Coating defect

Solvent entrapment and popping

Bubbles, blisters or small craters in the film, and a film that stays soft. Popping is air or solvent bursting through the surface.

Solvent entrapment and popping: the surface as you see it, and a schematic cross-section.

Causes

Film far above the maximum DFT: the surface skins over and traps solvent below.
A full wet coat over a porous primer such as inorganic zinc without a mist coat.
Overcoating before the minimum recoat time.

Prevention

Keep DFT within the specified range.
Use a mist coat over porous primers; respect recoat times.

How it is assessed

Visual inspection. Check hardness and DFT. Trapped solvent can later cause blistering in service. Note: ISO 19840 is for CIP 2 and FROSIO only.

Repair

Remove soft or bubbled coating and reapply correctly; minor surface popping may be abraded and overcoated if the spec allows. The specification and the coating manufacturer have the final word on the repair procedure.

6 practice items in the members area mention solvent entrapment and popping (CIP 1: 1 · FROSIO written: 5).

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 2026-10-04; 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.