Osmotic Blisters: The Plague of Resin Floors

For decades, builders and owners have chosen resin floors for their seamless strength. When the base resin is mixed with a reactive hardener, the two react and cure in place.

Although manufacturers use different chemistries to make resin floors, this curing reaction is critical to how they form.

High School Chemistry: Osmosis

In osmosis, water moves through a semi-permeable membrane from a more dilute solution toward a more concentrated one. The membrane lets water pass but blocks the dissolved substances, so the concentrations can never even out, and water keeps moving toward the concentrated side.

In a resin floor, the coating itself (or the bond line between the coating and the concrete) can act as that semi-permeable membrane. If water-soluble material is trapped under the coating, moisture from the concrete moves toward it. As water collects in that pocket, the pressure can eventually exceed the coating’s bond to the concrete and push the coating up into a blister.

Think of the concrete as one slice of bread and the resin floor as the other. If something soluble is trapped between the slices, moisture from the bottom slice keeps flowing toward it until the top slice lifts.

“What Happened?”

Osmotic blisters are a contractor’s nightmare for two reasons. First (and obviously), they can ruin otherwise good work. Second, too many installers put down resin floors without understanding how much moisture contributes to osmotic blisters.

Apply a resin floor over a concrete slab that still holds too much moisture, and you invite blisters. To prevent them, you first need to understand what causes them.

Free Download – 4 Reasons Why Your Concrete Is Taking Forever to Dry

The Ingredients of Osmotic Blisters

1. A semi-permeable membrane: usually the coating itself or the bond interface between the coating and the concrete.
2. Concentrated water-soluble material (organic or inorganic): the wild card. It can come from resin ingredients in the epoxy coating, residue from acid etching, concrete admixtures, or soluble salts in the concrete.
3. Water: moisture in the slab, whether it’s left over from the concrete mix or coming up from the ground below.

The Natural Cure

There’s no simple test that predicts osmotic blisters. However, relative humidity (RH) testing gives installers essential data on concrete readiness. If the slab’s RH is higher than the flooring or coating manufacturer allows, hold off on installing the resin floor.

Preemptive Measures

• Try to minimize the amount of soluble salts in the concrete mix design.
• Install a water vapor retarder beneath the slab.
• Avoid acid etching as surface preparation for a coating application.
• Check that the epoxy coating’s components are accurately proportioned and properly mixed.
• Check the slab’s RH during curing and drying to make sure it’s ready.

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Jason Spangler

Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.

Last updated on October 14th, 2026