# Laitance

Source: https://coatmentor.com/defects/laitance/ · Updated 2026-10-14

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

*Figure: 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](https://coatmentor.com/defects/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)](https://coatmentor.com/defects/bugholes/):** 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).

## Related

- **Concepts:** [Adhesion testing](https://coatmentor.com/learn/adhesion-testing/)
- **Standards:** [ASTM D4258 and D4259](https://coatmentor.com/standards/astm-d4258-d4259/) · [ASTM D7234](https://coatmentor.com/standards/astm-d7234/)

## 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](https://coatmentor.com/method/). CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.