The finishing quality of concrete can be gauged by different tolerances, which are defined in local building codes.
For example, in the USA following 4 classes of concrete finishing are defined by the American Concrete Institute (ACI). These classes are gauged by measure the vertical distance below the straight edge place on the concrete surface.
- Class A finish- 1/2 inches below a 10-foot straight edge.
- Class A-2 finish- 3/16 inches below a 10-foot straight edge.
- Class B finish- 1/4 inches below a 10-foot straight edge.
- Class C finish- 1/4 inches below a 2-foot straight edge.
Class C finish is the worst quality of finish as it includes the biggest heaps.
Similarly, in Australia, a different tolerance system exists. It is recommended there to check the quality of finish produced by the float by placing a 3m (10 foot) straight edge on the concrete surface.
If any high spots are detected, the concrete should be floated again and again until all the high spots disappear. The tolerance of any machine trowel depends on the shape of its blade fans. Usually, it is specified by the manufacturer.
In any case, as discussed earlier, you can improve the quality of finish by increasing the number of floats passes.