A slab can look perfect from the doorway and still miss its flatness spec. On warehouse and retail work across the Grand Strand, that usually shows up after racking goes in, when forklifts start rocking or flooring installers ask for more grinding and patching than anyone budgeted.
Most general contractors and concrete subs already know what FF and FL are. The harder questions are practical ones: when the test has to happen, which numbers actually decide pass or fail, who pays for a retest, and what happens next when a section comes up short. This post covers those.
The short version of the numbers
FF/FL values are calculated under ASTM E1155, the test method most slab specs reference. FF describes flatness over short distances, meaning local waves and ridges. FL describes levelness over longer distances, meaning how well the slab follows its intended elevation or slope. For the full method and deliverables, see our floor flatness and levelness testing service.
Specified overall values versus minimum local values
Most specs set two kinds of numbers for each of FF and FL:
- •**Specified overall values** apply to the floor as a whole, combined across all test sections.
- •**Minimum local values** apply to each individual test section, and are lower than the overall values.
This is the part that catches teams off guard. A floor can meet its overall values and still have one section below the minimum local value, and that section can still require correction. Read the spec for both sets of numbers before the pour, and make sure the finishing crew knows them too.
When the test has to happen
ACI 117, the tolerance standard most specs reference, calls for FF/FL measurements within 72 hours after the slab is finished. On elevated slabs, the measurement also has to happen before shoring is removed, because deflection after the shores come out changes levelness and is not a finishing issue.
In practice, the test gets scheduled before the pour, not after someone notices a problem. Plan for access the day after finishing when you can, before pallets, lifts, or other trades cover the floor. A missed window can leave the team arguing over data nobody can rely on.
Who calls for the test
Owners and designers usually set FF/FL requirements in the concrete or flooring spec, often because of racking, forklift traffic, or a floor finish that will telegraph every bump. The general contractor typically schedules the test as part of quality control, and sometimes the owner hires an independent tester. Either way, settle who orders it and who receives the report before the pour, so results go to the right people the first time.
What happens when a slab misses spec
A failed section does not automatically mean tearing out concrete. The usual paths, depending on the spec and the use of the floor, are:
- •**Grinding** high areas back into tolerance
- •**Filling or topping** low areas with an approved material
- •**Accepting** the section, sometimes with a credit, when the owner and designer agree the floor still works for its use
The decision belongs to the owner, the designer, and the engineer of record, not the tester. What the tester can do is show exactly where the problem is.
Who owns the retest
Retests are where cost disputes start. Common arrangements put the retest cost on whoever caused the miss, which usually means the concrete sub after a finishing problem. But the contract decides, not habit. Before the pour, confirm in writing who pays for a retest, whether remediated areas get retested alone or the whole floor gets retested, and whether the same method has to be used for the retest.
Why a heat map helps the conversation
Traditional line methods produce numbers for each test line. A laser scan captures the whole slab and can produce FF/FL values along the required lines plus a deviation heat map of the entire floor. When a section fails, the heat map shows the GC, the sub, and the owner the same picture of where the high and low zones are, so grinding or filling can be targeted to marked areas instead of guessed. Confirm with the designer that the method satisfies the spec before relying on it.
How fast the report comes back
Turnaround matters because the remediation decision often has to happen before the next trade moves in. Agree on a report due date when you schedule the test, and ask for a pass or fail summary first if the full report will take longer. The same scan data can later support racking layout or as built documentation, which we cover in As Built Laser Scanning Before You Bid.
What to send before the pour
- The specified overall and minimum local FF and FL values
- The pour date and finishing schedule
- Whether the slab is on grade or elevated, and when shoring comes out
- Who orders the test, who receives the report, and who pays for a retest
- Areas with special requirements, such as racking aisles or equipment pads
Get started
If you are pouring warehouse, retail, or light industrial slabs on the Grand Strand, Estate360 can schedule FF/FL testing inside the spec window and deliver a report your team can act on. Reach out at sales@estate360.us, through estate360.us/contact, or by phone at 843-306-8063.