The last thing you as a contractor or specifier want to hear when you complete a decorative, colored concrete installation (integral, dry-shake, stamped, textured, stenciled, or trowel finished) is that the owners are unhappy because the color wasn't what they ordered. Then you find yourself in the awkward position of telling them that the color is right, but efflorescence has lightened its appearance. Owners frequently respond to that news by stating they want the color they ordered before they will pay for the job. What to do?
Efflorescence is soluble salts that dissolved in water moving through concrete and then precipitated onto the slab surface. These salts can originate in the subgrade, in the aggregates in the concrete, or in the cement paste. Many of these salts are water-soluble and can be removed easily after they are deposited on the surface. But the salts that form carbonates (combine with atmospheric carbon dioxide) are more difficult to remove, and are the subject of this article.