A Guide to Stamped Concrete Colors

Changing the color of a stamped walkway

Question: How can I change the color of a stamped slab after it has been poured? The customer was not happy with gray and now wants a reddish-brown color.

Answer: You can change the color of stamped work once it has been placed by applying different types of stains, tints, or dyes. The type of coloring method you use will depend on the look desired and amount of color changed needed. Here's a handy guide:

For most decorative stamping work, lighter base colors

• For minor color adjustment - Use an impregnating stain or diluted acid stain.
• For medium color adjustment - Use a full-strength acid stain, dye, or tinted sealer.]
• For complete color change - Use an acrylic or solid-color stain.

When using any of these methods to change or adjust concrete color, be sure to profile the surface according to the product manufacturer's recommendations to ensure proper penetration and adhesion. In addition, the surface should be completely dry and the temperature above 50 F and below 90 F.

Finally, no matter what method you use, always prepare a small sample for pre-approval by the client.

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Excess antiquing color causes problems

Question: I have a pool deck in which the sealer seems to be flaking off and coming up in some areas. This is not an issue that we have dealt with before, so I am a little concerned. Can you let us know what is occurring and how we can remedy this issue?

A good rule to work by is that secondary color should make up 5% to 30% of the final color. In this case, the secondary color makes up almost 100% of the surface color, causing sealer failure.

Answer: This is actually one of the most common issues we face with coloring stamped concrete. It is in fact not a sealer issue, but rather the antiquing color that is causing the sealer to fail. The sealer failure can occur within weeks of application, but more often shows up 6 to 12 months down the road.

Imprinted concrete looks pretty bland and unrealistic without highlights or antiquing, which give the pattern definition and color variation. These highlights make the concrete look like stone, tile or whatever natural material the installer is trying to mimic. The highlights can be accomplished in a multitude of ways, with release powder being the most common. Other popular methods include stains, tints, dyes and colored sealers. Virtually any means of getting some contrasting color to stick in the depressions and textured areas of the surface will work. The problem occurs when too much secondary color is present. The depth and type of texture on the imprinting tool will determine the amount of secondary color to use. More aggressive textures with deep grout lines, lots of deep veins, and rough slate or stone surfaces will accommodate more secondary or antiquing color. The opposite holds true for light textures with smoother surfaces and non-aggressive patterns. A good rule to work by is that secondary color should make up 5% to 30% of the final color. In your case, however, the secondary color makes up almost 100% of the surface color.

The real curve ball is that stamped work with such high ratios of secondary color can look amazing and beautiful. Once sealed, the work looks great, the applicator gets paid and everyone is happy. The problem is that you have ticking time bomb, and it is just a matter of time before it explodes. Have you ever considered what secondary color is made of and how it works? No matter whether you use release powder, stains, washes or tints, you are filling the surface pores of the concrete with solid material. Those solids are filling the voids that the sealer needs to fill in order to "bite" or adhere to the concrete. The more secondary color present, the bigger the problem. The sealer will encapsulate the solid color in an attempt to do its job, but if there are no pores to fill, adhesion is compromised, which leads to failure when external forces exceed the ability for the sealer to hold. This is usually why we see these types of failures in the spring, after a winter assault of freeze-thaw cycles, deicing salts and snow shovels. As a result, the sealer lifts up in small circular areas and takes the secondary color with it, since the color is all it had to hold onto. You are then left with a stamped slab that has round, discolored spots. The "discoloration" is actually the base color that should have been visible in the first place, but was covered with too much secondary color.

The repair is fairly simple in theory, but more difficult in practice. The sealer has to be chemically stripped, but the process will usually remove most of the secondary color as well. Once the stripping is complete, you can remove any residual secondary color, give the surface a good cleaning, and then allow it to dry before resealing. The hard part is selling the client on the new "correct" color combination of their patio. What was mostly dark brown with hints of tan is now mostly tan with hints of dark brown.

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Concrete coloring techniques

Question: What is the difference between base color and secondary color in stamped or imprinted concrete?

Answer: The base color refers to the primary color of the concrete. Most stamped concrete is colored with pigments that are either added to the mix (integral color) or surface applied (shake-on color hardener). While both are good methods of coloring concrete, color hardener provides greater color selection and enhances the strength and durability of the concrete surface.

For most decorative stamping work, lighter base colors
are accented by darker secondary colors. In this case,
he results mimic naturally weathered stone.

Secondary colors are used over the base color as contrasting accents or highlights. The contrast is what makes stamped concrete come alive, and provides the perception of stone, tile, wood, or rock. There are many different products and methods for imparting secondary color, depending on the final look desired and the applicator's preference. These include, but are not limited to, pigmented release powder, tinted liquid release, stains, tints, dyes, and tinted sealers. The most common, and arguably most practical method for adding secondary color to stamped concrete, is to use a pigmented release powder during the stamping process.

There is no limit to the number of base or secondary colors that can be used. In fact, blending multiple colors, in both the base and secondary applications, can add to the overall realism of the results. An important factor to keep in mind: The secondary color should make up no more than 40% of the final color you see. Anything more then that can impair the adhesion of the sealer to the concrete surface.

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How to remove too much colored release agent

Question: I installed a stamped concrete slab for some homeowners, and they decided they wanted more of the colored release agent removed from the slab after I had already sealed it. They thought it looked too dark. How do I remove the sealer and wash off the release to reduce the intensity of the secondary color?

Answer: When concrete is stamped using colored antiquing release, the stamps actually push some of the colored powder into surface of the concrete. This process causes the secondary color to be permanently encapsulated in the surface paste of the concrete. So, without writing a Master's thesis and getting into a lot of chemistry, I will keep it simple and tell you that it will be very hard to remove the colored release powder if the slab was stamped properly. The sealer, however, can be removed with a chemical stripper (see Advice on Using Chemical Strippers and The Concrete Network article Best Method for Stripping Sealers).

During that process, you may be able to remove some of the release color. Try attacking the concrete with a stiff-bristle brush, and scrub until you remove some color. This can take a long time, and produce a lot of sweat. If you need to remove more color, try using a very dilute acid (40 parts water to 1 part muriatic acid). Spray down the dilute acid, covering small sections of the slab at a time, then scrub it in with a brush and rinse with soapy water. The acid will actually take up some of the concrete paste, along with some of the color. Test this in an inconspicuous area first to be sure you are getting the results you and the homeowners desire.

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