Coating defect

Laitance

A thin, weak, powdery layer of cement and fines on the top of concrete, sometimes with fine crazing.

Laitance: the surface as you see it, and a schematic cross-section.

Causes

Water bleeding to the surface of wet concrete.
Overworking or over-troweling the surface.

Prevention

Avoid excess water and over-troweling, and cure the concrete properly.

How it is assessed

A pull-off test that breaks just below the coating, with a thin skin of concrete on the dolly, points to laitance. Any coating is only as strong as the surface under it, so a weak top layer must go before coating, however clean it looks.

Telling it apart

Efflorescence: Efflorescence is salt crystals brought to the surface later by water. Laitance is weak cement paste from the casting itself.
Bugholes (surface voids in concrete): Bugholes are separate pits in formed faces. Laitance is a weak skin over the whole top surface.

Repair

Remove laitance by abrasive blasting, grinding or waterjetting (ASTM D4259); cleaning alone does not remove it. The specification and the coating manufacturer have the final word on the repair procedure.

7 practice items in the members area mention laitance (CIP 2: 6 · FROSIO written: 1).

Try it in an exam-style question. The free readiness check shows the question style, explains every answer and gives you a dated study plan.

Take the free readiness check See the tracks

About this page

Written from coating practice and the published rating standards, in our own words; the drawing is schematic. Checked on 2026-10-14; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.