When your epoxy floor fails and the installer blames moisture in the slab, the claim can be true. It can also be the easy way to hand you the bill for a bad install. The slab leaves clues either way. Read the damage, ask for the ASTM F1869 or ASTM F2170 test data, and take the 5 steps near the end of this guide before you pay for a redo.
Floor coating is a hard trade. Every crew makes mistakes, and we’ve made ours. What counts is what happens next. This guide isn’t about any one company. It’s about the day a floor comes apart and someone says “it’s your slab,” and how you can tell if the numbers back that up. For every way a coating can fail, start with our epoxy floor failure guide. This page picks up where the argument starts.
Is the slab really to blame, or is it the easy answer?
Sometimes it really is the slab. Water vapor, which is moisture in the form of a gas, moves up through concrete all the time. A coating stops it at the top. When a calcium chloride test reads above about 3 pounds, most coating systems need a moisture barrier primer first. A floor that went down without one can lift. That’s a real failure, and a fair warranty on your floor can leave it out.
The trouble is that moisture is the one cause you can’t see. Blame the prep, and you point at the crew. Blame the resin, and you point at the company that made it. Blame moisture, and you point at the concrete, which belongs to you or your builder.
If your floor is in Seminole, Shawnee, Tecumseh, Konawa, Wewoka, Beggs, or anywhere in Seminole and Pottawatomie counties, moisture is a fair question. Many homes and shops there sit on a slab poured right on the ground. It still needs a fair answer, and that means a test and a number.
What does moisture damage look like under a coating?
Moisture damage under a coating has a look, and it’s hard to miss. Water vapor rising through a slab carries salts along with it. When the coating stops the vapor, the water and salts pile up right where the coating meets the concrete. You get blisters that hold liquid when you pop them. You get a white or milky haze under a clear coat. You see efflorescence, a crust of white salt, at the edges and along the walls. And the coating lets go of the slab, so it sounds hollow when you tap it with a coin or a screwdriver handle. This damage spreads across wide areas. It gathers in the lowest spots, where the least air moves. Small, separate patches of fine cracks, with coating still stuck tight all around them, match none of those signs. That pattern points at how the coating went down, not at the concrete.
| What you see | What it usually points to |
|---|---|
| Liquid-filled blisters, white haze, salt at the walls, hollow sound across wide areas | Moisture from the slab; ask for ASTM F1869 or ASTM F2170 data |
| Small checked or cracked patches, with bonded coating all around them | Heat or mixing trouble during the install |
| Sheets peeling off with smooth, bare concrete on the back | Poor grinding or a skipped primer |
| Lifting only under tires, in hot weather | Hot-tire pickup, a coating and cure problem |
If there’s a bare spot near the damage, try the 18-inch plastic square test from our moisture testing guide before anyone argues about lab numbers. It takes about 16 hours. It tells you whether the slab even belongs in the argument.
What damage points at the crew instead of the slab?
Epoxy gets hot as it cures. A big mass of mixed epoxy, like a full bucket left sitting or a loaded roller set down on the floor, can build heat faster than it can let it go. The trade calls that an exotherm. Epoxy that cures too hot and too fast turns brittle. Then it checks into fine surface lines and cracks.
That leaves a clue you can measure with a tape. We’ve seen the only cracked spot in a room turn out to be a rectangle about 9 inches long. That’s the size of a roller cover. It sat right where a crew would set the roller down while mixing the next batch. Moisture from below doesn’t draw a box the shape of a roller. It shows up wherever the slab is wet. So if your damage sits in neat shapes near a doorway, a corner, or the spot where the mixing station stood, ask about the install before you ask about the concrete.
What does an honest moisture test look like?
Two tests count, and each one has rules. ASTM F1869 is the calcium chloride test. The tester cleans a bare spot and weighs a dish of dry salt. The dish goes under a plastic dome sealed to the bare concrete. After about 60 to 72 hours, the tester weighs it again. The weight it gained is the moisture that came out of the slab. The result reads in pounds per 1,000 square feet per 24 hours. Before the test starts, the building should sit at normal living conditions for about 48 hours.
The standard also sets a count. It calls for three tests in the first 1,000 square feet, plus one more for each 1,000 after that.
| Floor size | Calcium chloride tests the standard calls for |
|---|---|
| Up to 1,000 sq ft | 3 |
| 2,000 sq ft | 4 |
| 3,000 sq ft | 5 |
| 5,000 sq ft | 7 |
Two kits on a 2,000 square foot floor is half the count.
The dome seal matters most. If the dome doesn’t seal tight to bare concrete, the salt pulls water out of the room air too, and the number climbs. In a humid house, a kit that isn’t sealed can make a dry slab read like a wet one. Ask for a photo of each kit in place, with the seal in view.
ASTM F2170 is the other test. It measures relative humidity, or how damp the air is, inside the slab. A probe sits in a drilled hole for at least 24 hours, and usually longer. That way it reads the air inside the concrete, not the room air or the air stirred up by the drilling. A reading taken minutes after drilling doesn’t count, no matter how high it reads.
Can a slab test at 10 pounds one week and under 3.5 the next?
We’ve retested slabs where the installer’s kits read 8 and 10 pounds, and ours, a few days later, all read under 3.5. A slab doesn’t dry that fast. One of those tests was not run right. Water leaves concrete over weeks and months, not over a long weekend. A true reading of 10 pounds can’t fall below 3.5 in a few days. So when two calcium chloride tests on one slab are that far apart, look at how each set went down. Were the domes sealed to bare concrete? Did someone weigh each dish on a scale before and after? Did the kits sit about 60 to 72 hours? Were there enough of them for the square footage? Trust the set that can answer yes to all four, with photos and dates. The fairest retest has both sides in the room, watching the same dishes go down and come back up.
What if the installer blames the metallic pigment instead?
Metallic floors get their own version of this fight. When a metallic epoxy floor comes out streaked or full of craters, the blame sometimes lands on the pigment. Metallic pigment is fine bits of metal or mica, and nothing in it spoils. We still use metallic pigment we bought in 2000, about 25 years on the shelf.
The usual causes are in how the floor went down:
- A short pre-blend. Fine metallic pigment needs about 10 minutes of mixing in the Part A resin, with the bottom of the bucket scraped, before the hardener goes in. A 2-minute mix leaves clumps, and they flow out as dark streaks.
- A primer that left pinholes or got too hot. A primer coat usually leaves about a 36-hour window when the next coat bonds well. If the primer overheats and cures hard, that window closes early. Then the metallic coat pulls away in craters.
- Grit from dirty spike shoes. Crews walk on wet metallic coats in spiked shoes. Dirt on the spikes drags through the coat and leaves specks and trails.
- No test patch. A sample of about 10 square feet in a corner or closet shows the color, the flow, and any flaws before the crew does the whole floor.
What does “hydrostatic pressure” mean in the warranty on your floor?
When the blame turns to moisture, read the exact words in the warranty on your floor. Many of them don’t cover “hydrostatic pressure.” That means groundwater pushing up on the bottom of the slab, and it takes soaked soil or a high water table. The two tests above can’t see it. ASTM F1869 reads the vapor leaving the top of the slab, and ASTM F2170 reads the humidity inside it. No field test measures the pressure under a floor that’s already coated.
Once a floor fails, an installer can name hydrostatic pressure, and nobody can prove it true or false. Our guide to the warranty on an epoxy floor walks through that clause and 9 others we found in real warranties across 6 states.
A clause nobody can test for is a way out
If nobody can test for a condition, an installer can name it after any failure, and you have no way to prove them wrong. Before you sign, ask which test and which number would prove that condition, and who pays for the test.
Who pays when nobody tested before the coating went down?
Knowing the slab before the coating goes down is the installer’s job. The installer picks the system, the primer, and the thickness, and each of those choices depends on how much moisture the slab gives off. A good crew checks the slab first and runs a test when the check shows a warning sign. A calcium chloride kit or a humidity probe costs very little next to a failed floor. If a test reads above about 3 pounds, the answer is a moisture barrier primer. It goes down before the coating, not after, and ours adds $1.80 a square foot. When an installer skipped the test, coated the slab, and now blames moisture, the blame is weak. They had the chance to measure the slab and passed on it. If they did test, ask to see the result they had the day they coated. A slab that tested wet and got coated anyway points back at the same crew.
That’s how we read it as a contractor. It isn’t legal advice. A fight over real money is worth an hour with a lawyer who handles construction contracts.
Five steps before you pay for a redo
- Ask for the test data in writing. Get the method (ASTM F1869 or ASTM F2170) and the number of tests for your square footage. Get the dates each test started and ended, and a photo of each kit or probe in place.
- Look at the damage pattern. Wide blisters, haze, salt, and hollow spots point at the slab. Small boxes and patches with bonded coating all around them point at the install. Take dated photos of every spot.
- Get a retest from someone with no stake in the answer. They set new kits to the standard, and both sides watch the dishes get weighed, placed, and read.
- Get the finding in writing. A written report with the numbers gives both sides something to settle on besides opinion.
- Hold off on paying for a redo until you have that report. A new floor over a wet slab spends the money twice. So does paying for a redo that covers the installer’s own mistake. Plan on about a week for a fair retest.
Before you hire anyone again, read our workmanship warranty for floors. Then ask every installer, us included, the same questions about testing.
Getting ego out of the way
Every floor contractor gets a callback sooner or later, and we’ve had ours. The honest answer comes from the test data, not from who pays for the fix. We put it this way: “The contractor really needs to get ego out of the way and learn to value the truth, even when it falls in a way that’s not in your favor.”
A test up front costs a few days, usually about 3, and it saves both sides a fight later. Our epoxy flooring service checks slab moisture before we pick a product, and we test when the check turns up a warning sign. If you live anywhere in Seminole and Pottawatomie counties, our epoxy flooring page for Seminole customers covers the floors we coat in your area. When you want real numbers for your own floor, get your price now.
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