Delaying troweling until the concrete is too stiff to close up reduces the possibility of delamination and makes it easier to achieve high flatness F-numbers. True or False?

• A. True
• B. False
• C. Not sure
• D. It depends

Answer: (B)

Timing of troweling is crucial for both surface bonding and achieving a smooth, flat finish. If you delay finishing until the concrete is too stiff to close up, the surface can become a weak, highly laitance-rich layer that doesn’t bond well to the underlying concrete. That weak bond increases the risk of delamination between the surface and the sublayer. At the same time, a surface finished in that late, stiff state won’t respond well to smoothing, so you’re likely to leave unevenness and ridges that keep the F-numbers from being high. The right approach is to finish while the surface has stiffened enough to hold shape but is still plastic enough to be closed and blended consistently. Delaying too long does not reduce delamination or improve flatness; it tends to worsen both.