Coating defect

Cathodic disbondment

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

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): 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: 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).

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.