Anyone who’s been through the construction process has heard the words “moisture mitigation.” While it’s not new, concern over the issue has grown over the last 10 years.

One reason is condensed construction timelines, which mean most projects are fast-tracked, leaving less time for concrete slabs to dry. This leaves slab moisture levels (relative humidity or RH levels) at unsuitable levels for flooring installations to perform. However, these levels must be met in order to maintain a manufacturer’s warranty.

Another issue is the shift to more sustainable materials and building practices. Josh DiGloria, senior project manager, Suffolk Construction (Boston) says in an effort to go green, flooring manufacturers have replaced some of the toxic chemicals in their glues with more water-based ingredients. “The concrete mixtures originate from limestone and have calcium silicate components within the final slab product, and when you put the flooring adhesives on the concrete slab and then put rubber flooring directly on top, the water vapors will move thru the slab and interact with the glue,” he says. “So a lot of hospitals and health care projects that use rubber have seen failures in the rubber adhesion bonding to the floor, which create bubbling or floor section peeling up.”

Finally, the composition of the concrete itself can be an issue. Jennifer Mango, interior designer, at TSOI/Kobus & Associates (Cambridge, Mass.), says concrete is specified in an array of mixes that are customized to the application, and when ingredients are added, that alters the concrete’s dry time as well as its physical characteristic, which impacts the adhesive’s ability to bond.

The key to addressing these problems is planning. “Before you actually put the concrete slab into the project, you have to have a plan for how you’re going to solve the moisture mitigation,” DiGloria says, “and the cost of the plan has to be included in the budget.”

Mango says some project choose to “wait it out” with a budgeted moisture mitigation contingency. Then when the flooring is ready for install, a moisture test is conducted to get a relative humidity (RH) reading on the slab. If the level is low enough, the installation can move forward. If not, a moisture mitigation system is required, which means premium costs and schedule delays. “The reality is that moisture mitigation is almost always required,” she adds.

Here are some options to consider:
1. Topical applications: After the concrete slab is set, a PH blocker coating is applied to the slab, which prevents moisture from seeping up. DiGloria says the cost for this procedure could be up to $4 per square foot, which can add up quickly, so one consideration is adding the coating before the walls go up to reduce labor costs and time.

As part of this process, DiGloria says he sandblasts the concrete to ensure the moisture blocker adheres properly into the concrete layer. However, glues might not adhere to this glossy/smooth coating, so once the PH blocker is applied, the flooring contractors must come back and add a skim coat product on top to ensure adhesion with the glue. “So it’s actually four steps, and that’s part of the cost, since you have to have the installers make multiple trips over the same area the labor hours add up,” he says.

2. In situ treatment: This admixture chemically alters the concrete mix to eliminate moisture vapor emission through the slab. Manufacturers that sell these compounds mix them at the concrete plant. These products are relatively new to the market, so there’s a lot of competitive price bidding that’s making them an attractive option. The downsides, however, are that steps need to be taken to address quality control standards and assurances, including a review process of concrete compounds, strict supervision of mixing, and flooring adhesion and bond testing. DiGloria also suggest a light buffing on the top of the slab to ensure the glue will adhere to the slab.

In the end, project partners needs to have a discussion early on to weigh scheduling, impacts, and cost options. “The only rule is you have to plan something,” DiGloria says.

For more on flooring, check out Healthcare Design's trend piece in the May/June issue.