The public has come to thick of concrete as a decorative as well as utilitarian material. As a result, their standards for its surface appearance have rose considerably. They except concrete in its many guises- floors, sidewalks, driveways, patios, and walls- to be attractive. But concrete can become discolored due to conditions present in the concrete itself or as a result of external factors. Discoloration arising from problems due to the concrete mix design and ingredients, and concreting practices before the concrete has hardened ordinarily take on one of three forms: (1) large areas of contrasting color, (2) black spots or dark "leopard" spots; and (3) white patches caused by efflorescence. Factors which can result in surface discoloration include color and composition of the cement, water/cement ratio, curing, admixtures, and finishing practices. For large areas of contrasting color caused by different concrete making materials, the only corrective treatment for this type of discoloration is the application of some type of opaque coating. This coating could be paint; or in the case of colored concrete, the use of one of the floor waxes in various colors offered by some manufacturers to match their color floor shake materials. Dark spots can be removed with a single washdown of water if concrete does not contain calcium chloride. In concrete containing calcium chloride, it is often necessary to wash the area several times. It appears that best results are obtained when such discolored concrete is washed soon after the spots appear. Light spots are usually more difficult to remove. Repeated washings or weathering often causes the dark background to lighten, approaching the shade of the spots. A chemical corrective treatment often used to eradicate light spots is the application of a strong lye wash. The most effective treatment for efflorescence is generous, prolonged flushing of the surface soon after the efflorescence appears. Scrubbing the set concrete with a very stiff non-metal brush also will sometimes be of help. Discoloration can also be caused by materials that are spilled or come into direct contact with concrete. Iron stains can be recognized by their rust coloring and their proximity to iron or steel objects. To correct: mop the surface with a solution of one pound of oxalic acid powder per gallon of water; after 2-3 hours, rinse the surface with water and scrub it with stiff brushes or brooms. For aluminum stains, scrub the surface with a muriatic acid solution. Ink stains may be removed by the application of a sodium perforate poultice.