Flooring
The Subfloor Decides the Floor
Moisture, Levelness and the Tests That Come Before Product Selection
Fitness flooring fails in a small number of predictable ways, and the most expensive of them is decided before anyone opens a sample box. It is not a flooring problem. It is a concrete problem that arrives wearing the floor’s name.
Concrete releases moisture for a long time, and adhesive is what notices
A slab that looks dry is not necessarily dry. Water continues to move up through concrete long after the surface is walkable, and when an adhered floor is installed over a slab still releasing it, the moisture has nowhere to go — the result is adhesive failure, bubbling, and a floor that has to come up. On a fitness project that means the room closes twice.
This is why the tests exist, why they are the flooring manufacturer’s condition rather than an optional check, and why they are scheduled rather than squeezed in: the useful ones take days, not minutes.
The two tests, and what each one actually measures
They answer different questions, and a flooring manufacturer will specify which one it wants and at what limit. That limit is a condition of the warranty.
ASTM F2170 — relative humidity, measured inside the slab
In-situ probes are placed in holes drilled into the concrete and left to equilibrate before being read, so the measurement describes the moisture condition within the slab rather than at its surface. It is the test most manufacturers now specify, because a surface can be dry while the body of the slab is not.
ASTM F1869 — moisture vapor emission rate, measured at the surface
The calcium chloride test measures how much moisture is emitting from the surface over a set period. It is the older method and still specified, and it answers a surface question rather than an internal one — which is precisely why the two are not interchangeable and why the manufacturer’s stated method is the one to run.
Levelness is the second property, and rubber hides nothing
A resilient floor conforms to what is under it. Dips, ridges, trowel marks and the line where two pours met all telegraph through, and on a large open fitness floor under directional lighting they are visible from the door. Grinding or a self-leveling underlayment is ordinary preparation, not a defect being covered up — but it is work, it has a cost, and it belongs on the schedule rather than in a discovery on install day.
It matters mechanically as well. Equipment on an uneven floor sits on three of its four feet, which is how a rack rocks under load and a treadmill develops a noise nobody can locate.
Height differences at the edges are where a floor lifts first
Where a new build-up is thicker than what it meets — at a doorway, at a mirrored wall, at the transition from rubber to turf or to a studio floor — the height difference is both a trip hazard and the first place the material starts to lift. Specify the transition at the same time as the surfaces, and decide who owns the difference between two products of different thickness before anyone is standing in the room with a trim piece. Which thickness goes where is a separate decision, made by activity: a cardio bank and a drop zone are different answers.
The order that avoids all of this
- Test first, select second. The manufacturer’s method and limit decide what is available to you, so testing before selection saves choosing a product the slab will not accept.
- Schedule the test. Equilibration takes days. A test squeezed into the week of install is a test that produces a number nobody can act on.
- Price the preparation. Grinding and leveling are ordinary and should be a line, not a surprise.
- Specify transitions with the surfaces. Not on site, and not by the installer holding whatever trim was on the truck.
What the finished floor should be doing for each part of the room is on our commercial fitness flooring page.
Published August 17, 2026 · 5 minutes read
In short
Two properties of the slab decide what can go on it, and both are measured rather than judged by eye. Moisture is tested with in-situ relative humidity probes under ASTM F2170 or calcium chloride under ASTM F1869, and the manufacturer of the flooring sets the limit its warranty depends on. Levelness is the second: rubber telegraphs whatever is beneath it, so an uneven slab shows through the finished floor. Both are answered before product selection, in the same conversation as the 100 psf live load a fitness floor is designed for.
Part of what we do on commercial fitness flooring.
Common questions
Why does concrete need to be tested before gym flooring is installed?
Because moisture still moving up through the slab has nowhere to go once an adhered floor is over it, and the result is adhesive failure and a floor that has to be lifted. The flooring manufacturer sets a moisture limit as a condition of its warranty, so the test is a requirement rather than a precaution.
What is the difference between ASTM F2170 and ASTM F1869?
F2170 measures relative humidity inside the slab using in-situ probes left to equilibrate before reading; F1869 measures moisture vapor emission at the surface using anhydrous calcium chloride. They answer different questions and are not interchangeable — run the method the flooring manufacturer specifies, at the limit it states.
How long does concrete moisture testing take?
Days rather than minutes, because in-situ probes have to equilibrate before they can be read and the calcium chloride method runs over a set period. That is why it is scheduled ahead of product selection rather than squeezed into the week of installation, when the result arrives too late to act on.
Does an uneven slab matter under rubber flooring?
Yes. Resilient flooring conforms to what is under it, so dips, ridges and trowel marks telegraph through and are visible across an open floor under directional lighting. It is also mechanical: equipment on an uneven floor sits on three of four feet, which is how a rack rocks under load.
Who is responsible for floor preparation on a gym project?
It should be assigned explicitly in the scope before work starts. Grinding and self-leveling underlayment are ordinary preparation with a real cost, and the transitions where a thicker build-up meets a doorway or another surface should be specified alongside the surfaces rather than resolved on site.