Methods of Coloring Stamped Concrete
You can get the look and feel of stone, brick, slate, and other rough-textured materials with stamping mats and skins. But to complete the effect, you also need to replicate the natural colors of those materials. There are four options contractors typically use to color stamped concrete. Most often, a base color is first used through an integral color or dry-shake hardener. Then to achieve a more natural, variegated appearance, an accent or antiquing colors using pigmented powdered or liquid release agents are used, possibly supplemented by stains, dyes, or tints.
Advantages: Easy to use. It is mixed into the concrete at the batch plant providing uniform, homogeneous color. Color is permanent because it extends throughout the entire matrix of the concrete. If the slab is accidentally chipped or scratched, the integral color will remain.
Disadvantages: The color options are typically more subtle and less vibrant that what you can achieve with color hardeners. Integral are therefore most often used in conjunction with surface-applied treatments, such as color hardeners, and chemical stains.
Dry-Shake Color Hardeners
Advantages: Produces brighter colors, and comes in unlimited range of color options. Hardeners are broadcast onto the fresh concrete and then floated into the surface. Because the product contains fine aggregate and cement, they help densify the surface, making it less permeable.
Disadvantages: More labor-intensive because they must be hand-broadcast. Hardners are only applied in the quantity needed to color the top 1/8 to 3/16 inch of the slab (resulting in savings on cost), but the underlying plain gray concrete can show through if the surface is marred deeper than those levels.
Powdered or Liquid Release Agents
Advantages: Both of these products help prevent the stamping mats or skins from sticking to the concrete and spoiling the texture. They also impart subtle color that enhances integral or dry-shake color, resulting in an antiquing effect. A popular technique is to start with a light base color with an integral color or hardener, and then apply a much darker release agent for contrast.
Disadvantages: The powdered release agents are very fine powders that are airborne and can stain nearby buildings, or existing flatwork. Powders require more clean up and masking of adjacent surfaces, but they produce greater contrast than a liquid release.
Advantages: Stains react chemically with the concrete and produce a mottling effect that gives stamped work a sense of realism. You can apply stains randomly to individual stones in the stamped design (which is something that can't be achieved with integral color or hardeners).
Disadvantages: Stains produce natural coloring and are transparent. They can be used in conjunction with dyes to achieve greater color intensity.
For more information about coloring processes for stamped concrete, refer to the book Bob Harris' Guide to Stamped Concrete.