What is laitance and how can it affect finishing?

• A. Laitance is a dense, cement-rich surface layer that strengthens finishing
• B. Laitance is a weak, cement-rich surface layer that can cause dusting, pitting, and poor adhesion if not removed or covered by proper finishing and curing
• C. Laitance is a color variation on the concrete surface
• D. Laitance is a type of air void that improves finish texture

Answer: (B)

Laitance is a weak, cement-rich surface layer that forms on top of fresh concrete as bleed water brings fine cement to the surface. Because this layer is not well bonded and lacks strength, it tends to dust off and can reveal a rough, crumbly, or chalky finish. If laitance remains, finishes, coatings, or toppings won’t adhere properly, leading to peeling, flaking, or a pitted, uneven surface. To prevent or fix it, remove the laitance before finishing (mechanical methods like grinding or shot blasting, or thorough washing/etching), and ensure proper curing and adequate time for bleed water to evaporate. This keeps the surface solid and ready for coatings and other finishes, improving adhesion and overall durability.