Why Is My Epoxy Floor Turning White?
Troubleshooting
White on an epoxy floor is almost always water telling you where it is. The important question is which side of the coating it is on. A haze sitting on top of the film is usually a surface reaction from the day it cured and it washes or abrades off. A white bloom underneath the film is moisture coming up through the slab, and that one does not wash off, does not improve with a topcoat, and generally ends with the floor coming up. Working out which you have takes about two minutes.
General guidance, not a diagnosis of your floor · Authorized dealer for every brand we carry · Counter in Pompano Beach · We speak English, Spanish and Portuguese
The two minute test
Is the white on top or underneath?
Wet a small area with clean water and wipe it. Then scuff a patch lightly with a fine abrasive pad and wipe it clean.
It disappears when wet, comes back when dry
The white is on the surface. Light refraction off a hazed or chalked top layer. Water fills the texture and the haze vanishes. This is good news and it is nearly always repairable.
It comes off on the pad
Surface residue: amine blush, efflorescence carried up and deposited on top, or a cleaning film. Also good news. It washes and abrades away.
Nothing changes
The white is inside or under the film. This is moisture between the coating and the concrete, and the coating is losing its bond where you see it. This is the serious one.
Confirm it by cutting into a white area with a sharp blade and lifting a small piece. If the underside of the coating is white, chalky or damp, the slab is driving moisture into the bond line.
Causes, most common first
Why it happened
1. Moisture vapor coming up through the slab
The most common serious cause, and in South Florida the default suspect. Concrete on grade carries water vapor upward continuously. Coat over a slab with high vapor drive and no barrier, and water collects at the bond line, where it whitens the underside of the film, carries dissolved salts with it and progressively breaks the bond. Left alone it becomes blistering and then peeling.
This is why the moisture test is not optional. The three tests worth running take an afternoon and they are the difference between a floor and a second floor. What a moisture vapor barrier does covers the fix.
2. Amine blush
Humidity reacting with the hardener at the surface during cure. It leaves a waxy, hazy, sometimes greasy film on top of a coating that is perfectly cured underneath. Very common on evening pours when the temperature is falling and the dew point is close, which describes a lot of Florida days. It washes off with water and a scrub pad.
3. Water that got onto the coating before it cured
Rain blowing in through an open door, condensation forming on the film overnight, or a slab that was still damp when the coating went down. Water on uncured epoxy leaves a permanent milky haze in the top of the film. Unlike blush this one does not wash off, because it is in the resin rather than on it.
4. Efflorescence
Water moving through concrete dissolves salts and deposits them as a white crystalline powder when it evaporates. If it is on top of the coating it brushes off and looks like chalk. If it is under the coating it is the same story as cause one: moisture is moving and it is bringing the slab with it.
5. Chalking from UV
Prolonged sun exposure degrades the resin at the very surface and leaves a dull white powder. It rubs off on a hand. This goes with fading and gloss loss rather than with dampness, and it is often accompanied by yellowing in the same areas.
6. Cleaning damage
Strong alkaline cleaners, repeated use of an unrinsed soap, or hard water deposits can leave a dull white cast. Least serious on this list, and usually fixed by changing what is used on the floor.
Narrowing it down
How to tell which one you have
| What you see | Most likely cause | Check this |
|---|---|---|
| White under the film, coating lifts around the patch | Slab moisture | Calcium chloride or relative humidity probe test. |
| Hazy greasy film, hard glossy coating underneath | Amine blush | Humidity and dew point on the day you coated. |
| Milky haze in the film, will not wash or abrade out | Water on uncured epoxy | Was there rain, condensation or a damp slab during cure? |
| White crystalline powder, gritty, brushes off | Efflorescence | Where the water is coming from and whether it is under the film too. |
| Dull powder that rubs off, floor also faded | UV chalking | Sun exposure and whether the top layer was light stable. |
| Patchy dull cast following a mop pattern | Cleaning chemicals or hard water | What the floor is being washed with, and whether it is rinsed. |
| Worst near drains, exterior walls and low spots | Localized moisture | Test those areas specifically rather than the middle of the room. |
The repair
Can it be fixed in place?
Blush, efflorescence on top, cleaning haze
Yes, and easily. Wash with clean water and a scrub pad or an auto scrubber, rinse, let it dry completely, abrade, then recoat. Change the cleaning routine so it does not come back.
UV chalking
Abrade off the degraded surface layer and recoat with something light stable. A polyaspartic or aliphatic polyurethane top layer stops it recurring, which a clear epoxy will not.
Haze inside the film from water during cure
The discoloration is in the resin, so it cannot be washed out. If the coating is otherwise sound, grinding back the affected top layer and rebuilding is usually enough. If the water sat on it long enough to affect the cure, the area comes off.
Moisture from the slab
Here is the honest answer. Nothing you apply on top of the floor changes what the slab is doing. A topcoat over a floor that is whitening from below traps the moisture and the failure continues underneath where you cannot see it, until it blisters and peels.
The real fix is to remove the coating, test the slab properly, and rebuild with a moisture vapor barrier sized to the vapor drive you actually measured. That is a grind and a full rebuild, and we would rather tell you that now than sell you a pail of topcoat that buys six months.
If the slab is an exterior deck, a balcony or anything over occupied space, stop before you buy a barrier. That is a waterproofing job rather than a coating job, and it takes a waterproofing system with a proper membrane. A moisture vapor barrier is designed to hold back vapor from below, not to keep standing water out from above.
Next time
The prep that prevents it
Test the slab, always
Not a guess, not a plastic sheet taped down overnight as the only check. Run the proper tests, in the wet areas as well as the middle of the room, and keep the numbers. They tell you whether you need a barrier and which one.
Use a barrier when the numbers say so
A moisture vapor barrier is a specific product doing a specific job. A primer is not a substitute for one, and neither is an extra coat of epoxy.
Watch the dew point before you coat
If the slab is near or below the dew point, condensation will form on the film. Check the forecast and the slab temperature, not just the air temperature.
Close the building
Doors shut, no blowing rain, no washdown upstream, no condensation dripping off equipment. An open roll-up door during an evening pour has ruined a lot of floors.
Finish with a light stable wear coat
It stops UV chalking, it takes the cleaning chemicals instead of the build coat, and it can be refreshed later with an abrade and a recoat.
Related symptoms
Often confused with
Talk to somebody who has stood on a slab
Tell us what you are seeing
This page is general guidance. Whitening has several possible causes and a web page cannot see your concrete. Tell us whether the white washes off, whether it disappears when the floor is wet, and what the underside of a lifted piece looks like, and we can usually tell you quickly whether this is a wash and recoat or a slab problem.
Latux Epoxy
2201 N Andrews Ave, Suite 108
Pompano Beach, FL 33069
(800) 413-1427
Monday to Friday, 8:00 AM to 5:00 PM.
Saturday by appointment.
Sunday closed.