Coating defect

Contamination and inclusions

Lumps and rough, peppery spots in the film from dust, spent abrasive, paint skins, fibres or insects. Steel grit in the film rusts through.

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

Causes

Dust and spent abrasive not removed after blasting.
Blasting or sanding nearby while paint is wet.
Slow-drying films in cold weather pick up dirt.

Prevention

Clean the blasted surface and check dust with the ISO 8502-3 tape test.
Keep blasting and painting apart, and strain the paint.

How it is assessed

Visual and by touch; ISO 8502-3 rates dust on the surface before painting. Steel grit in the film is worse than dust: it rusts and stains the coat, so look for rust spots on a new coating.

Telling it apart

Dry spray: Dry spray is an even, sandy texture of paint droplets. Contamination is separate lumps of foreign matter in an otherwise smooth film.
Cratering (fish eyes): Craters are dimples where the paint moved away from oil or silicone. Inclusions are lumps of dirt or grit held inside the film.

Repair

Abrade out the inclusions and recoat the area. The specification and the coating manufacturer have the final word on the repair procedure.

3 practice items in the members area mention contamination and inclusions (CIP 1: 2 · 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.

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.