Curing is the process of preventing the loss of moisture from the young concrete whilst maintaining a satisfactory temperature regime. The purpose of minimising moisture loss is to achieving a high level of hydration of the cement in the surface layer of the concrete and thus improving durability. As soon as possible, the top surface of the freshly-cast concrete should be covered, for example with a layer of polythene, to prevent drying out. An alternative approach is to cover the surface with wet hessian, but steps must be taken to ensure that this in turn, does not dry out and tend to remove moisture from the concrete. What ever form of protection is used, care must be taken to make sure that the surface of the concrete is not marked; for example, the polythene sheet should be mounted on a timber framework, clear of the surface. As an alternative, liquid curing compounds are available that are sprayed on the surface of the concrete forming a semi-permeable layer.
The sides and soffit of the concrete will be protected initially by the formwork. Once this is removed, the young concrete should be protected as above.
The length of time for which the curing should be maintained will depend on the type of cement used and the ambient conditions. In general it will be in the order of 4 to 6 days. Guidance is given in BS EN 13670 Execution of concrete.
In cold weather it will be necessary to protect the young concrete to prevent moisture in the concrete freezing and hence causing damage.