Petrographers' reports often cite premature finishing as a major cause for blistering and delamination. And numerous publications tell finishers to avoid floating slabs too soon. But what is premature finishing, and how precise are the methods finishers use to judge the proper time for finishing operations to begin?

The time gap between premature and late finishing can be a small part of the finishability window. Deciding when to start power floating operations may be the most crucial decision the finisher makes. Starting to power float too early can result in surface defects. Waiting too long can lead to unacceptable floor-flatness measurements or a poor surface finish.

For years, finishers have used two general guidelines to decide when to start finishing operations: when no bleedwater is visible on the slab surface, and when a footprint no deeper than 1/8 to 1/4 inch is made in the slab. But these guidelines aren't infallible and don't always prevent floor-surface defects. Finishers also must balance the effects of concrete property variations, the ambient environment (wind, sun, relative humidity and rain), crew size and equipment availability to hit the gap between premature and late finishing.