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What is epoxy amine blush and what is its effect on polyurethane products?

What is amine blush?

When using a solvent free epoxy resin such as SureFloor UVS Clear Epoxy, there are some factors you should consider before over coating with a polyurethane. 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 it is 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?

Con-Treat recommends thoroughly washing the cured epoxy with a 50/50 blend of clean water & methylated spirits. 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 or two part polyurethane such as Fortis 519 and do not remove the amine blush, the blush will migrate through to the top of the surface causing the polyurethane finish to improperly cure from the contaminated areas. Some epoxy resins can take up to 2 weeks to fully cure, still releasing amine blush to the surface. In summary, always remove surface contamination, including amine blush, to avoid any problems with adhesion, drying or discolouring. After washing the epoxy surface, leave to dry prior to applying subsequent coatings.

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