What the blades are actually doing
Rotating steel blades pass over the same concrete again and again, each pass angled a little steeper than the last, pressing the cream at the surface tighter and tighter until it turns hard and dense. A hand steel trowel does the identical thing, worked by an arm instead of a motor, and on a small area the two finishes look about the same once they cure. What the machine buys is speed and consistency across a floor too big for a hand crew to finish before the concrete sets up past working, and an even burnish from one edge of the slab to the other instead of one corner getting more passes than another.
Why that finish stays indoors
A power troweled surface is smooth on purpose, and smooth concrete is slick the moment it gets wet. That trade makes sense on a warehouse or shop floor under a roof, where the only traffic is tires and boots on dry concrete. It does not make sense on a driveway, a walkway or a patio, where rain, dew and snowmelt are part of the deal. On outdoor flatwork we finish to grip instead, usually a broom drag, because a slab that is slick once and dry does not stay that way through a Virginia winter.
Where we run ours
We own a power trowel the same way we own the forms and the screeds, because enough jobs called for it that borrowing one stopped making sense. It comes out on garage and shop floors, where the concrete lives indoors and a hard, dense surface is exactly what the space needs, not something to work around. On a driveway, a patio or any flatwork that will see weather, that machine stays in the trailer, and we send the crew out with brooms instead. Which floors get power troweled and which get a broom finish usually sorts itself out once you say whether the slab lives under a roof or under the sky.