# Undercure

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

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

*Figure: 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](https://coatmentor.com/defects/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](https://coatmentor.com/defects/solvent-entrapment/):** 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).

## Related

- **Concepts:** [Drying, curing and recoat windows](https://coatmentor.com/learn/cure-and-recoat/) · [Pot life and induction time](https://coatmentor.com/learn/pot-life/)
- **Standards:** [ASTM D4752](https://coatmentor.com/standards/astm-d4752/) · [ASTM D2240](https://coatmentor.com/standards/astm-d2240/)

## 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.