What amine blush is
While an epoxy cures, unreacted amine at the surface can react with carbon dioxide and moisture in the air instead of with the resin, forming ammonium carbamates and carbonates. These salts sit on the surface as a greasy, waxy or hazy film, sometimes with white streaks or a sticky feel. Closely related amine bloom or “sweating” describes amine migrating to the surface without fully reacting.
Why it happens
- Low temperature slows the epoxy–amine reaction, giving amines more time to meet CO₂ and water.
- High humidity or condensation, especially when the surface is near the dew point.
- Combustion heaters (propane, kerosene) that pump CO₂ and water vapor into the space.
- Reactive, low-molecular-weight amines such as unmodified aliphatic polyamines.
- Short or skipped induction time when the product calls for it.
How to prevent it
- Keep substrate and air within the product’s temperature limits and the surface at least 3 °C (5 °F) above the dew point.
- Use indirect-fired or electric heat rather than direct combustion heaters.
- Provide gentle air movement without blowing dust onto the film.
- Follow the induction (sweat-in) time where the data sheet specifies one.
- Choose blush-resistant hardeners such as adducts, cycloaliphatic amines or phenalkamines for cold or damp work.
How to remove it
Blush is water-soluble. Scrub with warm water (a mild detergent can help), rinse thoroughly and let the surface dry before recoating. Solvent wiping alone tends to smear it rather than remove it. If the recoat window has passed, abrade after washing.
Quick checkIf water beads or the surface feels greasy, or a damp cloth leaves a film, wash before topcoating. Blush trapped between coats is a classic cause of delamination.