For the construction of floors of significant size, riding trowels have become indispensable. They are productive and can provide very flat finishes. The two types of machines on the market are overlapping and non-overlapping. The troweling patterns of overlapping machines intersect one another and are especially suited for trowel finishing, but you can't install float pans on them. Non-overlapping machines have a space between the rotors, making it possible to mount float pans for initial floating operations and then switching to trowel blades for final finishing operations.
What to look for when buying a machine
Here are some suggestions from Tom Caterina, quality assurance and project manager for MultiQuip-Whiteman, Boise, Idaho, about what to look for when you are considering buying a troweling machine:
- You can purchase 6-foot, 8-foot, or 10-foot machines (rotors are half this size). There are many factors that affect floor flatness (FF), but generally, the larger the machine, the easier it is to produce high FF floors.
- Look for driving mechanisms that allow for “back-shifting”—continuously variable transmissions (CVT) that allow the engine to operate at full speed while the trowel gears down to handle the load in difficult areas.
- Deciding how much horsepower to have is important, too. Machines must be able to provide adequate power to the rotors and still have enough to provide speed for the machine. Weight-to-power ratios are often used to compare machines.
- Weight is important. Generally, the heavier, the better because you can wait longer before beginning finishing operations, allowing for a flatter floor. Machines weigh from 900 to 2200 pounds, not counting the weight of the operator.
- There should be easy access to the top of the rotors for removing bolts during blade changes.
- You can purchase machines with either manual or hydrostatic driving systems. Hydrostatic systems reduce finisher fatigue, but some finishers think that mechanical steering systems provide a better “feel” for floor conditions.
Basic finishing steps
Finishing concrete is both an art and a science. Aside from the quality of equipment used, it's the finisher who decides when finishing operations should start and what to do when problems arise. More than equipment, their skills determine the flatness and finish of a floor. Bob Simonelli, floor finishing consultant, Structural Services Inc., New Smyrna Beach, Fla., offers these suggestions about the basic steps for finishing floors.
You should start the first floating operation when you can barely see your footprint on the fresh concrete—your footprint shouldn't depress more than 1/8 inch in the fresh concrete. Simonelli says that approximately 90% of finishers use float pans today for normal floor installation work. Specialty floors, such as floors with surface hardeners or trap rock, sometimes require different techniques. You can also judge whether you are starting finishing operations at the right time by the height of the “wind rows” between the float pans, which shouldn't exceed ½ inch.
Typically, at least three passes are made with float pans before troweling operations begin. Make the first pass at a 90-degree angle to the line of the strike-off. The second pass should be at 90 degrees to the first pass. And the third pass should move in a direction diagonal to the other two. Simonelli advises moving the machine in a backwards direction over slab edges to reduce edge build-up.
After floating with float pans, Simonelli likes to make a couple of passes with combination blades before starting troweling operations. This “lays the floor in,” creating the best conditions for final troweling operations. There should be at least four passes with trowels starting with low blade angles on the first pass, increasing the angle with succeeding passes as the slab gets harder.
As a general principle, the more surface contact there is between float pans and the concrete, the higher will be the FF of the slab.