What’s Causing My Terrazzo to Bubble?

Frederick M Hueston  StoneForensics.com

If you’ve ever walked into a room and noticed bubbles or blisters on a terrazzo floor, you’ve probably scratched your head wondering what went wrong. Well, you’re not alone—it’s a common issue with epoxy terrazzo, but the culprit isn’t what most people think. Spoiler alert: it’s not the chemical stripper you used. Let’s get to the bottom of it.

Osmotic Pressure: The Real Villain

The number one cause of bubbling or blistering in epoxy terrazzo is osmotic pressure. Picture this: moisture from beneath the concrete slab is trying to work its way up. When it hits the non-porous epoxy layer, it gets trapped and starts to build pressure. Over time, that pressure causes the epoxy layer to lift, creating those unsightly bubbles.

This often happens when the concrete slab wasn’t properly moisture-tested or sealed before the terrazzo was installed. Even a small amount of moisture seeping upward can wreak havoc, especially if the underlying surface wasn’t prepped with a moisture barrier.

Let’s Clear the Air About Chemical Strippers

Now, I know what you’re thinking: “Did that strong chemical stripper cause the problem?” The answer is no. Epoxy is highly chemical-resistant—that’s one of its best features. It’s designed to stand up to harsh cleaners, chemical spills, and yes, even strong strippers. When you’re stripping a coating or sealer off an epoxy terrazzo floor, the stripper is only affecting that top layer of finish or coating, not the epoxy base itself.

Stripping the Coating: No Harm, No Foul

Stripping an old finish off an epoxy terrazzo floor is a normal part of maintenance and refinishing. As long as you’re using the right tools and products, you’re not going to damage the epoxy. Follow these tips to make sure the process goes smoothly:

Choose the Right Stripper: Use a product designed for the type of finish or coating you’re removing.

Follow Dwell Times: Give the stripper enough time to work, but don’t let it dry out.

Rinse Thoroughly: After stripping, rinse the floor with clean water to neutralize any remaining chemical residue.

The epoxy layer underneath is tough—it won’t be affected by a proper stripping process.

Fixing the Bubbles

Unfortunately, if you’re dealing with bubbles caused by osmotic pressure, a simple recoat won’t fix the issue. Here’s what you’ll need to do:

Test for Moisture: Use a moisture meter to check the moisture levels in the concrete substrate.

Remove the Bubbled Epoxy: Sand down the bubbled areas and remove the damaged sections.

Apply a Moisture Barrier: If moisture is detected, apply a moisture mitigation barrier to stop the water from coming up.

Recoat with Epoxy: Once the moisture issue is resolved, reapply the epoxy and finish with a topcoat.

Prevention is Key

To avoid bubbles in the future, make sure the concrete slab is tested and prepped before installation. A good moisture barrier can make all the difference and save you from costly repairs down the line.

If your terrazzo floor is bubbling, don’t blame the chemical stripper—it’s not the bad guy in this story. The real problem is likely moisture trapped under the surface. Once you address that, your epoxy terrazzo floor will be back to its smooth, beautiful self. So, strip away those old coatings with confidence—your epoxy can take it.

And as I always say, the stone (or terrazzo) never lies. You just have to know how to read the clues.