Laitance
A weak layer of cement fines and water drawn to the concrete surface by bleeding or overworking. It has almost no strength and bonds poorly to anything.
What does laitance mean?
Laitance forms naturally as fine particles rise with bleed water, and finishing operations performed too early work it back into the surface. The resulting layer dusts under traffic and causes bond failure for overlays, coatings, and toppings. Removal by grinding, shot blasting, or acid etching is standard preparation before any bonded material is applied.
In practice
When an epoxy garage coating peels off in sheets with concrete dust on the back, laitance was left in place.