# Pinpoint rusting

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

Many tiny rust spots spread over the surface, often soon after coating.

*Figure: Pinpoint rusting: the surface as you see it, and a schematic cross-section.*

## Causes

- Profile peaks standing above the film or covered too thinly: the profile was too high for the DFT.
- Film too thin overall.
- Flash rust or contamination on the peaks before priming.

## Prevention

- Keep the profile within the specified maximum.
- Make sure the first coat covers the peaks; measure DFT over the profile correctly.

## How it is assessed

Record the distribution as pinpoint rusting (ASTM D610 type P) and rate the area; check profile and DFT on nearby areas.

## Telling it apart

- **[Rust-through (rusting)](https://coatmentor.com/defects/rust-through/):** General rust-through is the end of the coating's life over larger areas. Pinpoint rusting is many tiny spots, often soon after coating.
- **[Contamination and inclusions](https://coatmentor.com/defects/contamination/):** Steel grit caught in the film also rusts as small spots, but it shows as lumps you can feel.

## Repair

Usually abrade or reblast, then recoat to the correct DFT; the extent sets the method. The specification and the coating manufacturer have the final word on the repair procedure.

**5** practice items in the members area mention pinpoint rusting (CIP 2: 3 · FROSIO written: 2).

## Related

- **Concepts:** [Surface profile (anchor pattern)](https://coatmentor.com/learn/surface-profile/) · [Dry film thickness measurement](https://coatmentor.com/learn/dft-measurement/)
- **Standards:** [ASTM D610](https://coatmentor.com/standards/astm-d610/) · [ASTM D4417](https://coatmentor.com/standards/astm-d4417/)

## 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.