When people picture polished concrete, they’re usually thinking of a perfectly smooth, glass-like floor with crisp reflections. But here’s the reality most contractors won’t or can’t explain upfront: Not every concrete slab is built to polish like that. And the reason comes down to two things: FF and FL ratings.
What Do FF and FL Actually Mean?
Before we get too deep, let’s simplify it:
- FF = Floor Flatness (how smooth the surface is)
- FL = Floor Levelness (how level the slab is across a distance)
Both are measured when the concrete is poured—but they have very different impacts on the final polished result.
FF (Floor Flatness): The One That Really Matters for Polishing
FF measures how much the surface rises and falls over short distances—basically the “waves” in the floor.
Why this matters:
- Low FF = visible ripples and distortion in reflections
- High FF = sharp, clean, mirror-like finish
- Low FF = more grinding, more labor, more cost, inconsistent aggregate exposure
Think of it like this:
If the slab isn’t flat to begin with, polishing just makes the imperfections more noticeable. As a slab is polished, the light reflectance increases. This will amplify the visibility of the “waves” in a low FF floor. Also keep in mind, the more the floor is ground to flatten, the more the aggregate is exposed. As the high spots are ground down, the bigger the exposure becomes. This creates uneven stone/aggregate size. See our article “Polished Concrete- Aggregate Levels and Expectations” discussing aggregate levels on polished concrete.
We can improve flatness during grinding—but we cannot completely change the structure of the slab without major cost.
FL (Floor Levelness): Important, But Less Visual
FL measures how level the floor is over longer distances.
Why it matters:
- Affects drainage and water movement
- Important for warehouses, forklifts, and equipment
- Not usually what causes a “wavy” polished look
You could have a floor that’s perfectly level (good FL)…
…but still looks terrible when polished if the FF is low.
Typical FF / FL Ratings (And What They Mean for You)
| Floor Type | FF | FL |
| Basic residential slab | 20–25 | 15–20 |
| Standard commercial | 35–45 | 25–35 |
| Polished concrete ready | 50–70+ | 40–60+ |
The Problem We See All the Time
A customer wants:
“That high-gloss, showroom-style polished concrete.”
But the slab they have is:
- Standard pour
- Not laser screeded
- Average FF rating
The result?
- Visible waves
- Distorted reflections
- Extra grinding time to improve it (but not perfect it)
What You Should Know Before Polishing
If you’re planning a polished concrete floor, ask about FF rating before the pour. If it hasn’t been poured yet, this is your biggest opportunity. The cost will run higher for the higher FF rating due to the extra labor involved to achieve, but the result will be a more uniform polish. If your slab is already poured and finished, you’ll want to do research so that you understand what your slab can realistically achieve. We’ll always maximize what’s there—but the expectations need to match the slab. Know where your money goes
Lower FF floors require:
- More grinding passes
- More tooling wear
- More labor
Can You Fix a Low FF Floor?
Yes… to a point.
We can flatten high spots, blend inconsistencies, and improve overall appearance. But we can’t turn a standard slab into a true super-flat floor. With heavy grinding, we can flatten a low FF floor, but that will generate inconsistencies in aggregate exposure. Self-leveling overlays are an option, that said this route can drastically increase expense and add days to the project schedule. There is also the less popular solution, that being a remove and repour of the slab. This is usually not a practical route to take.
Final Takeaway
If you remember one thing, it’s this:
FF controls how your polished concrete looks.
Not the sealer.
Not the grit level.
Not the shine.
It all starts with the slab.