When resin cures in cold or humid conditions, it can develop a greasy or waxy condition on the surface known as amine blush. The term "amine blush" refers to the reaction between the amines in the hardener and moisture in the air.
Amine blush not only dulls resin's glossy finish but can also prevent additional resin coats from properly adhering if not removed.
How to Identify Amine Blush
Depending on the amount of moisture in the air, amine blush can present as a cloudy, dull appearance or a sticky, greasy, or waxy film on the resin's surface. At times, it may not be immediately visible, but instead of a smooth, glossy finish, you'll notice a drag or resistance when you run your finger along the surface.
The two samples below were made using the same batch of ArtResin.
The first sample was cured indoors in a climate-controlled environment at approximately 78°F/25°C. As expected, it cured perfectly clear, with no surface imperfections. The result is a hard, dry, and smooth surface.
The second sample was cured outdoors, covered, but exposed to intermittent rain during the 24-hour curing period. The temperature ranged from 75-86°F (24-30°C), with outdoor humidity levels between 86-100%. As a result, the resin developed noticeable ripples and waves and experienced amine blush. The surface feels tacky and waxy, with significant resistance when you run your finger along it.
💡 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
Before applying a fresh coat of resin, it’s essential to remove any amine blush. Follow these steps:
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Initial Cleaning: Because the sticky amines are water-soluble, they should wipe away easily and do not require the use of solvents. Amine blush film can clog sandpaper, so start by wiping the resin surface with a soft cloth dampened with warm, soapy water made with a grease-fighting dish soap like Dawn. Repeat if necessary to remove any residue, and wipe clean with plain warm water. Allow the surface to dry and inspect again.
- Persistent Residue: If any film remains, wipe with something more abrasive, such as a Scotch-Brite pad. Allow the surface to dry completely and inspect: the scouring pad will likely have scuffed the resin surface and you will need to apply a fresh coat of resin. Ensure all traces of the blush have been removed prior to sanding.
- Sanding and Reapplying: Wearing a dust mask, use coarse sandpaper to rough up the cured resin surface. Wipe away the sanding debris with a clean, damp cloth. Then, pour a fresh coat of carefully measured and mixed ArtResin to restore clarity. Cover and allow it to cure.
💡 Worried that sanding will ruin your resin coat? Check out our blog Will I See The Scratch Marks From Sanding?
How to Prevent Amine Blush
To prevent amine blush, work with resin only when temperature and humidity are within recommended ranges:
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Maintain Optimal Conditions: Aim for a temperature between 75-80°F (24-30°C) and humidity below 80%, ideally around 50%.
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Use Air Conditioning: Air conditioning reduces humidity and helps maintain a stable environment.
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For Humid Climates: In particularly humid areas, run a dehumidifier for at least a day before working with resin to lower moisture levels.
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Weather Considerations: If air conditioning or a dehumidifier isn’t available, avoid working with resin during rainy or highly humid conditions.
To see the 4 most common ways moisture can get into epoxy resin, please see our blog: How Does Moisture Affect Resin?.
ArtResin: The Original Epoxy For Resin Art.
