Tackling Walk-Behind Trowels

Power trowels can be used on larger concrete slabs requiring a floated or troweled finish. Typically these machines are used to produce a more densely troweled floor on concrete that is too stiff to otherwise handle utilizing manual tools. Compared to concrete hand finishing tools, power trowels significantly increase production and reduce costs by their ability to finish more square footage of a slab area per day. At the same time, they improve the quality of the concrete surface and help to maintain flatness on the slab.

There are a variety of walk-behind trowels to choose from on the market. Industry standard sizes range from 24-in. edging trowels to 48-in. models which are all used on a wide range of projects. Finishers working with hand tools can finish 300 to 1,000 sq ft per day, whereas using a 36-in. power trowel they can finish 1,000 to 3,000 sq ft per day depending on conditions. Besides the diameter size of a walk-behind trowel with most common being 24, 36 and 48 in., walk-behind trowels can also be divided into three categories.

1. General finishing – This is a good place for contractors that are just starting out or expanding their concrete business from hand tool finishing to power trowels. They will greatly increase their production time, reducing costs and increasing the quality of the slab.

2. High horsepower models – the added weight and power are especially suited for use during floating where higher torque is desired and is helpful in certain environmental conditions such as hot, windy weather.

3. Variable speed trowel – typically used by the contractor who needs a wide speed range (20-200 rpm), which is typical in industrial flooring applications.

Most concrete finishing jobs are based on size. Walk-behind trowels are best suited for smaller jobs like a residential basement floor and getting into areas where ride-on trowels cannot access due to architectural design or preinstalled plumbing, etc. However, applications for walk-behind trowels are far reaching from residential slabs and include commercial-industrial floors or use on high rise decks. Typically, a walk-behind trowel is a good choice if a contractor needs to finish less than 3,000 sq ft a day. Any contractor finishing more than that per day can justify a 36-in. ride-on trowel.

Job size, environmental conditions and if the jobsite is inside or outside should be considered when selecting a walk-behind trowel. For example, if the outside conditions are especially hot, dry and windy, some contractors prefer a high-horsepower model, which provides higher torque for low-speed floating while providing additional weight during the finishing phase. For cool weather finishing, smaller light-weight trowels become the finisher’s choice. For the professional who routinely finishes industrial floors, a variable transmission trowel provides a wide speed range for low speed, high torque floating through high-speed burnishing all-in-one machine.

A concrete mix that contains more than 3 percent entrained air should be finished by utilizing hand tools and not be given a hard trowel finish with a power trowel. If the entrained air content is higher than 3 percent, the floor can delaminate and cause problems in the finishing steps. Trowel selection has no influence on the concrete setting, however, knowing when the right time to begin power floating with a trowel and how to get started can influence the finish. A general rule of thumb for starting a first pass is when you can leave only a 1/8-in. deep footprint on the surface. Many variables affect this decision including the size and weight of the machine, the rate the concrete is setting, the speed and efficiency of the operator and the specifications of the particular slab.

The first pass should be with float blades, combo blades or float disks. Not all walk-behind trowels are suitable for pan floats; check with the manufacturer for recommendations. The blades should almost be flat with a slight pitch. Each consecutive pass should be followed by a waiting period and should be perpendicular to the previous one. This ensures a flatter floor. As the floor sets, combo blades or trowel blades are then used. The pitch of the blades should increase with each pass, which applies more pressure over a smaller area. For maximum productivity, beginners should consult with a local technical college or with a manufacturer who offers a training program for complete operation and finishing training before operating a power trowel.

Like any piece of construction equipment, contractors also need to consider a variety of features that contribute to performance, reliability and ergonomics. Many features are based on contractor preference such as the additional weight on higher horsepower models or the variable transmission for a wide speed range. Selection of pitch control, either dial up or lever activated, are factors to consider along with adjustable handle options, edging features, engine options and balance which enhances the overall feel of the machine to the operator.

Of course, operator comfort and ergonomics are extremely important for concrete finishers. It’s really all about production. The longer an operator can use a trowel without fatigue, the more productive he will be. Since the average age of a concrete finisher is approaching 48 years old, standing behind a power trowel is far less fatiguing than kneeling on boards all day finishing concrete by hand. Using a walk-behind trowel can typically take the place of one finisher for a particular job, freeing up a person to do other tasks and save money. A final note about safety: Operator safety is another factor to consider when reviewing walk-behind trowel options. Making sure that the trowel meets or exceeds industry safety standards is important and manufacturers are making great gains in this area.

Contractors should select a machine with a solid runaway handle stop mechanism and one that has a protective guard ring covering the rotating blades that meets all safety standards. Features such as these are especially important when new or less experienced operators are using the units.

Fred Paul is a sales engineering manager with Wacker Neuson Corp., based in Menomonee Falls, Wis.