Laitance is caused by bleeding of concrete. In case of bleeding, only water accumulates at the top of the surface, but in case of laitance, along with water certain quantity of cement also comes to the surface, forming a thin layer of cement paste at the surface. This formation of cement paste at the surface is known as laitance.
Effects of Laitance on Concrete
If laitance is formed in the construction of concrete pavement, the pavement top surface loses its wearing quality
Laitance formed on road, produces dust in summer and mud in rainy season.
Laitance causes shrinkage cracks.
If laitance is formed on a particular lift, a plane of weakness would form and bond with the next lift would be poor.