What is 'laitance' and why remove it?

Laitance is a weak, milky layer of cement dust and fine aggregates that rises to the surface of over-wet concrete or during troweling. It has very poor structural strength. If you apply a coating or repair mortar directly over laitance, the coating will bond to the laitance, which will then peel away from the main slab. We always remove laitance via grinding or shot blasting to expose the sound aggregate beneath before applying any flooring or waterproofing system.