without delft green curing coating.. the concrete very obviously cracks allowing vivianite to fill these cracks.
the Delft Green curing coating forms a gel on the surface of wet concrete and protects the concrete by preventing water escaping during the concrete setting reaction. It stops the surface drying out and therefore minimises cracks. If there are even the finest of cracks in the surface of the concrete, during its use water can get in which subsequently expands and contracts with temperature changes and eventually causes the concrete to become damaged.
A Cure for Concrete 