ACI Floor Flatness & Levelness (FF/FL Numbers) 2

Question 1

What is the fundamental difference between floor flatness (FF) and floor levelness (FL)?

Accepted Answer

FF measures short-interval surface waviness; FL measures long-interval slope relative to a horizontal plane

Answer

FF measures local curvature over short distances (bumps and dips), while FL measures the long-range slope or tilt of the floor relative to a horizontal plane.

Question 2

When should F-number measurements typically be taken after concrete placement per ASTM E1155?

Accepted Answer

Within 72 hours of slab placement

Answer

ASTM E1155 recommends F-number measurements within 72 hours of placement to capture the as-built profile before curling and drying shrinkage alter the surface.

Question 3

A typical minimum FF number for a conventional warehouse floor with random forklift traffic is approximately:

Accepted Answer

FF 20–35

Answer

ACI 117 and industry standards typically specify FF 20–35 for conventional warehouse floors subject to random forklift traffic.

Question 4

How does finishing concrete before bleed water has evaporated affect floor flatness and surface quality?

Accepted Answer

It can trap bleed water beneath the surface, causing dusting, delamination, and compromised FF values

Answer

Finishing over bleed water seals it beneath the surface, weakening the surface layer and potentially causing dusting and delamination, which compromises both surface quality and FF measurements.

Question 5

In the F-number system, what does an F-number of zero indicate?

Accepted Answer

An uncontrolled floor surface with no flatness specification met

Answer

An F-number of zero indicates a random, uncontrolled floor surface with no flatness specification being achieved — representing the worst possible condition.

(ACI) American Concrete Institute Concrete Finisher Practice Test

(ACI) American Concrete Institute Concrete Finisher Practice Test

ACI Floor Flatness & Levelness (FF/FL Numbers) 2