Anyone who works in multistory commercial construction and renovation knows the concrete slab usually isn’t perfectly level across a floor’s entire span, requiring some sort of remediation before finish flooring can be placed.
Grade differences in the slab between the curtain wall and structural components are usually eliminated with self-leveling material. That, however, was not an option for the flooring subcontractor helping to renovate a 17-story New York City office building.
Part of a national network of universities and companies that collaborate to develop and commercialize medical technologies, the building houses laboratory and office space, equipment, and other amenities.
One such amenity is an employee gym consisting of yoga, dance, and strength training studios, which require different elevated flooring systems. Differences between subfloor elevations and flooring system thicknesses had to be eliminated for the floors to align.
The project’s architect ruled out placing self-leveler over the entire area to raise and level out the slab. Combined with heavy weightlifting equipment in the strength-training studio, the material would exceed building design weight limits.
Instead, New York-based contractor Consolidated Flooring was tasked with forming and placing a series of curbs – similar to the raised concrete barriers that delineate parking spaces on streets and in parking structures – on the slab to act as support joists. Instead of a uniform trapezoid, though, these curbs would be rectangular and vary in height and length as necessary to raise the entire subfloor to the proper elevation.
New Product Meets Contractor’s Needs
Consolidated Flooring is a third-generation commercial flooring specialist that has expanded from New York to Florida, Illinois, Indiana, and Texas over the last 80 years.
The company has used Rapid Set® LevelFlor® self-leveling underlayment and Rapid Set® TRU® polishable overlays for more than a decade to quickly deliver aesthetically pleasing and highly durable floors in high-traffic areas such as lobbies, hallways, showrooms, and cafeterias. In fact, crews were placing TRU® PC (for “polished concrete”) on the building’s 16th floor when the issue with the gym subfloor arose.
The company also uses Rapid Set® products to repair substrate damage before moving on to the next stage of a job. Cement All®, a multipurpose concrete repair material that can be applied from featheredge to 4 inches and achieves structural strength in 1 hour, is one of the contractor’s go-to solutions for patching and other repairs.
The architect’s specified remedy was a rather unusual application, however, and Consolidated Flooring’s crew was apprehensive about Cement All’s 15-minute set time. Would that be enough working time to fill and finish 6-inch-wide forms ranging in height from 0 to almost 6 inches placed every 2 feet on center? The existing slab was 3 ¼ inches out of level from the highest to lowest point and, in some areas, the crew would have to add up to 2.5 inches to curbs to bring the subfloors to the same elevation.
Ben Graham, northeast regional manager for Rapid Set® producer CTS Cement Manufacturing, recommended using Cement All® Plus instead of Cement All®. Cement All® Plus also can be applied from featheredge to 4 inches thick, but has a longer working time and is self-curing. When time is of the essence, as it was here, crews don’t have to keep exposed surfaces wet for at least an hour.
After mixing and working with sample material supplied at Graham’s request by White Cap Construction Supply, Consolidated Flooring got the architect’s approval to use Cement All® Plus.
Subfloor Restored
TRU® self-leveling overlays are placed on profiled substrate that’s received an application of TXP™ Fast (ready for overlayment in 4 to 6 hours) or TXP™ SuperFast (ready for overlayment in ~ 2.5 hours) epoxy primer followed by sand broadcast to refusal.
Rapid Set® repair products, such as Cement All® Plus, don’t typically require a bonding agent. However, because Consolidated Flooring was placing TRU® overlays on the same floor and had the supplies on site, they decided to apply the epoxy-and-sand broadcast on the substrate.
After building and placing the forms, the crew added water to the Cement All® Plus powder, tweaking the mix with Rapid Set® FLOW Control® to increase fluidity or Rapid Set® SET Control® to extend working time as needed. They poured the mix into the forms and hand-troweled them off. They used more than 780 55-pound (25-kg) bags of Cement All® Plus on the project.
Cement All® Plus achieves 4000 psi (27.6 MPa) compressive strength in 3 hours.
“This was definitely a different process than we’re used to,” says Consolidated Flooring Project Manager John Drago. “But it worked out and the product is great.”
