There can be many reasons why decorative concrete installations don't go well, and some of those reasons have to do with incompatibilities with concrete admixtures. As a contractor you will need help from your manufacturer's representative in order to understand some of the problems that can result. If you are trying to do something you haven't done before, you'll need to know more about what could happen. Here are a few incompatibility issues of which you should be aware.

Integral color

Adding color to concrete can result in increased air entrained into your concrete mix. Discussing this with the color manufacturer you are using and with your ready-mix producer will provide the answers you need. If there are lingering doubts, check the air content of the first loads of concrete delivered to your job.

Some manufacturers of powdered integral color include water-reducing admixtures in the color to help disperse the color more evenly throughout the concrete. As a result, less water is needed in the mix to achieve the

Chemical stains work well when admixtures don't reduce the amount of calcium hydroxide in the surface of the concrete.
Miracote, a division of Crossfield Products Chemical stains work well when admixtures don't reduce the amount of calcium hydroxide in the surface of the concrete.

same placing slump, which should be considered in the mix design. These water reducers also retard the set of concrete, which could be a problem if additional retarding agents are added to the mix without knowing the impact of those in the color. Admixtures included with the color also can pose a problem when concrete is placed at lower temperatures.

Some manufacturers of powdered integral color use naphthalene-based admixtures to enhance the dispersal of color in the concrete. If you were to also use a polycarboxylate super-plasticizer to improve placeability of the concrete, the two admixtures could cancel out each other's effect. The amounts of each material in the mix will influence this reaction, but if this occurs you will notice that the placement slump of the concrete is less than expected.

Manufacturers also use chemicals to hold colors in dispersion for liquid-dispensed integral color systems. These chemicals do not, however, react with other admixtures to cause problems.

Adding calcium chloride to colored concrete (integral or color hardeners) is unwise because it causes the colors to look mottled. Although today there are some designers who like this look, to be safe, provide a sample for approval

Chemical stain incompatibilities

When chemical stains are applied to concrete surfaces, they develop color by reacting with calcium hydroxide, a byproduct of the hydration reaction of portland cement. When there is an abundant supply of calcium hydroxide, the reaction results in more intense colorations. Some admixtures, however, limit the amount of calcium hydroxide available for the stains. Pozzolans, such as fly ash and metakaolin, also can react with calcium hydroxide to produce additional cementing materials and, as a result, there is less available for stains to react with.

If you want strong concrete with a low water-cement (w/c) ratio and use superplasticizers to place the concrete, the result will be concrete with less calcium hydroxide and a denser surface that is more difficult for the stain to penetrate. The superplasticizers don't contribute to this reaction; they just make it possible to place the low w/c material.

What to do?

When you decide to try something new, don't experiment on the jobsite. Try it on samples first. When admixtures are involved discuss your approach with your color manufacturer's representative (you should get to know them anyway). Also discuss your plans with your ready-mix producer because they too have a wide range of experience. The object is to proceed from an informed viewpoint.