Bull floats are used after screeding when the specified F-number floor flatness is ____ or less.

• A. 20
• B. 15
• C. 25
• D. 30

Answer: (A)

F-number measures how flat the concrete floor is—the smaller the number, the flatter the surface. After screeding, you use a bull float when the floor has reached a low F-number (roughly twenty or below) because at this level the surface is flat enough to accept the float without chasing high spots or causing tears. The bull float helps bring bleeding paste to the surface, closes small voids, and creates a uniform cream that sets up well for final troweling. If the spec allows a higher F-number (the surface is rougher), bull floating after screed can be less effective and may lead to pulling material or creating irregularities, so finishing is timed differently. In short, bull floats are used after screeding on surfaces with a low F-number to produce a smooth, uniform surface ready for final finishing.