Q.: We're generally sold on flowing concrete but we've had trouble in finishing flatwork. The mixes tend to be sticky. Finishers find that the concrete moves under their weight, it drags on the trowel, and the surface sometimes tears. Has anyone found what to do about such problems?
A.: Yes, others have noticed these problems. It helps to use more coarse aggregate or a coarser grading of the fine aggregate.
Another way is to adjust your timing. The trouble is that the concrete appears to be ready to finish before it has actually reached initial set. This happens because there is less bleed water available; the concrete has become stiff from shortage of water, not from setting. Some manufacturers suggest waiting about 20 minutes after the glossy sheen is gone before starting the finishing operations.