Concrete Curing
While the water/cement ratio of the concrete mix has a direct impact on the final permeability of a finished slab, the curing of the concrete has an important degree of influence upon the ability of a slab to transmit moisture vapor.
According to American Concrete Institute (ACI) Committee 308 on Curing Concrete, curing is “the maintaining of a satisfactory moisture content and temperature in concrete during its early stages so that desired properties may develop.”
The object of curing is to keep concrete as saturated as possible until the water-filled spaces in the fresh cement paste have been substantially reduced by the filling in of by-products from the hydration of the cement. The best method of curing is by keeping the surface continuously wt for several days by sprinkling or ponding so evaporation is minimized.
The benefits of
curing are many, but in relation to bond of flooring materials, the important
aspect again relates to permeability and the degree to which vapor can move and
affect the flooring bond interface. Besides the problem of not gaining the
desired strength, an improper cure can also result in both crazing and plastic
shrinkage cracks, which are defects that not only allow higher emission levels
to occur, but create sub floor preparation problems for flooring contractors as
well.
Like the water/cement ratio, the cure of concrete has no codes or standards in terms of permeability tolerance for floor surface acceptance. Therefore, those involved on the project should have at least a basic working knowledge of surface quality of the slab in order to recognize obvious defects and potential problems. This is in addition to the vapor emission and alkalinity test data that must be obtained in all installations.