What is Amine blush
Amine blush is a normal chemical reaction between amine-curing agents and carbon dioxide when in the presence of moisture, forming a carbonate which appears as a greasy film on the surface.
Causes of Amine blush
The main contributing factors of Amine blush are
1) High humidity.
2) The presence of excess carbon dioxide in the atmosphere.
3) Low curing temperature.
4) Improper and inadequate mixing of the resin and hardener.
How can amine blush be detected?
Amine blush is best detected by lightly rubbing the surface to detect a greasy or waxy film or to see the visual effect on the surface. The surface may have a lower gloss, oily or greasy film, haziness, slight yellowish or whitish tint or a patchy appearance when viewed at different angles. It can appear as greasy white spotting or even salt-like crystalline deposits.
What does it cause?
- Imperfections in the coating surface
- Compromised cleanability
- Decreased stain resistance
- Surface tackiness
- Loss of gloss
- Poor adhesion
- Difficulty in re-coating
- Faster yellowing
How can amine blush be prevented?
In general, most epoxies can be subject to blushing under certain conditions, however some epoxy coatings are more prone to blushing than others. The following precautions should be taken:
- After mixing, adhere to all the recommended induction or “sweat in” times in the product literature.
- Avoid sources of direct combustion such as direct-fired heaters, forklift trucks, welding equipment and combustion engines.
- Ensure coating products are stored in warm conditions (i.e. room temperature or slightly warmer).
- Check the environmental conditions and apply materials when the temperature is a minimum of 50F above dew point and rising. Do not use propane heat in closed environments because they emit CO2.
Amine blush should be removed at the first stage it presents itself, otherwise it can prevent effective bonding between the substrate or with further coats of epoxy.