Where does the moisture come from?
Free water within the concrete itself is the first source of moisture that challenges a floor covering or coating. To produce concrete of a workable consistency, more water is added to the mixture than that which merely satisfies chemical hydration of the cement. After the slab is placed, finished, and cured, some of this additional water-of-convenience must leave the slab in order for the concrete to reach the moisture requirements of the floor covering, adhesive, or coating. Most manufacturers of flooring materials currently require, before the product is installed, that the moisture emission rate from the concrete not exceed 3.0 pounds, or in some cases 5.0 pounds, of water per 1000 square feet in 24 hours. To understand how challenging it is to comply with these requirements, consider that a 4-inch-thick, 0.50 w/c concrete slab placed at a 4-inch slump can contain between 1600 and 1700 pounds of non-chemically bound water in a 1000-square-foot area. How quickly moisture is lost fro
