What is amine blush and what is its effect on single-pack products?

What is amine blush?

When using a solvent free epoxy resin such as Interlux Epiglass® Epoxy Resin HT9000, there are some factors you should consider before overcoating with a primer. After application and during the curing (drying) process, the epoxy releases a blush to the surface called ‘Amine Blush’. This blush is known to appear as a ‘wax-like’ film that sits on the surface of the cured epoxy resin. This amine blush will in fact keep some subsequent products applied from fully curing, performing correctly and also yellowing unless removed properly. The visibility of the blush will be determined by the moisture in the air during the curing process, however will still be on the surface if not always visible. The best way to reduce blushing is to work in warm temperatures (the epoxy sets up fast, reducing the blush window) and with humidity at low levels. It would be best to avoid conditions where moisture is coming out of the air as temperatures fall.

How to remove it?

Interlux recommends thoroughly washing the cured epoxy with clean warm water, all-purpose soap, and a stiff brush or Scotch-Brite™ pad. The amine blush is water soluble therefore the only way to completely remove this is by following the instructions above. You will want to clean the amine blush off of the epoxy before sanding as well. If you begin to sand before removing the amine blush, you may sand the blush deeper into the surface making it much harder to remove. It is a safe practice to clean all types of epoxy resin, even if the label states that it is ‘amine blush free’ or ‘no blush formula’. Please note: Aggressive solvents like Acetone will not remove the blush.

What will it do to my project?

If amine blush is present on the surface and is not properly removed, you might not notice a problem with your project until after it is completed. If you use a single-part primer such as Interlux Pre-Kote and do not remove the amine blush, the blush will migrate through the Pre-Kote to the top of the surface causing the Brightside® single-part polyurethane finish to improperly cure from the contaminated areas. It could also lead to detachment of both primer and finish. For a more robust solution, Interlux recommends a two-part primer such as Epoxy Primekote® Y404KIT to seal the amine blush from penetrating through the coating. Some epoxy resins can take up to 2 weeks to fully cure, still releasing amine blush to the surface. Epoxy Primekote® Y404KIT will keep that new amine blush from penetrating through the coating to the top of the surface. However, this doesn’t mean you do not have to remove the amine blush from the epoxy resin before applying Y404KIT. If the blush is present, as you roll or brush the Epoxy Primekote® Y404KIT over the cured epoxy resin (with blush on the surface) the amine blush can mix into the Y404KIT as it is being applied causing that blush to sit at the top of the surface. When applying Perfection® to a surface with amine blush on the area, the Perfection in certain colors can also ‘yellow’ prematurely. In summary, always remove surface contamination, including amine blush, to avoid any problems with adhesion, drying or discoloring. After washing the epoxy surface, leave to dry prior to applying subsequent coatings.