostly on how thoroughly the surface is floated and smoothed during the finishing of the wet concrete. For example, brushing and washing the surface during finishing will create what is known as an exposed aggregate finish, in which the gravels in the concrete will be exposed. This can be a very attractive look. Or, simply brushing the wet surface in one direction after the concrete has been floated will slightly roughen the surface, which can be an advantage in bathrooms where you want to avoid the slipperiness of a very smooth concrete surface.
Polished Concrete
Polishing allows you to achieve the perfect look of glistening stone without having to worry about the maintenance issues. After the concrete floor is poured and set, the material is polished with a series of abrasive pads, progressing from very coarse to smoother and smoother polishing treatments. Generally, concrete is considered polished when it has been treated with 400-grit polishing pads, but some installations will continuing polishing up to very fine 800-grit abrasive pads.
Stamping
Concrete stamping recreates the look of a paved brick or stone surface. It is usually done along with the application of structural coloring. While the concrete is still wet, the installation crew stamps the surface with large polyurethane forms that create a three-dimensional impression in the surface. After the stamping the workers finish the edges and install expansion joints, then seal the concrete. Stamping is more often used for exterior applications, but it is sometimes done for indoor sunrooms, hallways, entryways, or mud-rooms.
Stenciling
Like stamping, stenciling is done after the concrete is poured, floated and edged. Stencils made from disposable paper are impressed into the wet concrete to create the look of bricks, tiles, or pavers with mortar joints. Stenciling is best suited for mimicking the look of ceramic tile or brickwork. This kind of texturizing is sometimes known as etching, though it is an entirely different process than acid-etching, which is a means of coloring concrete.
