Although curing of concrete flatwork is not an integral part of placing and finishing operations, it is still indispensable in producing an acceptable finished product. Unfortunately, curing is often completely neglected or improperly or inadequately done. Properly cured concrete often gains more than its design strength; uncured concrete may attain only half its potential. Proper curing also increases wear resistance and durability. Curing should be done as soon as possible without damage to the surface. There are two basic methods: sealing or covering to retain moisture, and adding moisture to keep a continuously high level. Usually only one of these methods is used, but they may be combined where advantageous.
This article discusses liquid membrane-forming compounds, waterproof paper, and plastic sheeting (retaining moisture); wet burlap, cover of wet sand or other nonstaining material and ponding (adding moisture); and colored surfaces. Colored surfaces may be cured by coating with a special curing wax containing the same mineral oxide pigment as used in the dry shake. A clear curing compound or a clean wet curing method may be used. Plastic sheeting or waterproof paper should not be used because achieving complete contact between cover and concrete surface is practically impossible. In areas of contact the color will be darker than in wrinkled areas or other places where the cover is not in contact; the slab generally will not bleach out to a uniform color. Although the same thing can happen in slabs that are not colored, early discoloration of these slabs is usually not objectionable.