Question: Construction contingencies caused us to end up with a one-panel gap in a driveway. Later we filled this in with another load. We have learned that the Portland cement in the last load came from a different cement plant from the rest. Could a change in cement cause this much change in color? Is there anything we can do to correct it?
Answers: A change in brand or type of cement almost always causes a change in color, not always as dramatic as in your experience. Making the exceptional panel match the others would be difficult. You might try a stain, in consultation with the manufacturer, but success would probably require some artistry to get a good match, and it is not certain that the color would continue to match after weathering.If it is important enough to have a precise colormatch it could be accomplished by taking out the whole panel and replacing it with concrete made with the same cement and mix proportions as the adjacent sections, and curing it in the same way. Any changes in materials might lead to another difference in color, though not likely as marked as before.A less satisfactory solution would be to make a grout mix using 1 part of the correct cement and about 3 parts by volume of minus 30-mesh sand and water. This could be scrubbed into the predampened surface and a curing compound applied. (If there is still any curing compound on the original surface, a couple of months should be allowed to elapse before coating so that the curing compound will disappear. Any dirt that accumulates in the meantime should be scrubbed off and the surface thoroughly rinsed.) A trial mix would have to be made, applied to a limited area, cured 3 days and allowed to dry. If too dark, the mix could be adjusted by replacing some grey cement with white cement. If too light, the cement content could be increased slightly. The problem with this treatment is that the coating might wear off before long.Another possibility is to accentuate the difference with plantings or decorative side strips to make the effect look intentional.