What causes bubbles in an epoxy floor and how do you fix them?

Bubbles in an epoxy floor almost always come from one of four things: air escaping from the concrete, air whipped into the mix, a hot slab or room, or skipping the defoaming roller. The fix depends on timing. Wet bubbles get rolled out right away; cured bubbles and pinholes get sanded, cleaned and touched up with more kit material.

Here is what causes them, how to stop them before they start, and what to do if your floor already has them.

Where the bubbles come from

1. Outgassing from the concrete

Concrete is full of tiny pores, and those pores hold air. As the coating goes on, the slab releases that air up into the wet epoxy. This is normal and it happens on nearly every job. It is the main reason our installation guide tells you to defoam every section right after you spread it. Porous or older concrete releases more air, which is one reason we strongly recommend primer on those floors. A thin, tack free primer coat gives the epoxy a sealed surface to sit on.

2. Over mixing or mixing the wrong way

The kit needs a drill and mixing paddle for 3 to 5 minutes, scraping the sides and bottom of the bucket. That is enough. Running the drill much longer, running it at high speed, or letting the paddle ride up near the surface folds air into the material. Keep the paddle low in the bucket and the speed moderate. Do not switch to hand mixing to avoid bubbles; hand mixing leaves soft spots, which is a bigger problem. Mix one kit at a time so each batch gets the same treatment.

3. Heat

Hot conditions add bubbles. A warm slab pushes more air out of the concrete, and above 75°F the pot life gets shorter, so you have less time to defoam before the coating starts to firm up. Above 85°F, work in smaller batches. In Arizona that usually means starting early in the morning while the garage is still cool, with the door closed against direct afternoon sun. Stay inside the 41°F to 90°F application window and keep relative humidity below 65%.

4. Skipping or rushing the defoaming roller

This is the big one. The spiked 20 inch defoaming roller breaks the bubbles that rise to the surface so the self leveling coating can flow back over the spot. Skip it, and those bubbles cure as pinholes and craters. Rush it, and you leave bubbles behind. The guide calls for 2 to 3 slow passes over each area with 50% overlap, while the coating is still wet.

How to prevent bubbles on your pour

1. Prep the slab fully. Clean, degrease, grind to a texture like 60 grit sandpaper, and vacuum every bit of dust. See our post on grinding, acid etching or resurfacing for why grinding matters.
2. Moisture test first. Do the moisture test before you start, and do not coat when humidity is at or above 65%.
3. Prime porous or older concrete. Primer is sold separately. Apply it thin, do not puddle it, and wait until it is tack free.
4. Pick a cool part of the day. Ideal cure temperature is 68°F to 77°F. Hotter than that, work smaller batches.
5. Have tools ready before you open a bucket. You get 20 to 30 minutes of working time once mixing begins. Squeegee, roller, extension pole and spiked shoes should all be in reach.
6. Mix right. Drill and paddle, 3 to 5 minutes, scrape the bucket, one kit at a time.
7. Spread at full thickness. Use the full 100 sq ft per kit. A thin coat does not level well, and bubbles have less material to close over. Not sure how many kits you need? Read how many epoxy kits do I need.
8. Defoam every section immediately. Spread a 100 to 150 sq ft section with the 22 inch squeegee, distribute the quartz aggregate, then roll it 2 to 3 times, slowly, with 50% overlap.
9. Do not aim fans or heaters at the floor. Ventilate the space, but keep air and heat off the surface during cure.

How to fix bubbles that are still wet

If you spot bubbles while the coating is still flowing and you are inside the pot life, roll the area again with the defoaming roller. Go slowly and overlap your passes. Once the coating starts to firm up, stop. Rolling partly set epoxy drags the surface and leaves marks that are harder to fix than a few pinholes. Let it cure and repair later.

How to fix cured bubbles and pinholes

Wait until the floor has fully cured. Full cure is 72 hours. Then pick the repair that matches how bad it is.

A few bubbles or pinholes

1. Sand each spot smooth and dull so the new material has something to grip.
2. Vacuum the dust and wipe the area clean. Dust left behind acts as a barrier.
3. Touch up with additional kit material, mixed at the ratio on the label with a drill and paddle. Mix only what you need.
4. Let it cure before traffic: 24 hours for light foot traffic, 72 hours for full cure.

Bubbles and craters across the whole floor

When the problem is widespread, spot repairs will look patchy. The better fix is a fresh coat. Clean the floor, abrade the entire surface, vacuum all the dust, and apply a new coat over the existing layer. You do not need to remove the old coating as long as it is well bonded. Plan the same kit count you used the first time, since each kit covers 100 sq ft. Our post on putting a second coat of epoxy on a garage floor walks through it.

If you are seeing bubbles alongside other problems, like soft spots or peeling, read what can go wrong with an epoxy floor. Those usually point to prep, mixing or temperature, and they need to be fixed before you recoat.

When to call us

Call before you sand anything if you see any of these:

• Craters over most of the floor, or bubbles that keep showing up in the same areas
• Bubbles together with peeling or lifting edges
• A floor that is still tacky after 48 hours, or anything still tacky at 72 hours
• You are planning a second coat and want to confirm prep and kit count

Every kit comes with free phone support, Monday to Friday, 8am to 5pm Arizona time. Planning a job near you? Our city planning guides cover local conditions and pickup in the Phoenix area.

Quick answers

Why does my new epoxy floor have tiny pinholes?

Pinholes are bubbles that popped or rose after the defoaming pass and then cured open. They usually come from air leaving the concrete, a missed or rushed defoaming roller pass, or a hot slab.

Can I pop bubbles after the epoxy starts to set?

Only while the coating is still wet and inside the 20 to 30 minute pot life. Once it starts to firm up, rolling will drag and mark the surface. Let it cure and repair the spots afterward.

How do I fix a few cured bubbles?

Sand the spot smooth, vacuum and wipe it clean, then touch it up with additional kit material. Small touch ups blend well when the area is clean and dull before you apply.

What if the whole floor is covered in craters?

Clean and abrade the entire surface, then apply a fresh coat over the existing layer. You do not need to remove the old coating as long as it is well bonded. Call us at 602.600.0781 before you start so we can help you plan it.