# Contamination and inclusions

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

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

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

## Related

- **Concepts:** [Surface cleanliness grades](https://coatmentor.com/learn/surface-cleanliness/)
- **Standards:** [ISO 8502](https://coatmentor.com/standards/iso-8502/)

## 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.