Power Trowels

A power trowel, also called a power float, helicopter or concrete trowelling machine, is a machine that finishes the surface of a concrete slab after it has been placed and levelled. It has one or more rotors fitted with steel blades or round pans that turn close to the surface while the concrete is setting. The rotating blades float the surface to embed coarse aggregate, close pores and flatten small irregularities, and then trowel it to a dense, smooth and hard finish. Power trowels are used on almost every concrete floor, from small garage slabs to warehouses covering tens of thousands of square metres.

The machine replaces the hand floats and trowels that finishers once used over the whole surface. On large floors, ride-on power trowels with two or three rotors allow a single operator to finish very large areas in the limited time window between the concrete stiffening enough to support the machine and becoming too hard to work.

Brief History of Power Trowels

For most of the history of concrete floors, finishing was done entirely by hand, with wooden floats and steel trowels used by finishers kneeling on boards. Engine-driven trowelling machines with a single rotor and a guard ring, guided by an operator walking behind, appeared in the mid-twentieth century, and they quickly spread because they reduced labour and gave a more uniform surface.

Ride-on trowels with two counter-rotating rotors followed, allowing one operator seated on the machine to finish much larger areas. Steering was achieved by tilting the rotors, first mechanically and later with hydraulic controls. From the late 1980s, the use of steel pans fitted under the blades of ride-on trowels improved floor flatness on large industrial floors. Since then, ride-on trowels have become larger and more powerful, with hydrostatic drives, joystick steering, electronic blade pitch control and, more recently, remote-controlled and battery-powered versions. Laser screeds and ride-on trowels together transformed the construction of large, flat industrial floors.

How a Power Trowel Works

Rotors. Each rotor carries four or more blades on arms around a central shaft. On walk-behind machines one rotor is surrounded by a guard ring. On ride-on machines two or three rotors turn in opposite directions to balance the torque.
Blades and pans. Floating blades or round steel pans are used in the early stages to open and flatten the surface. Finishing blades are used later to close and polish it. Combination blades serve both purposes.
Pitch. The angle of the blades is adjustable. A flat pitch spreads the weight and floats the surface, while a steeper pitch increases pressure for final trowelling. Pitch is set by a handle, a crank or electric controls.
Drive. A petrol, diesel or electric motor drives the rotors through a gearbox, or through hydraulic motors on hydrostatic machines.
Steering. A walk-behind trowel is steered by the operator pushing and lifting the handle. A ride-on trowel is steered by tilting the rotors with levers or joysticks, so that the machine moves in the direction required.
Speed. Rotor speed is increased as the concrete hardens, with high speeds used for burnishing the final surface.

Types of Power Trowels

Walk-Behind Power Trowels

Single-rotor machines with rotor diameters typically from about 60 cm to about 1.2 m. They are used on small slabs, edges, corners and areas near walls and columns that larger machines cannot reach.

Ride-On Power Trowels

Machines with two, or sometimes three, rotors and a seat for the operator. They cover large areas quickly and apply more weight to the surface. Rotors can be overlapping or non-overlapping, which affects coverage and the finish near edges.

Edging Trowels

Small machines designed for working close to walls, columns and penetrations where standard trowels cannot reach.

Remote-Controlled and Electric Trowels

Newer machines operated by remote control or powered by batteries, used indoors to cut emissions and in some cases to reduce operator exposure.

Size Classes

Class	Typical size	Typical use
Walk-behind	rotor about 60 to 120 cm	Small slabs, edges, residential and repair work
Small ride-on	overall about 1.5 to 2.5 m	Medium slabs and elevated decks
Large ride-on	overall about 2.5 to 3.7 m	Warehouses, industrial and commercial floors

Figures are indicative. Ride-on trowels range from a few hundred kilograms to more than 900 kg, and heavier machines apply more pressure for finishing.

Accessories

Power trowels use several interchangeable finishing tools. Float blades are wide and turned up at the edges to ride on softer concrete. Finish blades are narrower and used when the surface is harder. Combination blades offer a compromise for smaller jobs. Float pans, which clip onto the blade arms, spread the machine weight over a large area and flatten the surface in the early stages. Other accessories include lifting and transport devices, retarder and water spray systems, lighting for night work and guard rings with rollers for edge work.

Main Manufacturers

Allen Engineering, a US manufacturer specialised in ride-on and walk-behind trowels.
Multiquip, with its Whiteman range of concrete finishing equipment.
Wacker Neuson, which produces walk-behind and ride-on trowels.
Husqvarna, with a range of concrete floor equipment.
Barikell and Bartell, known for concrete finishing machines.

Main Uses of Power Trowels

Industrial and warehouse floors with high flatness and wear resistance requirements.
Commercial and retail floors, car parks and public buildings.
Residential slabs, garages and basements.
Floors with dry shake hardeners, coloured surfaces and polished concrete finishes.
Elevated slabs in multi-storey buildings.
Repair and overlay work on existing floors.

Buying and Operating Tips

Match the machine to the job. Ride-on trowels are productive on large floors, but walk-behind machines are still needed for edges and small areas.
Timing is everything. Trowelling starts when the concrete can support the machine without deep marks. Starting too early damages the surface, and starting too late makes it hard to close.
Use pans for flatness. Floating with pans gives flatter floors than blades alone and helps incorporate dry shake hardeners.
Change blades progressively. Move from float pans to combination and finishing blades, increasing pitch and speed as the surface hardens.
Consider the weather. Wind, sun and low humidity speed up drying of the surface, while cold weather slows setting. Crews must adapt timing and may need additional machines.
Look after the machine. Blades wear quickly on abrasive concrete, and gearboxes, bearings and pitch mechanisms need regular inspection.

Safety

The main hazards are contact with the rotating blades, loss of control and exposure to exhaust gases, noise and vibration. Walk-behind trowels should have a safety switch that stops the rotor when the operator releases the handle, and guard rings must be fitted. Ride-on machines need operator presence switches and must be used with care near slab edges and openings. When trowels run with combustion engines indoors, carbon monoxide can build up to dangerous levels, so ventilation or electric machines are essential. Operators should wear hearing protection and use anti-vibration equipment where available, and wet concrete must be kept off the skin.

Trends and Technology

Power trowels are following the wider shift towards electrification and automation. Battery-powered walk-behind and ride-on trowels allow indoor work without exhaust gases and reduce noise. Remote-controlled trowels take the operator off the machine, and robotic trowelling systems able to follow programmed paths are being developed and introduced. Electronic blade pitch control, joystick steering and cruise control reduce fatigue on large floors. Floor measurement systems, linked to laser screeds and trowelling data, help contractors achieve the flatness required by high-bay and automated warehouses.

Key Terms

Floating: the first finishing stage, which embeds aggregate and levels the surface.
Trowelling: later stages that densify and smooth the surface.
Burnishing: high-speed final trowelling that produces a glossy, hard surface.
Pan: a round steel disc fitted under the blades for floating.
Blade pitch: the angle of the blades relative to the surface.
Dry shake: a hardener or coloured powder broadcast onto the surface and worked in with the trowel.

Frequently Asked Questions

When should a power trowel be used on fresh concrete? When the concrete is firm enough to support the machine and the operator leaves only light footprints. The exact time depends on the mix and the weather.

What is the difference between floating and trowelling? Floating levels the surface and brings up mortar, often with pans. Trowelling uses steeper blade angles and higher speeds to densify and smooth the finish.

Why use a ride-on trowel instead of several walk-behind machines? A ride-on machine covers more area per operator, applies more weight and produces more uniform results on large floors.

Can power trowels be used on polished concrete? Power trowels finish fresh concrete. Polishing of hardened concrete is usually done later with grinding machines, although burnished trowel finishes give a glossy result.

How many power trowels are needed for a large floor? It depends on the area poured, the concrete setting time and the weather. Large pours often need several ride-on machines working at the same time, plus walk-behind trowels for edges, so that the whole surface can be finished within the available window.