When resin cures in humid conditions, it can develop a thin greasy or waxy film on the surface called amine blush.
It forms when moisture in the air reacts with the amines in the hardener.
It can dull the glossy finish and stop new resin layers from adhering properly.
Good news ... it's easy to fix.
What it is
Amine blush is a surface film that forms while epoxy resin cures in cold or humid air.
It typically stays on the surface and doesn't affect the strength of the resin underneath.
When it happens
It shows up when humidity is high during the cure.
More moisture in the air = a higher chance of amine blush.
How to spot it
mine blush can also look or feel like:
- Hazy, cloudy, milky, or dull patches
- A greasy or waxy film
- Tacky spots
- Drag or resistance when you run your finger across the resin surface
- Ripples or waves
- Poor adhesion when you try to recoat
Same Resin. Two Environments:
The two samples below were made using the same batch of ArtResin.
1. Controlled Environment
Indoors with air conditioning and dehumidifier on. Stable temperature of approximately 78°F (25°C) and low humidity.
Result: Smooth, hard, glossy finish. No amine blush.
2. High Humidity Cure
Outdoors during rainy conditions. Temperature between 75-86°F (24-30°C) with 86-100% relative humidity.
Result: Cloudy uneven surface with visible amine blush. Reduced gloss, a tacky feel, and significant resistance when touched. Noticeable surface ripples.
💡 To learn more about curing resin in the heat and humidity of summer, please see our blog How Does Hot Weather Affect Resin?
How to Remove Amine Blush
If you notice amine blush, don't pour a fresh layer over it until it's cleaned. The sticky amines are water-soluble and should wipe away easily (without using solvents).
Step 1: Wash the Surface
- Amine blush film can clog sandpaper, so wipe with a soft cloth dampened with warm, soapy water.
- Use a grease-fighting dish soap like Dawn to help break down the film.
- Repeat if necessary and rinse clean.
- Dry completely and inspect again.
Step 2: If Residue Remains
- Wipe gently with something more abrasive, like a Scotch-Brite pad.
- Rinse again and dry fully.
- Check the surface once dry before moving on.
Step 3: Sand & Recoat (if needed)
The scouring pad will have scuffed the surface and you'll need to apply a fresh coat of resin.
- Ensure all traces of the blush have been removed
- Wear a dust mask and lightly sand the surface
- Remove sanding dust
- Apply a fresh, properly mixed coat of resin
- Don't forget to work in optimal temperature & humidity!
💡 Worried that sanding will ruin your resin coat? Check out our blog Will I See The Scratch Marks From Sanding? For more information on sanding (without ruining your project), see our blog How to Sand Epoxy Resin.
How to prevent it
You can reduce amine blush by working in dry, stable conditions:
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Monitor Temperature & Humidity: Aim for 75-80°F (24-30°C) with relative humidity below 80% (ideally around 50%).
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Use Air Conditioning or a Dehumidifier: This reduces humidity and helps maintain a stable environment.
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Weather Considerations: Avoid curing resin during rainy or humid conditions.
Final Note
Amine blush is a surface issue, not a resin failure, and once you know what it looks like, it's easy to fix and even easier to prevent.
💡 To see the 4 most common ways moisture can get into epoxy resin, please see our blog: How Does Moisture Affect Resin?.
Related Articles:
- Epoxy Resin Troubleshooting
- Why Is My Epoxy Resin Still Sticky?
- How To Harden Sticky Resin
- Why Is My Resin Cloudy? Discover The Main 6 Causes
ArtResin: The Original Epoxy For Resin Art.
