Coating defect

Bugholes (surface voids in concrete)

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

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: Laitance is a weak skin over the whole surface. Bugholes are separate voids, many hidden under a thin crust.
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).

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.

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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.