Tag Archives: inconsistency

Achieving color consistency in concrete countertops: Part 3 of 3

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You have learned that water strongly affects the color of a concrete countertop mix, as does precision of measuring and measuring by weight, not volume. This final article in the color consistency series lists several other reasons you might encounter inconsistency in your concrete countertop mixes.

  • Variability in the ingredients themselves

From year to year, the ingredients you use can vary, even if you buy the same ingredient from the same manufacturer. Pigments tend to be very consistent, but cements, especially gray cements, are not. Your colors that have less pigment, and therefore obtain most of their color from the cement, will exhibit more variability thann heavily pigmented colors.

  • Use of pozzolans

You may use pozzolans such as metakaolin, VCAS, fly ash, slag or silica fume in your mixes. Some of these pozzolans, especially waste products such as slag, can be highly variable in color. And, pozzolans such as silica fume can impart a very distinct color to the concrete. Besides the fact that different pozzolans have different actions and properties, you should not vary which pozzolans you use in your mix designs if you want to achieve color consistency.

pozzolans

Various pozzolans. Photo courtesy www.cement.org

  • Use of admixtures such as superplasticizer

Admixtures like superplasticizers can influence color, not because they add color, but because they can act like dispersants, aiding in cement and pigment dispersion and the resulting color strength. Other admixtures usually have little effect on the color, like fibers, accelerators or retarders, however calcium chloride accelerators are an exception and should be avoided for this and other reasons.

  • Not blending ingredients thoroughly

Thorough and complete blending of all of the concrete ingredients is very important to achieving a uniform and consistent color. All of the pigment added to the mixer should be uniformly blended. If pigment is stuck to the sides of the mixer or in lumps or streaks then the resulting concrete will not be consistent with other batches nor will the color of that batch be uniform.

  • Adding liquid pigment to the mix water

Adding liquid pigment to the mix water before adding the now pigmented mix water to the concrete can cause color inconsistency because a significant amount of the pigment usually remains in the bucket.

Liquid pigments are really ultra fine pigment particles suspended in a liquid. If the liquid pigment is added to mix water, the pigment particles will quickly settle out because the suspension fluid is now greatly diluted by the mix water. No amount of stirring will suspend all of the pigment particles, so much of the color remains in the bucket rather than going into the mixer.

When done carefully, it is possible to add the liquid pigment to a portion of the mix water and then use the remaining mix water to rinse out any pigment residue.  But this involves extra work and requires extra attention. A simpler process would be to add the liquid pigment directly to the mixer and then to rinse out the pigment container with the mix water as it is added.

  • Inconsistent curing practices

Curing the concrete has an effect on concrete color. Curing the concrete after casting helps “lock in” the color. If some slabs are allowed to wet cure for longer than others, the slabs that dry out sooner will appear lighter.

  • Forms

Forms for fluid concrete mixes must be watertight in order to achieve consistent colors. Otherwise, color variations will show where some of the concrete leaked out of the forms. Form materials themselves (the texture and porosity) can affect the color of the concrete too.

Conclusion

Everything that goes into making concrete has some effect on its appearance. Discipline, attention to detail and knowledge of good concrete practices will make your concrete countertops as consistent as possible.

Achieving color consistency in concrete countertops: Part 2 of 3

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The last article talked about the importance of measuring ingredient precisely, especially water. It is also very important to understand that you must measure by weight, not by volume.

Suppose a mythical concrete countertop mix included cotton balls as one ingredient and golf balls as another. Clearly a much larger volume of cotton balls would be needed to make one pound, versus one pound of golf balls.

There are some ingredients which seem to have consistent weight-volume conversions, such as water. You know that one quart of water is 32 (fluid) ounces. So you could just measure your water using a container with ounce or quart markings on it, right?

Not so. Measuring containers are typically not designed to a high degree of precision. Watch this video to see why using measuring containers can lead to errors and inconsistency.

Achieving color consistency in concrete countertops: Part 1 of 3

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Integrally colored concrete countertops can show color inconsistency for a variety of reasons, but the primary cause is lack of ingredient control: One or more of the ingredients in each batch of concrete were not carefully proportioned.

Most often the culprit is water. Adding too much water – often to increase the workability – will alter the color of the concrete, making it lighter than a similar batch that has less water in it.

Think of grape Kool-Aid. The more water you add, the lighter the color will be. The same applies to concrete. (The concrete will also be weaker, just like the Kool-Aid will taste weaker.)

Kool-Aid

Remember, water is the most critical ingredient in concrete, and casually adding water without keeping track of the exact amount will almost guarantee an inconsistent appearance. To ensure color consistency, ALL of the ingredients, including water, must be accounted for.

The simplest way of doing this is to generate a batch report, where each ingredient amount is listed next to a check box. The batch report ensures consistency in ingredient amounts, and the check boxes ensure that none of the ingredients gets left out.

The CCI mix calculators, both the Precast Concrete Countertop Mix Calculator and the GFRC Concrete Countertop Mix Calculator, print out batch reports. Whatever method you use to calculate your mix, make sure that you are diligent about using batch reports.