Epoxy Amine Blush

Amine Blush can ruin your day

Amine blush is a waxy byproduct of the epoxy chemical reaction that forms onto the surface of the epoxy. This amine blush can inhibit the bonding of subsequent layers of epoxy and other coatings such as primers and paints. Some epoxy formulas will form a blush so thick that you can literally scrape some off with your fingernail. Other epoxies that are sold as “blush free” will have such a small bit of blush that most users will not notice them. But regardless, the builder should assume there is amine blush on every cured epoxy surface especially when making structural bonds in the boat.

The Dangers of Amine Blush

If you have used a lot of epoxy in the past then you probably have your own horror stories about amine blush. Amine blush can hinder the bonding of epoxy laminates by blocking the epoxy bond on the chemical and mechanical level. In the worst of cases the laminate can peel right off of a unprepared surface that had a lot of amine blush on it. In a more moderate case, the amine blush can weaken the bond and the structure will be prone to premature failure. These are the worst situations to avoid and as such special care should be given to any of the structural bonding in your boat because it can affect the structural integrity of the finished craft.

Some other annoying problems that amine blush can cause are a failure for primers and paints to bond , or even cure properly. Amine blush can cause a paint to fish eye, bubble up, never turn glossy, and/or peel off months after you have launched your boat.

Minimizing Amine Blush During Construction

First Line of Defense Make sure you mix the epoxy accurately and work in a dry space. Also, please consider the use of an epoxy system that is blush free/ low blush such as System Three’s Silver Tip epoxy or West System’s 207 hardener.

Peel Ply In a later section Using Peel Ply we will discuss the use of peel ply and its many benefits. The short description is that peel ply will leave a surface that is ready to bond to for most applications even with epoxy systems that are prone to a heavy Amine Blush.

Apply the next Epoxy coat while the Epoxy is still green All epoxies have a green stage where the epoxy is solidified but not fully cured. In this stage, you normally do not need to worry about the amine blush and the new layer of epoxy will form a strong chemical bond to the previous layer. Thus, if at all possible, you should strive to apply the next laminate or coat of epoxy while the previous layer is still green. System Three’s Silver tip resin system has a very long green stage for its epoxy which allows one to recoat in a 1-4 day window depending on the hardener used/ temperature.

Removing Amine Blush and Prepping for Secondary Bonding

Secondary Bonds A secondary bond in composites is any bond that is applied over a fully cured substrate. Secondary bonds are never as strong as a laminate that is cured all at once and thus it is prudent to pay special attention to the preparation of these critical surfaces.

Amine Blush is Water Soluble The best news here is that amine blush is water soluble and thus taking a scrub brush with some warm water will remove even a extreme case of waxy amine blush. If you need to make a secondary bond to a surface that has lots of deep texture that it is unrealistic to sand out, then some water and a scrubby brush will do the trick to remove the amine blush from those deep valleys if you scrub deeply. The one thing ton be aware of is that you need to let the surface dry fully before you apply epoxy over the surface. A secondary benefit to the water solubility of Amine blush is that most water borne paints, varnishes, and primers stick really well to epoxy. For example, many solvent based one part polyurethanes have major compatibility issues with epoxy resin, but their newer waterborne brotheren will stick tenaciously. But always do your research and test samples of new products before you coat a large panel just in case.