In patching small surface defects in concrete, is there a precise way to assure that the color will match?
This isn't the easiest thing in the world to do, but it can be accomplished with a little care and persistence. The important factor to take into account is that the patch will almost always dry to a darker shade than the original concrete. This can be prevented by using a mixture of white and regular portland cement. If the match must be exact, it will be necessary to make experimental patches using various proportions of white cement and regular cement. Comparison of the concrete to be matched and the samples should be made when the materials have dried thoroughly to determine which blend of the two cements comes closest to matching. If possible the same sand should be used for the patching as in the original concrete, and it is even desirable to maintain the same proportion of sand and cement. The mix should be of very stiff consistency--just workable enough to place.