# Steel surface imperfections

Source: https://coatmentor.com/defects/steel-surface-imperfections/ · Updated 2026-10-14

Weld spatter, rough welds, slivers, laminations and sharp edges. Some only appear after blasting removes the mill scale.

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

## Causes

- Welding and cutting.
- Rolling defects in the steel that blasting lifts into slivers.

## Prevention

- Specify a preparation grade for welds and edges (ISO 8501-3, P1 to P3) next to the cleanliness grade.
- Grind spatter, slivers and sharp edges before final blasting.

## How it is assessed

Visual and by touch: a gloved hand snags on slivers. A cleanliness grade such as Sa 2½ alone does not require their removal.

## Telling it apart

- **[Edge corrosion (thin film at edges)](https://coatmentor.com/defects/edge-corrosion/):** Edge corrosion is the result in service. The sharp edge that caused it is an imperfection to fix before coating.
- **[Pinpoint rusting](https://coatmentor.com/defects/pinpoint-rusting/):** Rust spots over the whole surface come from the profile or a thin film. Rust along a weld or a sliver points to the steel itself.

## Repair

Grind or remove the imperfection, reblast the area and stripe coat it. The specification and the coating manufacturer have the final word on the repair procedure.

**17** practice items in the members area mention steel surface imperfections (CIP 1: 10 · CIP 2: 5 · FROSIO written: 2).

## Related

- **Concepts:** [Surface cleanliness grades](https://coatmentor.com/learn/surface-cleanliness/) · [Stripe coats](https://coatmentor.com/learn/stripe-coat/)
- **Standards:** [ISO 8501](https://coatmentor.com/standards/iso-8501/) · [NACE SP0178](https://coatmentor.com/standards/nace-sp0178/)

## 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.