In commercial construction, "flat" isn't an opinion; it's a mathematically measured standard. We deal constantly with F-Numbers: Floor Flatness (FF) and Floor Levelness (FL). If you are pouring a warehouse that will utilize high-reach, narrow-aisle forklifts, a bump or dip of just a few millimeters can cause the forklift to sway dangerously 10 meters in the air. Passing these stringent laser inspections starts the moment the vibratory screed hits the wet concrete.
Hand screeding inevitably leaves a slightly undulating surface because humans naturally pull with varying pressure. A rigid, mechanically vibrated screed board changes this dynamic. Because the magnesium or aluminum blade is extruded to exact tolerances, it acts as a perfect straightedge. As I walk backward with the machine, the vibration ensures that the concrete fills every micro-depression behind the blade.
However, achieving high F-numbers with a power screed requires mastery of the "wet screeding" technique. Unlike riding the machine on pre-set wooden or steel forms, wet screeding involves shooting laser elevations to create perfectly level "pads" of wet concrete, and then resting the edges of the screed blade on those wet pads to strike off the area between them. It requires a machine with a perfectly tuned throttle; if the engine bogs down under the weight of the mud, the blade will dig in and ruin your FF rating. For high-spec commercial floors, the vibratory screed is the critical bridge between a rough pour and a laser-perfect finish.
