Coating defect

Fading and discoloration

A paler, washed-out or yellowed surface, often with a loss of gloss.

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

Causes

Ultraviolet light breaks down pigments that are not light-stable and aromatic binders such as epoxies.
Heat, moisture and chemicals in the air.

Prevention

Use a UV-stable top coat, such as an aliphatic polyurethane or polysiloxane, over epoxy outdoors.

How it is assessed

Compare with a colour standard. Rub a little oil on the surface: chalked film darkens again, while true pigment fading does not.

Telling it apart

Chalking: Chalk is loose powder on the surface and wipes off on a cloth. Fading is a change in the film itself and does not wipe off.
Bleeding: Bleeding brings colour up from the coat below, often over old coating or patches. Fading makes the colour paler or yellow over the whole exposed face, worst where the sun falls.

Repair

Wash, abrade lightly and overcoat with a weather-resistant top coat. The specification and the coating manufacturer have the final word on the repair procedure.

3 practice items in the members area mention fading and discoloration (CIP 1: 1 · CIP 2: 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.