How flat can you make a floor?

If you're part of the Webcor Concrete team at the Santa Clara Valley Medical Center (SCVMC) project, the answer is: flatter than ever before.

On one section of the project's third level, covering about 20,000 square feet, the floor flatness measured 65, a Webcor record.

"Concrete floor flatness is a process our finishers achieve," says Dennis Heimer, construction manager for Webcor Concrete. "The process begins with making sure the floor is at the right elevation; then you run troweling machines over it to produce the degree of flatness." While different projects specify different flatness requirements, Webcor finishing crews typically deliver flatness ranging from 35 to 55. "Fifty-five is really good," Dennis says, adding that raising the bar to 65 goes well beyond that.

The level is assessed by a machine that tests the floor for inconsistencies after completing a pour.

Flatness matters because, Dennis explains, waves in the concrete -- which could be invisible to the naked eye -- can affect finishes. For example, a flooring company could face extra work to achieve the degree of flatness necessary for the carpeting or other flooring material they need to install. It can also impact how other finishes fit, such as door frames and hardware. "Bad floor flatness can have a lot of repercussions," he says.

Dennis would have praised Concrete for achieving a flatness level of 55 at SCVMC. "The difference between 55 and 65 isn't huge, but it's enough for me to take my hat off to the finishing crew. They put as much care as possible into their work, setting the bar really high. And in doing so, they reached heights we've never reached before."

At least, Dennis can't recall getting to 65 on a structural steel facility, nor, he says, could Webcor Craft Executive VP Chris Plue when they were discussing it.

"We have been doing things on this job I've never done before on a structural steel building," Dennis adds, all in pursuit of maximum flatness. For example, steel beams used in the medical center have a crown in the middle. The weight of the concrete poured over them is supposed to flatten the crown, "but there are a lot of variables that can affect just how flat they get." As a result, floor level requirements are typically not critical. "But here, they were in the specs, so we held to them."