What is power floating?
Power floating is finishing a fresh concrete slab or sand and cement screed with a power float, a machine whose motor drives a rotating pan or steel blades across the surface. It flattens high spots, fills small hollows and compacts the top of the floor, leaving a dense, even finish.
You will also hear it called power trowelling, although strictly the two are different passes. Floating, with a flat pan or blades held flat, comes first and leaves a slightly textured surface. Trowelling, with the blades tilted, comes later and closes the surface to a smooth, very dense finish.
How a power float works
The Designing Buildings Wiki describes a power float as a hand operated machine with a motor or petrol engine mounted over a circular pan, with steel blades that rotate at up to 150rpm. The operator usually works from one end of the area to the other, walking backwards, at a slow and consistent speed. After the floating passes, the blades are angled to suit the concrete and the finish asked for; blade angles of around 5 to 10 degrees are usual, and may be increased after each pass.
When to start
Timing is the whole skill. The Concrete Society notes that power floating is carried out later than hand floating, because the concrete has to take the weight of the machine. Its rule of thumb is that the heel of a boot should leave only a slight impression, around 3mm. The Designing Buildings Wiki gives a similar guide of indentations of 3 to 4mm when you walk on the surface.
Start too early and the machine tears the surface or works bleed water back into it, which weakens the top layer. Start too late and the high and low spots can no longer be corrected. How long that window takes to arrive depends on the mix, the air temperature and the humidity, which is why there is no fixed number of hours.
Power floating on concrete and on screed
On a ground bearing concrete slab, power floating can produce a surface good enough to take a floor finish directly, and the Designing Buildings Wiki notes that it removes the time and materials of a separate finishing screed. Whether that works depends on how flat and level the slab needs to be for the floor going on top.
On a sand and cement screed, the power float closes and densifies the surface after the screed has been compacted and ruled off to level. On larger areas we power float our sand and cement screed to give a consistently tight surface, and the same finish is used on our fibre reinforced screed, where it closes the surface over the fibres.
Liquid screeds are not power floated. They level themselves and are finished by dappling, pushing a bar or brush through the wet screed in two directions to release trapped air.
The finish it gives
- Power floated. A flat surface with a slight texture, often with circular swirl marks from the machine.
- Power trowelled. A smooth, very dense surface, from later passes with the blades tilted.
- Burnished. Too many passes can give a polished, burnished look, which may not be the finish that was specified.
For a floor that will be tiled, glued or levelled, the surface still has to be clean and sound. Over working a surface is one of the causes of laitance, the weak, dusty top layer that has to come off before bonding anything to it.
Common mistakes
- Starting before the bleed water has gone. The Concrete Society warns that trowelling before bleed water has evaporated risks delamination of the surface.
- Power trowelling air entrained concrete. Not recommended, again because of the risk of surface delamination.
- Too many passes. The Concrete Society notes that over working gives a burnished appearance, and power floating can sometimes lead to surface delamination.
- Using the float to fix levels. A power float refines a surface that has already been ruled off to level; it does not correct a badly laid floor.
- Skipping curing. The MPA advises covering screeds with plastic sheeting or similar to retain moisture for at least five days after laying.
How this relates to our services
We do not hire out power floats or sell machines. We use them on the screeds we lay, most often on larger sand and cement and high strength screed floors, where a tight, hard wearing surface matters. If you want to know whether your floor needs a power floated finish, tell us what is going on top.
Sources
- Floated and trowelled finishes, The Concrete Society, June 2025, accessed 25 October 2026
- Power float, Designing Buildings Wiki, accessed 25 October 2026
- Laitance, Designing Buildings Wiki, accessed 25 October 2026
- Mortar data sheet 22: Screeds, Mineral Products Association, issue 3, October 2023
- Installation of Cemfloor screed, Cemfloor, accessed 25 October 2026
Part of our screeding glossary, which defines every term we use on site.
