Concrete floor slabs contain excess moisture that can damage many types of floor finishes. To address this problem, contractors use a variety of products and techniques developed to mitigate the moisture and prepare the surface for proper flooring installation.

Here are two examples of subfloor problems and the solutions contractors used to complete successful installations.

Penn State South Halls Renovation

What do you do when you’re a respected institution with a focus on environmental responsibility and you find yourself confronted with renovation projects that involve asbestos and deteriorated subflooring?

Penn State University tackled the issue by turning to Nittany Building Specialties, a commercial contractor based in Port Matilda, Pa., which recommended Spartan Surfaces and three HPS Schönox products.

The Penn State South Halls project encompassed the renovation of four residence halls originally constructed in 1956, the construction of one new residence hall, and the external and internal renovation of Redifer Commons, a shared space for students.

Much of the existing space was originally covered with adhesive and tiles containing asbestos. While those materials had been removed with chemical remediation, many tile and adhesive manufacturers would not warrant the installation of their products over remediated surfaces. In addition, the concrete subfloor was pitted with valleys and high spots. Having undergone an asbestos abatement process, the substrate had residual chemicals within it leading to warranty issues with the proposed new flooring installation. In addition, the concrete subfloor was uneven with pits, valleys, and high spots throughout the space.

A series of Schönox products were specified that would address the substrate challenges, according to Dave Lepird, Schönox vp of business development. Schönox EPA two-component epoxy-based moisture mitigation system provided the solution for covering the chemically abated substrate. The product is suitable on porous, unheated concrete slabs to reduce moisture vapor emission rates from 100% RH or 25 lbs./1000 sq.ft./24 hrs to suitable levels before applying Schönox underlayments. Only one coat required to penetrate and to fully seal the substrate. Schönox EPA was applied with rollers directly to the concrete substrate and the chemical abatement contaminates were sealed below.

Schönox SHP special acrylic primer was applied with a roller on top of Schönox EPA, providing a surface that bonded well with the self-leveling compound. Schönox SHP contains no volatile organic compounds and dries in one to two hours, according to the company. Schönox AP synthetic gypsum self-leveling compound was poured throughout the space providing a smooth, level surface. Special dust-reduced properties kept dust to a minimal level, and Schönox AP does not shrink or crack.

The renovated subfloor was ready for luxury vinyl tile flooring installation in less than 48 hours, and both the tile and adhesive manufacturers fully warranted the new installation after the subfloor preparation process was completed.

Hospital Project, Virginia

Cherry Carpet & Flooring based in Portsmouth, Va., has faced its share of subfloor issues due to moisture.

“We constantly have moisture issues here,” said Ross Cherry, president of Cherry Carpet & Floors. “We have rising sea levels here in Norfolk, and we’ve had some failures in the Chesapeake area where, if you look at the satellite maps, it is filled-in marshland.”

Cherry has more than 20 years of experience in the flooring industry and he said most of the company’s projects require moisture mitigation. One repeat customer he uses as an example is a hospital the company has worked in since 1998, which became a case study for moisture mitigation.

“We were doing the ER and we were measuring 98%RH [relative humidity],” Cherry said. “We explained the problem to the facility manager and what it was but he signed off on it. It was an MRI [magnetic resonance imaging] unit and it failed in six months.”

The hospital then proceeded to replace the floors in the emergency rooms, but calcium chloride tests showed water dripping out of the petri dishes. “That was one of the first larger floors we moisture mitigated back in 1998 and 1999,” Cherry said. “The discussion then was your ER failed and you know what moisture is.”

Fast forward to today, with a new facility manger and the same moisture issues on an 11,000-s.f. project. The team went through almost two years, 12 different flooring designs and countless products and colors before they started moisture testing. It failed with 98%RH.

“We set a price for about $44,000 to moisture mitigate and we were already planning on grinding the floor,” Cherry said. “They had an area of old terrazzo that had a lot of movement and moisture coming through the joints and telegraphed a grid under their existing floor, so they wanted a guarantee that it wouldn’t happen.”

Cherry said pricing for moisture mitigation is dictated on whether the project is new construction or renovation, what floor the crews are working on, and what they have for electricity to grind open the concrete. “It can range from $2.50 to the high end of $5 per square foot,” he said.

In the hospital, Cherry’s team ground the terrazzo and partnered with Schönox to use the company’s moisture mitigation products to seal the moisture using EPA and primed the floors using SHP. After priming, the team then used APF self-leveling system over it at ¼" thick. The fiber reinforced gypsum material was used to allow slight movement in the terrazzo underneath if it occurred. The team then installed the Centiva Floors with Schönox Roll and Go adhesive to finish the complete system. Schönox guaranteed the floor for 10 years.

Cherry said if the hospital had decided to forgo the moisture mitigation this time he would have walked away from the project. “With our logo all over the project and as many people as walk through those buildings, I was not willing to take the risk,” he said. “It’s a win-win story now. It’s an absolutely beautiful floor. It took about a year to do the whole thing through night work and various phases, but we are getting ready to do the second and third floors with the same product, which won’t have to be moisture mitigated, but they do want to use the same leveler.”

The Portsmouth team has gleaned several takeaways from their years of experience battling moisture.

“The lessons learned, without a shadow of a doubt, is to get all the existing and old patch leveler off the ground,” Cherry said. “The only failure I’ve ever had is when we’ve missed an area, but the failure was extremely small—a 5' x 5' area that blew up and we had to cut out the sheet vinyl.” Thankfully, the property owners still had sheet vinyl from the same dye lot, so the repair wasn’t as bad as it could have been.

One of the other issues they have discovered is trenches. “I’ve found in trenching is that it’s done by the cheapest labor on the jobsite if there’s not a flooring or concrete sub,” Cherry said. “Most of the time they over wet them and they never put a primer on the side, nor do they put a slurry coat on there to make sure they get a bond.”

Contractors get two issues in trenches: one is that they over wet it so your capillaries in the concrete end up creating a very porous concrete, which also brings up latency to the surface.

“I’ve had failures on a couple of trenches where we’ve bonded to concrete and bonded to the surface but the surface was latent, and once the water started pushing you can’t hold it because the surface was so weak from all the minerals and things that come up with it,” Cherry explained. The other failure you’ll see is at the bond of the new concrete to the old concrete; when it’s over wet you get shrinkage and you get areas of vapor that move quickly and create failures.

“We grind all of our trenches and the top layer is taken off to make sure we get a good stable surface,” Cherry said. “We also treat all of our trenches with epoxy. No matter what they say, the vapor barrier is not bonded properly. The seams from the old concrete to the new concrete are not done with a primer, so you get these tiny open veins in them where you get failures. So, we coat 9 inches on the sides of trenches and we grind new old concrete and use a two-part moisture mitigation on that surface.”