The Other Reason Floors Fail
Why Coatings Fail From Underneath
Bad prep is the failure people can imagine. Moisture is the one that gets missed — because it happens below the floor, and nothing about it is visible until the coating starts letting go.
Your floor is sitting on wet ground
Concrete looks solid. It isn’t sealed. It’s full of microscopic capillaries, and it’s poured directly onto soil — soil that holds water, and holds more of it after rain, snowmelt, or a season of bad grading around the house.
Water in that soil doesn’t sit still. It moves up through the concrete as vapor, constantly, in every direction it can. On an uncoated garage floor you never notice, because the vapor reaches the surface and evaporates into the room.
Put a coating on top and you’ve closed the exit. The vapor keeps coming, reaches the underside of the coating, and has nowhere to go.
What that looks like when it goes wrong
Pressure builds at the bond line — the boundary between the coating and the concrete. It shows up as:
- Blisters and bubbles, often the size of a coin, sometimes a dinner plate, appearing weeks or months after the install.
- Delamination — sheets of coating lifting away cleanly, with concrete dust still stuck to the back of them.
- A white, chalky haze at the edges of lifted areas, which is mineral salt carried up out of the concrete by the moving water.
The distinguishing feature is that the coating itself is usually intact. It hasn’t worn out or broken down. It has been pushed off, in one piece, from below.
Why it gets skipped
Testing costs money and takes time, and the customer can’t see what it bought.
A moisture test means placing kits or drilling probe holes, waiting — often 24 to 72 hours — then coming back to read them. That’s a second trip before a single dollar of coating has been sold, on a job that might not close.
So on a fast quote it disappears. Nobody mentions it, nothing gets measured, and the floor is assumed to be fine. Most of the time it is. The rest of the time, the customer finds out in the spring.
How it’s actually measured
ASTM F1869
The calcium chloride test. A weighed dish of dry salt sits under a sealed dome on the floor for a set period, then gets weighed again. The gain tells you how much moisture is coming out of the concrete.
ASTM F2170
Relative humidity probes set into holes drilled into the floor, measuring conditions inside the concrete rather than at its surface. Generally the better indicator of what a floor will do over time.
Multiple locations
One test is a data point, not an answer. Moisture is rarely uniform — it concentrates near exterior walls, expansion joints, and low spots. Sterling runs a minimum of three per floor.
Coating manufacturers publish a hard limit for their products, and it is a condition of their coverage — not a suggestion. Test above it and the system either changes or the job waits.
The check you can do yourself, for nothing
It won’t give you a number, but it will tell you whether to ask harder questions.
Tape a two-foot square of clear plastic sheeting to the concrete — all four edges sealed down tight with duct tape. Leave it 24 hours, then look.
- Condensation on the underside of the plastic, or concrete that has darkened beneath it, means moisture is moving through the concrete.
- Bone dry, no color change is a good sign, though not proof — a single square doesn’t speak for the whole floor, and conditions change with the seasons.
This is the plastic sheet method, ASTM D4263. It is an indicator, not a measurement. It tells you something is happening. It doesn’t tell you how much.
New concrete is a special case
Fresh concrete is full of water by design — it needs it to cure. That water leaves over weeks, and a floor coated too early traps it underneath.
A minimum of 28 days is the standard before any coating goes down. If a floor is younger than that, it either waits or it gets a moisture mitigation system underneath the coating.
If you’ve just had a garage or shop poured, this is worth knowing before you schedule anyone: keeping vehicles off it until it’s coated is worth doing. Oil that soaks into bare concrete adds prep time, and prep time adds cost.
What happens if your floor reads high
It isn’t a dead end. It’s a different system: a moisture vapor barrier primer goes down first, underneath the coating, to hold the vapor back.
That’s a real added cost, and it changes the price — which is the entire reason the test happens before the quote is agreed rather than after the work starts. Nobody likes a number that moves. The way to keep it from moving is to know what’s under the floor before anyone commits.
How Sterling handles it
We test your floor to ASTM F2170 and F1869, minimum three tests per floor, and the results are recorded and given to you.
It’s a priced line item on the proposal, not a hidden step — so you can see it was done, and you can compare it against a quote that doesn’t mention moisture at all.
Prep and moisture are the two things that decide whether a coating stays down. Here’s the other one.
Questions
My garage floor has a white powdery film. Is that moisture?
Usually yes. That’s efflorescence — mineral salts left behind as water evaporates out of the concrete. It means water is moving through the concrete, and it is worth testing before coating.
My basement floor is always cold and a bit damp. Can it still be coated?
Often, yes — but that’s exactly the floor that needs testing first. Basements sit deeper in the soil profile and see more consistent vapor pressure than a garage does.
Does a vapor barrier underneath solve this?
It helps a great deal, and newer construction usually has one. But it can be punctured during the pour, and it does nothing about water already in the concrete. It is a reason to be hopeful, not a reason to skip the test.
My coating is already blistering. Can it be fixed?
The failed coating has to come off, the floor has to be tested to find out what it’s actually doing, and the new system gets chosen from that result. Re-coating over the same conditions gets the same outcome.