Coating defect

Undercure

A film that stays soft or tacky, dents under a thumbnail, or looks normal but fails in service.

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

Causes

Temperature too low or curing time too short.
Wrong mixing ratio or poor mixing of a two-component coating.
Humidity outside the cure window, for example for ethyl silicate zinc.

Prevention

Power mix complete kits in the supplied ratio.
Keep air and steel within the data sheet's limits until cured.

How it is assessed

Cure tests named in the specification: solvent rub (ASTM D4752 for zinc silicate), hardness, or the maker's test. Being dry to touch is not the same as cured.

Telling it apart

Amine blush: Amine blush is a greasy film on the surface; the film below may be fully cured. Undercure is a film that is soft through its depth.
Solvent entrapment and popping: Trapped solvent also keeps a film soft, but it comes from a coat applied too thick or too soon, not from the cure chemistry.

Repair

Give more time and heat if the maker allows; otherwise remove and reapply. The specification and the coating manufacturer have the final word on the repair procedure.

16 practice items in the members area mention undercure (CIP 1: 6 · CIP 2: 6 · FROSIO written: 4).

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.