Smooth Solutions
Power trowels are used for floating and finishing large concrete slabs that are too stiff to otherwise handle with manual tools. Compared to ordinary hand 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 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 600 sq ft per day, whereas using a 36-in. power trowel, they can finish 700 to 1,500 sq ft per day depending on conditions.
Besides the diameter size of a walk-behind trowel, with the most common being 24, 36 and 48 in., walk-behind trowels can also be divided into three categories. General finishing trowels are a good category 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. High horsepower models use added weight and power and are especially suited for use during floating where higher torque is desired and are helpful in certain environmental conditions such as hot, windy weather. Then there are variable speed trowels, which are typically used by the contractor who needs a wide speed range (20 to 200 rpm), typical in industrial flooring applications.
Most concrete finishing jobs are based on size. Walk-behind trowels are best suited for smaller jobs and getting into areas where ride-on trowels cannot access due to architectural design, preinstalled plumbing or some other reason. However, applications for walk-behind trowels are far reaching from residential slabs and include commercial-industrial floors or use on high-rise decks. A guideline that can be considered is that if a contractor needs to finish less than 3,000 sq ft a day, a walk-behind unit is a good choice. Any contractor finishing more than that per day can justify a 36-in. ride-on trowel.
Beside the size of the job, environmental conditions and location of the jobsite (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 using hand tools and not be given a hard trowel finish with a power trowel. 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 effect 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. Consecutive passes should be made perpendicular to the previous one. This ensures a flatter floor. As the floor sets, the pitch of the blades should increase. 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 is 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 or she will be. 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.
Big Choices in Small Pumps
Rock Reed, Vice President of the Honda Power Equipment Group
The right equipment on a jobsite can make the difference between successfully completing a water or sewer line, storm drain or pump station project or facing costly delays. This means that contractors must carefully evaluate a number of factors when choosing pumps for construction applications and maintaining the service lives of the models they depend on.
Whether it’s a pump for water or chemicals, one of the most important considerations is choosing the right model for the right application. Let’s start with the basics. Most general purpose de-watering pumps are for moving relatively clean water. Construction — or trash — pumps are used for pumping water contaminated with sticks, leaves, stones and other waste materials. Multi-purpose pumps move water as well as a variety of agricultural and industrial chemicals. Finally, submersible pumps are used for a wide range of residential and commercial sump applications.
Before using the pump, the operator should check the oil and air cleaner, confirm all the hoses are properly connected and fill the pump chamber with water. Other maintenance checks include periodically changing the engine oil, cleaning the air filter and occasionally replacing the spark plug. To ensure the pump maintains maximum performance, the impeller (a rotating component which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation) should be inspected for wear once a year or more often when pumping water containing abrasives. When pumping salt water or water containing silt or mud, the pump should be flushed out with clean water after each use to prevent excessive corrosion or silt or mud buildup in the pump case. The operator should always refer to the owner’s manual maintenance requirements specific to his or her pump.
The pump’s impeller, volute (a curved funnel that reduces the speed of the liquid and increases the pressure of the liquid) and mechanical seal are subject to wear when pumping water containing abrasives (i.e. sand). This wear eventually can result in reduced pump output and increased priming time, or in severe cases, the pump will not prime. The cost will vary significantly among models as well as from the extent of wear. Inspecting the impeller each year will help avoid excessive costs and the inconvenience of an unexpected failure.
