When is it appropriate to use a bull float?

Using a bull float is most appropriate when the floor flatness (FF) number is below 20. This is because a bull float is designed to help level and smooth the surface of fresh concrete, particularly over larger areas, before finishing. When the FF number is below 20, it often indicates that the surface is rough or uneven, so using a bull float can effectively reduce imperfections and enhance the overall flatness of the surface.

The bull float helps to fill in low spots and bring the paste to the surface, which is crucial in achieving the desired finish for flatwork applications. It's also advantageous in early-stage finishing processes when the concrete is still workable. While it is important to consider the condition of the surface, using a bull float specifically corresponds to how flat or even the surface is based on the FF number to ensure quality in the finishing process.