Residential high-rise construction in New York City is typically concrete frames and flat-plate slabs that go up at the astonishing rate of a floor every two days. The pressure of the two-day cycle means that concrete contractors welcome ways to increase productivity—not corners to cut but ways to achieve the same result more quickly. Today, one of those techniques is placing self-leveling toppings on floor slabs.
“We just screed the floor and leave it,” says Ron Ferrari, president of SBF Construction, Hackensak, N.J. Pyramid Floor Covering then arrives as soon as seven days after concrete placement and pumps a self-leveling underlayment onto the floors. “The owner is ecstatic that everything is moving so quickly,” says Ferrari. “And the flooring guys are happy because they have an excellent substrate for their floor. It’s a wonderful system—there are simply no negatives.”
For years concrete contractors and flooring contractors have battled over the different floor flatness requirements in Division 03 and Division 09. The F-numbers specified in Division 03 are what concrete contractors go by while the flooring installer insists on the 1/4- or 1/8-inch in 10 feet specification of Division 09. Concrete contractors are required to measure within 72 hours and while the shores are still in place and not at joints or near penetrations. But although that is fair for the concrete contractor, weeks or months later when the flooring installer arrives, the floor has deflected with removal of the shores and could be curled at the joints. This can make installation of hard flooring and interior fiishes and fixtures difficult or impossible.
There’s also the issue of moisture within a concrete slab. Any impermeable flooring materials adhered to a concrete floor requires the slab to dry out first, which can take months. Low water mixes help, but troweled surfaces can increase drying time and throw off the schedule.
Using a self-leveling underlayment, though, especially in combination with a moisture-mitigation system, solves both of these problems. The concrete contractor simply leaves the floor about 3/4 inch below the specified finish elevation and screeds it off. “It’s the only way to make money on slab on metal deck jobs,” says Tommy Ruttura, Ruttura & Sons Construction, West Babylon, N.Y. “We screed it, then broom it, and get out. It’s much more productive.”
For floors that are truly fast-track, the contractor installing the underlayment starts by applying a moisture mitigation system—an epoxy-based coating that prevents moisture from moving through the concrete surface. On floors that have been allowed to dry to about 95% internal relative humidity, this step masy not be necessary. On existing floors or floors that have been troweled, a shotblasting step may be needed to get the floor to about a CSP 3.
In some cases the underlayment may be installed directly over a sand-boradcast epoxy and in others a primer may be installed, sometimes a diluted version of the underlayment material with polymers to assist in penetration into the concrete substrate and to increase the bond of the underlayment.
The underlayment can be installed as thin as 1/8 inch and up to several inches. The ideal underlayment material, according to Stephen DeGaray, president of Pyramid Floor Covering, is a low alkali formula that acts like an alkalinity barrier, creating a better environment for flooring adhesives. “We use level pegs to know how thick to place the material,” says DeGaray. These are placed every 4 to 5 feet and positioned using a water level.
The material, with the consistency of pancake batter, is pumped out and spread and smoothed with rollers. “As in all underlayment applications, we tell installers to use plastic baseball cleats to walk in the material,” says Ben Mack, director of marketing for Ardex. “The material will heal around the cleat marks. We don’t recommend metal spikes because they could damage the primer coat.”
About 15 years ago, DeGaray was installing self-leveling underlayments in New York using bagged materials, but he had an idea for a better way. Today, that better way is Laticrete Supercap. In 2012, Ardex introduced a similar system they call the Ardiflo System. These self-contained truck/trailer systems include a knuckle-boom crane to load one-ton super-sacks of underlayment material into a hopper and a mixing pump that delivers the underlayment to the floor inside the building.
This has lots of advantages. The traditional way to install underlayments is to mix bagged materials and place them in small batches. With the new truck systems, the underlayment can be installed with very few workers and no equipment or bags of materials being moved into the building. There’s no dust, no mess, and little noise. And the super-sacks eliminate the waste and inefficiency of 50-pound bags.
“This greatly speeds up the installation,” says Mack. “This process is basically cost-neutral but it saves time and money overall and the expected smoothness, levelness, and moisture control are achieved so that when the flooring is installed later in the project there are no unexpected issues to deal with. We are not promoting a cost savings but rather an alternative to offer a specified, scheduled, and budgeted outcome with guarnateed flatnes and dryness.”
Both systems use a calcium aluminate material that has very low shrinkage yet hardens quickly—within a few hours—and flooring can be installed in 24 hours. This material “is very easy to pump,” says DeGaray. “We can easily pump it 20 stories high at 50% to 60% less pressure than for concrete. We’ve pumped as high as 68 stories with a two-stage pump.” The Laticrete Supercap truck pumps 30,000 pounds per hour, enough for about 15,000 square feet of floor.
The Ardex system has two sizes and styles of set-ups. The Cube is the mid-sized system and is mounted on a goose-neck trailer that can be pulled with a pickup truck. The PowerFlo is a larger unit on a self-contained trailer pulled by a semi-tractor. These units are also equipped with a crane, material silos, a super-sack loading cutter, and a high-volume mixer pump. The Cube can provide enough material for about 10,000 square feet per hour, while the PowerFlo can deliver 16,500 square feet per hour in a 1/4-inch topping. The Cube pumps 150 feet vertically and 400 feet horizontally and the PowerFlo even further.
“We have Pyramid install Laticrete Supercap on every job,” says Ferrari. “Trying to reach the stringent tolerances in the spec is virtually impossible, especially on a two-day cycle—there just isn’t enough time. We’ve used this system on many high-profile jobs around the city, from Mercedes House to the Empire State Building. I wouldn’t do a job without it.”