In this article I want to share with you one of my big fears when it comes to resinous floors: Transparent top-coats. Over the years I have had some traumatizing experiences with clear coats and as a result I am always very cautious to specify them.
Clear epoxy coatings are usually applied as an additional protection layer on top of an epoxy or polyurethane floor. They can serve several purposes such as scratch resistance, protecting flakes and other aggregates, as well as general protection from dirt pick up.
Clear-coats (and all types of varnishes for that matter) are not easy to apply, and beware of sales reps claiming otherwise!
I still remember the first time that I specified a clear coat. We had just applied a beautiful white glossy epoxy floor. As we moved on to apply the topcoat I was naïve enough to believe that you simply slap the clear coat on top of the existing floor with a roller and then we all go home satisfied.
Surface Tension in epoxy coatings
But as we were finishing up we started noticing little craters opening up (fish eyes) all over the floor. That’s when I got my first lesson in surface tension. The base was a smooth glossy substrate that wasn’t the most welcoming surface for the clear topcoat to be added on top. The new coat was not able to ‘wet’ the surface sufficiently. It turns out that that epoxy top coats are notorious for their rather high surface tension. The lesson that we learnt was to always make sure that the surface tension of the clear coat is lower than that of the base coat. When coating over rough (or sanded) surfaces this shouldn’t be a problem, but smooth glossy surfaces can cause issues.
We then tried to fix the wetting problem by adding some extra solvent to the product (and thus making the product thinner). We managed to eliminate the fish eyes problem… but instead we got bubbles… Lots of them… No matter what application technique we tried (paint rollers, spiked rollers, brushing, back rolling) them bubbles kept on coming back. It turns out that we had gone overboard on the solvent. And as the solvent evaporated, gas was being generated within the coat.
Our next option was to apply a thicker clear coat build. By applying more product on to the surface we could reduce the risk of fisheyes occurring without needing to add solvent. The result looked great … We got this beautiful smooth glassy looking surface… However on the next day we noticed some surface defects. There were no fisheyes, no bubbles, but instead we got hazy patches on the floor. It turns out epoxy does have a tendency to lose its clear colour once it exceeds a few mm in thickness. As the resin had been applied on the floor some areas had a slightly thicker build and this led to hazy patches.
I am not telling the above stories to scare any of you readers away from working with clear coats. I have seen some amazing projects completed over the years with clear coats. But I really feel that this is an area of the industry that no one is talking about, and as a result many projects are failing simply because of a lack of knowledge.
What are your experiences with epoxy clear coatings? Please let me know!
Akis Apostolopoulos
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