Understanding and Addressing Bubbles in Epoxy Floors

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Epoxy floors have become a popular choice among homeowners and businesses for their durability, attractive look, and easy maintenance. However, like any other flooring solution, epoxy floors can sometimes face issues, with one of the most common being the formation of bubbles or blisters. This article will delve into what causes these bubbles, how they can be prevented, and how to address them should they appear on your floor.

Identifying Bubbles in Epoxy Floors

Bubbles in epoxy floors often manifest as perfect circles, sometimes with a ridge around the edge or appearing as a bubble in the coating. You may or may not see a pinhole at the bottom of the circle, which can be where gas is escaping from the underlying concrete. If no pinhole is present, it indicates that the coating has sealed off the outgassing site. While these bubbles or craters may not look appealing, they typically don’t affect the bond strength of the coating.

Potential Causes of Bubbles in Epoxy Floors

Porous Substrate

The substrate, or the surface where the epoxy is applied, plays a significant role in the formation of bubbles. If the substrate is porous, it can create air pockets that lead to bubble formation. When a high-build epoxy coating is applied, the substrate must be adequately sealed with a primer. If the substrate absorbs the primer, a second coat may be necessary.

Presence of Humidity and Moisture

Moisture in the substrate can also cause bubbles in epoxy floors. As the epoxy reacts with the water, it creates bubbles. It’s essential to apply the epoxy on a dry slab to prevent this issue. Performing moisture tests on the slab can ensure its dryness before the application.

Expansion of the Concrete Slab

The concrete slab’s temperature changes throughout the day can lead to bubble formation. In the early morning, slabs are often more humid and cold. As they warm up later in the day, they expand, and moisture is released into the atmosphere, which can lead to bubble formation. It’s best to apply epoxies around midday, when the slab has already warmed up.

Excessive Solvent

Adding too much solvent to the epoxy mix can lead to bubble formation. While solvents help the product flow better, they evaporate from the screed and leave little pinholes behind. Most bubbles caused by excessive solvent will burst on their own, but some might not. Therefore, if you need to add a solvent, keep it to a minimum.

High-Speed Mixing

Using a high-powered mixer to mix the two parts of an epoxy system quickly can lead to more bubbles. Instead, it’s recommended to use an adjustable speed mixer and mix at a low speed, around 300rpm.

Poor Product Quality

Low-quality products may lack the additives that contribute to defoaming, or they might contain solvents that lead to bubble formation. Always conduct tests first if you’re working with an unknown product.

Improper Bonding

Improper bonding of the epoxy floor system can cause blistering and bubbling. This is often a consequence of inadequate floor preparation. Residue from cleaning agents, previous coatings, or concrete treatments can obstruct the bond between the epoxy and the substrate.

Preventing the Formation of Bubbles in Epoxy Floors

Proper Substrate Preparation

One of the key steps in preventing bubbles in your epoxy floor is proper substrate preparation. This involves ensuring that the substrate is clean, dry, and free of any residues that could hinder the epoxy’s bonding with the substrate.

Controlling Humidity and Moisture

Controlling the humidity and moisture levels in the area where you’re applying the epoxy is another crucial factor in preventing bubble formation. Using a moisture meter to check the moisture levels in the substrate can help ensure that it’s sufficiently dry before applying the epoxy.

Correct Mixing Techniques

Using the correct mixing techniques can also help prevent bubbles. This involves mixing the epoxy at a low speed to avoid whipping air into the mixture and letting the product settle for a few minutes before applying it to the floor.

Choosing Quality Products

Choosing high-quality, solvent-free epoxy products can also help prevent bubble formation. Always conduct tests first if you’re working with an unknown product to avoid any unpleasant surprises.

How to Fix Bubbles in Epoxy Floors

During Primer Installation

If bubbles appear during the primer application, you can use a metal porcupine roller to pop the surface tension as bubbles start to develop. This method can prevent the outgassing bubble from forming and allow the primer to fill in the pinhole that would otherwise be created.

After Primer is Installed

If bubbles appear after the primer has been installed, re-priming the affected area is recommended. In areas where outgassing is particularly aggressive, a viscous epoxy patching material may be required before re-priming.

After Finish Coats are Installed

If the finish coats are applied before the outgassing issue is identified, the best option is to sand the affected areas and patch them with the topcoat material.

Alternative Methods to Get Rid of Bubbles in Epoxy Floors

Using a Hot Air Gun or Blow Dryer

If the resin is still wet when bubbles appear, applying heat can draw the air bubbles to the surface where they can be popped. Use a hot air gun or blow dryer directly above the bubbles, ensuring good ventilation and avoiding the use of flames.

Using a Roller

A metal porcupine roller can be used to pop the surface tension as bubbles start to develop. This method can prevent outgassing bubbles from forming and allow the primer to fill in the pinhole that would otherwise be created.

Using Acetone

Spraying a fine mist of acetone or another denatured alcohol over the surface of an epoxy floor can pop air bubbles, lower the viscosity of the surface, and flatten it out. Denatured alcohol evaporates quickly and doesn’t cause air bubbles to propagate.

Addressing Other Types of Bubbles: Fisheyes and Blisters

In addition to the typical bubbles, other forms of bubbles such as fisheyes and blisters can also occur. Fisheyes are usually caused by residual silicon on the surface, while blisters can contain foul-smelling water rich in minerals due to differences in minerals and chemicals in a liquid. These can be addressed by scrubbing the surface area with medium-grit sandpaper, cleaning the area with a rag dipped in solvent, and applying a fresh coating.

Recoating the Entire Floor

In cases where bubbles appear across the entire epoxy flooring area, it may be necessary to consider shot blasting or sand blasting, which involves removing the epoxy coating by sandblasting the entire area, cleaning the problem area with acid, and then applying the coating again.

Professional Assistance

While this guide provides an overview of how to address bubbles in epoxy floors, it’s essential to remember that professional assistance may be necessary for severe cases. A skilled professional flooring contractor can deliver a beautiful, impressively durable, high-performance floor that meets your expectations, even in the face of outgassing issues.


Understanding what causes bubbles in epoxy floors and how to prevent them is crucial in maintaining the appearance and integrity of your epoxy flooring. While these issues can be frustrating, they are entirely manageable with the right knowledge and techniques. By taking the time to address the issue properly, you can enjoy the benefits of a beautiful, durable epoxy floor for years to come.

 Alex J
Alex J

Alex is the founder of the BFG, he has been in the flooring business for over 12 years and specialize in laying new floors, resurfacing old ones, and giving people practical advice on how to keep their floors looking beautiful.