laitance

noun

The milky washings from the surface of concrete which has recently been laid under water.

noun

A weak layer of cement and aggregate fines on a concrete surface that is usually caused by an overwet mixture, overworking the mixture, improper or excessive finishing or combination thereof. Also, could be caused when a slurry mix is used on a deep foundation, where the slurry mix is not completeley removed before placing concrete on top.