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Chris Sullivan
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Not all efflorescence is undesirable. Here it's being created intentionally to lighten integrally colored concrete that's too dark.

Question:

I have an integrally colored driveway that was supposed to be light gray, but the ready mix supplier used the wrong color and now I have a black charcoal driveway. Is there anything I can do to change the color from black to light gray? Part of the driveway is broom finished, while some of it is exposed aggregate.

Answer:

This is one of the hardest issues to deal with. Because integral color is such a durable and "integral" part of the concrete, it's very difficult to change the color. Going from a light to a dark color can be achieved with tinted sealers and colored coatings. But to go from dark to light, without making the surface look like it has been painted, often requires application of a micro-thin colored overlay. However, this is a costly fix and will not work over exposed aggregate.

One off-the-wall method I have recommended that has proven successful in certain cases is to purposely try to generate the formation of efflorescence. Yes, that naturally-occurring white salt residue that most people want to eliminate from their colored concrete because it has a natural lightening effect (often mistaken for color fading). In this case, though, you want to reduce the color intensity and tone down the darkness from black to gray, and efflorescence can help you do that. For this to work, the concrete must be free of all sealers and curing compounds. Use a garden hose or pressure washer, and saturate the concrete surface with lots of water. Then let Mother Nature take effect. Multiple water-soaking cycles may be needed, and there is no guarantee that the color will lighten to the desired shade, if at all.

Another strategy that can help in this situation is not to use a topical membrane-forming sealer. These products will enhance the color and darken the substrate. Consider using an internal impregnating sealer that will penetrate and seal the concrete, but not darken the color.

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Author Chris Sullivan, ConcreteNetwork.com technical expert and vice president of sales and marketing for ChemSystems Inc.


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