What is Amine Bloom and how is it overcome?

Amine bloom is a surface defect that can occur when epoxy coatings or adhesives cure in the presence of moisture and/or carbon dioxide in the air. It manifests as a greasy or waxy layer on the surface of the cured epoxy. This phenomenon is due to the reaction between the amine hardener in the epoxy and moisture (water vapor) and carbon dioxide in the environment, which forms carbamate compounds on the surface.

Amine bloom typically occurs in mid winter or when it is raining or very high humidity. However it can still occur in warmer temperatures when a sudden change in air and substrate temperature occurs, such as when air conditioning is turned off on a hot day.

Amine bloom creates a layer that can interfere with subsequent coats of paint or epoxy, affecting adhesion.

It can make the surface appear cloudy or greasy, affecting the aesthetic quality of the finish.

1. Amine bloom can be overcome by coating in a controlled environment, for instance by heating and/or dehumidifying. Obviously this isn’t always possible.
2. Accelerating the cure with additives will help reduce the interaction between amines and moisture.
3. There are other additives that can help with amine bloom.
4. Topcoat quickly, before the epoxy primer can react with atmospheric moisture.

The two essential steps are washing with warm water and mild detergent, and sanding thoroughly to gain intercoat adhesion.

N.B. In  some instances, a cured  film can appear normal but the resistance to water spotting has been compromised. In these circumstances the film, even after full cure, can develop white spots when subject to sitting water. The interference of moisture at cure stage has caused a disruption to the correct crosslinking. The epoxy coating is permanently compromised. In this situation mechanical abrading and recoating is required.