# Cathodic disbondment

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

The coating loses adhesion and lifts, as blisters or larger areas, around a holiday on a buried or submerged structure under cathodic protection.

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

## Causes

- Cathodic protection current at a holiday makes the steel surface alkaline and can make hydrogen, which push the coating off.
- Coatings that alkali attacks, such as alkyds, used with cathodic protection.
- Holidays and damage left in service.

## Prevention

- Use coatings tested for cathodic disbondment, such as fusion-bonded epoxy, multi-layer polyolefin or suitable liquid epoxies.
- Keep cathodic protection within its criteria and repair damage.

## How it is assessed

In the laboratory by cathodic disbondment tests; in the field by inspection and adhesion checks round holidays. ASTM G8 is the laboratory test for cathodic disbondment of coated steel; it replaced ASTM G95.

## Telling it apart

- **[Undercutting (underfilm corrosion)](https://coatmentor.com/defects/undercutting/):** Undercutting is rust creeping under the film from a defect. Cathodic disbondment is a loss of adhesion driven by the protection current round a holiday. Once lifted, the coating can shield the steel from that current.
- **[Blistering](https://coatmentor.com/defects/blistering/):** Blisters from salts or solvent can form anywhere. Cathodic disbondment grows round holidays on a protected structure.

## Repair

Remove the disbonded coating to a sound edge and repair with a compatible coating. The specification and the coating manufacturer have the final word on the repair procedure.

**16** practice items in the members area mention cathodic disbondment (CIP 1: 4 · CIP 2: 10 · FROSIO written: 2).

## Related

- **Concepts:** [Cathodic protection basics](https://coatmentor.com/learn/cathodic-protection/) · [Holiday (discontinuity) testing](https://coatmentor.com/learn/holiday-testing/)
- **Standards:** [ISO 15589-1](https://coatmentor.com/standards/iso-15589-1/) · [ISO 12944-9](https://coatmentor.com/standards/iso-12944-9/)

## 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.