Studies have shown that the amount of water needed for cement hydration is always less than that needed for workable. Therefore, effective curing boils down to a matter of providing a moisture barrier to prevent evaporation of the mix water. The several methods of preventing dehydration of concrete vary appreciably in their efficiency and int he time when they can be employed. The following is a short survey of curing methods with a few comments on the characteristics of each type. Most effective of all the known curing materials is water. Most effective, that is, in terms of preventing evaporation of the mix water. In actual practice, use of water by itself as a curing method poses a number of problems. Two curing methods use water as their sole agents: fogging or spraying and ponding. Both of these methods require considerable quantities of water, need careful supervision and are applicable only to horizontal surfaces. For a while burlap was eclipsed by some of the then newly-developed methods- sprayed membranes, plastic sheets, paper, etc.- but in recent years it has made a strong bid for a comeback through a number of improvements. Treatments with plastics, aluminum and other materials have improved its handling qualities, even in cold weather; increased it light reflectance; and curtailed rot. Membrane compounds have become popular curing aids due to their ease of application. When a concrete area is completely sprayed with one of these products it is effectively sealed and evaporation is greatly retarded. Membrane compounds are commonly found in three forms: clear, black, and white. A number of waterproof papers have come on the market in the last decade and found wide use. One of their important advantages is that they do not require periodic additions of water; they assure proper hydration by furnishing a moisture barrier, thereby preventing evaporation. Since water is continuously available, curing proceeds uniformly and the danger of improper curing from a breakdown in water supply is eliminated.