# Bugholes (surface voids in concrete)

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

Small pits in formed concrete, usually up to about 15 mm across, many hidden under a thin crust of mortar.

*Figure: Bugholes (surface voids in concrete): the surface as you see it, and a schematic cross-section.*

## Causes

- Air bubbles and water trapped against the formwork when the concrete is placed and vibrated.

## Prevention

- Good vibration and suitable form release agents when the concrete is cast.
- Fill the voids before a thin coating, so that air in them cannot rise into the wet film.

## How it is assessed

Visual after surface preparation, which breaks the crust and opens hidden voids.

## Telling it apart

- **[Laitance](https://coatmentor.com/defects/laitance/):** Laitance is a weak skin over the whole surface. Bugholes are separate voids, many hidden under a thin crust.
- **[Outgassing](https://coatmentor.com/defects/outgassing/):** Bugholes are voids in the concrete before coating. Outgassing is bubbles and pinholes that form in the coating when air leaves the voids as the concrete warms.

## Repair

Prepare the surface first, then fill the voids with a surfacer or filler before a thin or immersion coating. The specification and the coating manufacturer have the final word on the repair procedure.

**1** practice item in the members area mentions bugholes (CIP 2: 1).

## Related

- **Concepts:** [Holiday (discontinuity) testing](https://coatmentor.com/learn/holiday-testing/)
- **Standards:** [ASTM D4258 and D4259](https://coatmentor.com/standards/astm-d4258-d4259/) · [NACE SP0892](https://coatmentor.com/standards/nace-sp0892/)

## 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.