March 12, 2010

FOCUS | Concrete & Masonry

Accelerated schedules a challenge for vinyl flooring

PETER KENTER

correspondent

Vinyl adhesive manufacturers switched from products containing volatile organic compounds to water-based products in the 1990s. The change was good for installers and the environment, but not so good for some installations involving concrete floors.

While concrete grows in strength in the presence of moisture through hydration, that same moisture can re-emulsify water-based adhesives, destroying vinyl floors and lead to expensive remediation.

“It’s turned out to be a big issue with vinyl flooring, particularly sheet vinyl,” says Peter Waisanen, head of concrete technology with the Brampton office of engineering and consulting firm Trow Associates Inc.

“Unlike vinyl composition tile that has a joint every foot or so as an escape route for vapour, sheet vinyl has very limited opportunities for moisture to escape.”

When adhesive emulsifies, bubbles form under vinyl, and adhesive can seep out through joints.

“I’ve seen a hospital where the gurneys had quickly worn ruts into the vinyl,” says Waisanen. “The vinyl had to be removed at considerable expense. We’ve heard of instances where it occurs within weeks, and other instances where it occurs perhaps a year later.”

Waisanen says that water-based adhesives are often destabilized by moisture that wicks up through the ground.

“For moisture seeping upward, the problem is usually limited to slabs on grade,” says Waisanen.

“The problem can be solved by using an appropriate vapour retarder. The best place for that barrier is directly in contact with the bottom of the slab. We’re not talking about your typical six-mil poly.”

PETER WAISANEN, TROW ASSOCIATES INC.

Delamination of vinyl adhesive can result from contact with water that evaporates from concrete as it dries.

A vapour-retarding layer is usually placed on a stony, drainable material with workers walking on top of it, so there’s every chance for it to be punctured. You need to specify a high-strength, high-tear-resistant material to place on the sub-grades.”

Most vinyl suppliers require vapour-retarding barriers below the slab as part of the warranty, but Waisanen says that some contractors have a bias against them because they can cause curling around the edges of concrete pours. However, while curling can be mitigated with relative ease, vinyl adhesive problems can’t.

Adhesives are also destabilized by the water used as an ingredient in the concrete itself.

“Moisture will evaporate from the surface of the concrete,” says Waisanen. “With the use of a sub-slab vapour retarder, that’s the only place it can go. The important factor is determining when the slab is ready to accept water-based adhesive. Even with careful mix design and placement of an appropriate vapour retarder, it takes a long time to dry the concrete to an acceptable level.”

Many contractors measure concrete’s moisture vapour emission rate using calcium chloride. After 72 hours, the weight of water absorbed by the chemical represents the number of pounds of water vapour emitted per 1,000 sq. ft. per 24 hours.

“The industry has typically said that if that number is above three pounds it isn’t ready,” says Waisanen. “We don’t recommend that test because it only measures moisture from the top quarter-inch of concrete. We typically install a relative humidity probe to 40 per cent of the thickness of the slab. Once we get a reading of 75 per cent RH or less, we consider that the adhesive used for vinyl flooring will survive.”

However, compressed construction schedules are seeing owners and contractors demanding less time between casting of slabs and placement of flooring materials. The rule of thumb is that it takes one month for every inch of slab thickness to reach the appropriate dryness.

“If the contractor says there is no way they can wait that long, then you need to design a concrete mix with a low-water-to-cement ratio and that means compensating with additional chemicals,” says Waisanen. “Unfortunately that level of planning is not typical for the industry, yet.”

The adhesive problem is not just limited to new floors.

“I’ve even seen projects where they’ve taken off vinyl tile secured with a solvent-based adhesive to an old concrete slab on-grade,” says Waisanen. “When they install new vinyl using a water-based adhesive, the problems start.”

Mitigation measures can be disruptive and expensive. Waisanen says he’s seen successful mitigation with the use of an almost impermeable membrane applied to the slab surface by specialty contractors. Once installed, the barrier allows only a limited amount of moisture to exit the concrete, making it safe for vinyl installation.

Waisanen notes that the emulsified adhesive and moisture problem projects have little or no effect on the concrete itself. “It’s only the vinyl flooring that’s in trouble,” he says. “The concrete is only getting stronger.”

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