What is amine blush?
Amine blush is a waxy bi-product that appears as epoxy cures. It can prevent varnishes and other coatings from bonding. As epoxy cures in contact with moisture, a greasy or waxy film known as amine blush is produced. This film is created on the surface of the cured epoxy. Its appearance alters depending on the amount of moisture in the air, but it’s usually more noticeable in cool, moist conditions. You might struggle to see it at all, or it may appear as a thin, greasy or dull layer.
Why is amine blush a problem?
In itself amine blush isn’t a problem: it’s the effects it causes that are the issue. If you continue working without removing the blush, it will prevent varnishes, further coats of epoxy and other substrates from bonding effectively. Try sanding an amine blush-covered surface and it will clog your sandpaper and cause the blush to penetrate your work more deeply.
Can you prevent amine blush forming?
You can’t stop blush appearing, but by using Peel Ply you can get around the problem – because amine blush forms on the peel ply, not on your cured epoxy. Peel ply is a finely woven nylon fabric that will not bond to epoxy. So simply follow the instructions to apply peel ply to your work; ensure that the peel ply is thoroughly wetted out, let your epoxy cure and then remove the peel ply once cured and before applying the next coating. The blush will have formed on the peel ply, rather than on the epoxy. Once the peel ply is removed, you can carry on with your work as the peel ply’s fine woven pattern is impressed into the epoxy coating, creating a ready to bond to graded textured surface.
Other ways to minimize amine blush
- Avoid ambient and open benchtop curing processes. Curing at 75°F inside an oven is better than curing at 75°F in a lab.
- Cure using a “closed system” technique. Similar to #1, sealing your parts off from ambient humidity, in a box oven, a fume hood, desiccator, a nitrogen dry box or glass bell jar is suggested.
- Avoid fluctuations in ambient temps and humidity, due to monthly or seasonal changes. Curing at 85°F, is better than curing at 77°F; curing at 75°F is better than 70°F.
- Always cure at a temperature above the dew point. When temperatures are below, or close to the dew point, condensation occurs and blush will be more frequent. By curing a few degrees above the dew point, you can avoid sticky cures and an unsightly appearance. A common practice is to go up at least +5°F above the dew point. If this is not possible, fans and heater lamps can be used to prevent moisture interactions upon the epoxy surface.
- Pay attention to small mass curing; less than one gram. Expecting mg amounts of epoxy to be cured properly in your parts is risky, under an ambient cure, since their exothermic nature is reduced. Mixing more mass than needed for your parts is recommended.
- “Fuel” the reaction. “Fueling the exotherm” is a mass favored chemical reaction like gelling and curing. In this step, amineepoxide reactions are forming favorably, instead of amine-moisture unwanted interactions. Allow the mixed epoxy to sit in one container, advancing towards its gel stage. “Staging” the epoxy, is another term used to express this. As a general rule, the shorter the pot-life, the quicker the gel stage, and thus the faster the time to fuel the exotherm.
- Extra potting thickness. In most cases, the epoxy layer in contact with ambient conditions is problematic, whereas the same epoxy is fine at deeper sections, especially towards the bottom of the potting container or mold. One trick is to over-pot, over-mold or over-encapsulate the part. In other words, if a potting thickness of 10mm is required, some processes will use a 12mm mold, where the extra 2mm are removed by mechanical means, such as dicing, cutting, lapping or milling.
How can you get rid of amine blush?
Amine blush is water-soluble, so it’s very simple to clean away. All you need is some warm soapy water and a Scotch Brite pad. Spray the affected surface with the water, wash thoroughly using the pad, wipe dry with paper towels and you’re done. It’s that easy.
Do all epoxies create amine blush?
While slower hardeners such as our 2:1 Epoxy Hardener and our 3:1 Epoxy Hardener, will create less blush than faster-curing epoxies like our 4:1 Hardener, it’s best to assume that some amine blush will form whenever you’re using an amine based epoxy system. After all, it’s extremely straightforward and quick to get rid of, while the alternative – assuming that no blush is present, only to discover that it is after you’ve tried to sand or bond to the surface – can be more painful and a lot more time consuming.