Tackling moisture issues on concrete subfloors

Home Featured Post Tackling moisture issues on concrete subfloors

moisture issues humidity meter
There are various testing methods for assessing moisture conditions. Using humidity meters in accordance with ASTM F2170 is one of them.

By K.J. Quinn Moisture issues in concrete slabs remain a serious installation bugaboo, contributing to floor covering failures costing an estimated $1 billion to mitigate annually, reports say. While not common to all jobsites, experts say installers can reduce damages by tackling any potential problems before new flooring is laid down.

“Moisture issues have become very widespread due to job deadlines being pushed tighter and tighter, causing the concrete to not have time to cure properly before the flooring is scheduled for installation,” noted Wayne Williams, Stauf USA’s director of training.

Most moisture-related flooring failures happen with non-porous floor coverings such as hardwood, LVP/LVT, resilient sheet goods, etc. Even carpet backings designed to prevent top-down moisture from reaching the substrate can fail from excessive moisture vapor emissions. “Moisture becomes trapped underneath the flooring without a means of escape,” explained Shane Jenkins, senior technical coordinator, Schönox. “This requires better control of moisture content within the concrete before it reaches the top surface.”

Demand for moisture-sensitive flooring such as resilient is reportedly on the rise, making it imperative to address any moisture concerns early in the construction process. “High moisture and the high pH associated with it in concrete substrates are the most common causes for flooring failures,” said Gary Scheidker, director of technical services, Taylor Adhesives.

In commercial installations, resilient flooring is especially vulnerable when laid over concrete surfaces. “The most common issue is blistering, seam opening, lifting and adhesive re-emulsification under sheet vinyl and LVT/P,” said Jeff Johnson, business manager for floor covering installation systems at Mapei. “Carpet tile, on the other hand, gets its share of moisture-related problems also in commercial environments with cupping and adhesive re-emulsification.”

In the residential market, engineered and solid hardwood floors installed over concrete substrates are the most susceptible to moisture-related issues. “The only flooring type that seems to be resistant to moisture issues is ceramic tile,” Johnson said. “But even there, excess moisture can cause problems.”

Early detection is key

The concerns over moisture mitigation have grown significantly as condensed construction timelines increase in frequency. “In most cases, issues within the concrete itself are caused by installers being rushed to build onto the slab before it has fully dried,” said Mitch Hawkins, Laticrete’s senior manager, technical services. “Moisture issues can often be avoided by allowing the concrete slab to properly dry, under the right conditions, before continuing work.”

Installers learn early on about the importance of testing for moisture content before opening the first bucket of glue. “This should be done long before the installer arrives to actually install the flooring,” Stauf’s Williams said. “So, if there is a moisture issue, it can be addressed with the general contractor and a decision can be made.”

What has changed over the years is the installation community has grown more sophisticated, observers say, moving away from testing at the last minute. “Proactively addressing moisture mitigation can be done in the design process,” Schönox’s Jenkins noted. “This includes third-party testing and inclusion of a moisture-mitigation system in the project specifications.”

In most cases, moisture issues are not visible until a moisture-sensitive or non-porous floor is installed. “In some cases, this makes it difficult to explain the additional time and cost involved for moisture control,” Taylor’s Scheidker said.

Often overlooked for moisture in concrete is condensation, commonly referred to as “sweating slab” syndrome, according to David Seland, principal, ISE Logik Industries. “Is it really moisture coming from that concrete or just that moisture in the air above the concrete hit the dew point and condensed on the concrete surface?”

There are various approaches and testing methods used to assess moisture conditions on a concrete slab prior to installation. Two recommended methods are Calcium Chloride MVER (ASTM F-1869) and RH (ASTM F-2170).

Nearly all technical data sheets for flooring installation materials contain some verbiage about qualifying the concrete slab for moisture levels before using the products. “Visually, an installer might be able to determine if a concrete slab has moisture problems by looking for dark areas, or areas covered with white salts—which is indicative of massive moisture migration and salt deposition on the surface,” Mapei’s Johnson explained. “But using your eyes is not a valid test method.”

The telltale signs are liquid buildup under the floor and emulsified adhesive. “They will see residue oozing up between the seams, the curling of the flooring, blisters and so on,” Johnson added.

Even after proper testing, there’s no guarantee moisture conditions will remain constant on the jobsite. “The key thing to remember is a moisture test is not a predictor of what’s going to happen in the next 60 seconds, let alone next week or next year,” ISE Logik’s Seland said. “If you have to put down a moisture-mitigation system, use something that is warranted and can operate in a 100% relative humidity situation, so you know it will work 100% of the time.”

An ounce of prevention

moisture mitigation Schonox quick-dry
An installer applying Schönox’s quick-drying, moisture-mitigation system, EPA Rapid.

Moisture mitigation is not overly complicated when instructions are followed properly, experts say. But it does take time to treat the subfloor. This can impact timelines for most projects, many of which are developed assuming the concrete slab will be dry and ready for flooring installation.

In addition, moisture mitigation costs can be as much or exceed flooring materials and installation. Mitigation systems can be as much as $5-$6 per square foot. “This could include surface profiling, in addition to moisture mitigation, as well as adding days to the project completion,” Stauf’s Williams noted.

Installing a moisture mitigation system requires several steps. For starters, concrete surfaces need to be pristine, porous and textured for most systems to work properly. “You cannot place them over old adhesive residue, and you cannot use them to hide the problems of the past,” Mapei’s Johnson advised. “The contractor does have to spend some time getting the floor cleaned up and ready to accept the mitigation product.”

There are myriad moisture mitigation systems, each offering different advantages when it comes to performance, application time and installer friendliness. The different methods are dependent on the level of moisture and ability of the subfloor material, flooring and adhesive to resist moisture. “Simple methods like acrylic-based systems are user friendly and simple to use,” Schönox’s Jenkins said. “Two-part epoxy systems offer the highest degree of moisture mitigation and protection.”

A common method is treating the concrete slab with a resinous or epoxy coating, specifically designed and manufactured for that purpose. As Laticrete’s Hawkins explained: “This minimizes moisture vapor emissions from transpiring through concrete and affecting adhesives used to bond the finish floor material, potentially raise the humidity in the room and possibly increase the occurrence of mold, mildew and other moisture-related problems.”

Costs associated with different methods and systems are dependent on the products used, type and size of the application. Experts say installers should consult the manufacturers about the products they wish to use prior to installation. “This step will easily save contractors headaches later down the road, when costly repairs may ensue from improper choices,” Hawkins noted. “Using one manufacturer as a single source of materials for a complete system can also be a great advantage and offer peace of mind to ensure product compatibility and full systems warranties.”

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April 12/19, 2021

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