Coating defect

Peeling

The film lifts in larger, flexible sheets or strips, often from edges, seams or penetrations.

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

Causes

Poor surface preparation or a contaminated surface.
Contamination between coats, or a coat applied after its recoat window.
Alkyd paint on galvanizing: the zinc saponifies the binder and leaves a soapy layer.

Prevention

Prepare and clean the surface as specified.
Use coatings suited to the substrate, for example no alkyd directly on zinc.

How it is assessed

Visual, with adhesion tests round the area. Peeling is in soft, pliable films; flaking is in hard, brittle ones.

Telling it apart

Flaking and delamination: Flaking breaks hard, brittle films into small chips. Peeling lifts soft, pliable films in sheets.
Delamination (intercoat adhesion failure): When a coat parts cleanly from the coat below, the defect is an intercoat failure. Peeling is the wider term for a film that comes off in sheets.

Repair

Remove all loose coating to a sound edge, find and correct the cause, then prepare and recoat. The specification and the coating manufacturer have the final word on the repair procedure.

9 practice items in the members area mention peeling (CIP 1: 3 · FROSIO written: 6).

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.