It is tough to argue that moisture control is the most important aspect of any installation. If a concrete slab’s moisture content is not at acceptable levels, the installation will fail, each and every time. Following are some of the tools and techniques to help ensure that an installer or contractor keeps within moisture limits, and what to do in case of a moisture emergency.


Testing the slab

Testing the moisture content should be the initial step of any installation. All concrete will have vapor flowing through it; the trick is to keep it at acceptable levels. For years, calcium chloride tests (ASTM F1869) were the standard for checking moisture, but this is slowly changing to relative humidity testing (ASTM F2170). The problem with calcium chloride testing, according to Homer Taft, Dependable Chemical Co.’s president, lies is what the test actually measures.

“It generally reports what is occurring at the concrete surface, whereas relatively humidity testing can report the potential for future problems from deeper in the slab,” he said. “However, there may be circumstances where a relative humidity test cannot report the required information, such as what emissions are occurring through a membrane. In that case, a modified calcium chloride test may be the only alternative.”

Either test requires certain conditions to be met. It may also acquire an adjustment of expectations: Moisture levels taken at the time of the test should not be assumed to remain the same for the life of the installation. For this reason, it is important to know what is causing any moisture problems so the source can be addressed. “Understand as much as possible about the nature of the slab construction, service use over time, and the source of the moisture,” Taft noted.

Additionally, the HVAC system in the building needs to be running and the area needs to be given enough time to acclimate to the conditions of actual usage. Otherwise, the test results will likely be inaccurate. As Jim Gourley, owner of Bone Dry Products, noted, “I see too many occasions where the testing preparation is not done correctly and the readings are basically worthless. Proper procedures are critical in determining accurate moisture levels.”

Leigh Hightower, MAPEI’s U.S. technical services manager, stressed the importance of following whatever test is chosen to the letter. The calcium chloride test requires scarifying and cleaning a 20” by 20” area of concrete and letting it acclimate for 24 hours. Then a Petri dish containing carefully weighed calcium chloride granules are placed under a plastic dome covering one sq. ft., and the dome is sealed to the concrete. This assembly must be left in place for from 60 to 72 hours, after which the Petri dish is weighed. That weight is used to calculate the Moisture Vapor Emission Rate or MVER, which is a measurement of the moisture vapor (in pounds per 1,000 sq. ft. in 24 hours).

The relative humidity test requires a hole drilled into concrete at a depth of 20 to 40 percent the thickness of the concrete slab, depending on whether the slab is drying from the top and bottom or the top only. A probe sleeve is inserted into the hole and sealed. Electronic probes are then inserted into the probe sleeves and allowed to acclimate. This measures the relative humidity of the air space at the bottom of the probe sleeve.

Both tests have their limitations, Hightower noted. “F1869 [the calcium chloride test] can tell you what the MVER flow is but it cannot tell you how much moisture is in the concrete slab at the time. F2170 [the relative humidity test] can tell you how much moisture is in the concrete at the time of the test, but it cannot tell you how fast it is flowing. Neither test can tell you if there is moisture entering the concrete from an outside source such as a breach in the vapor barrier beneath the slab or from plumbing leaks within the concrete.”

A third type of test is also widely used: Non-invasive testing with an electronic moisture meter. This type of testing can be a great complement to the relative humidity or calcium chloride tests, but should not be the only test performed. “Non-destructive or non-invasive testing is the quickest of the test methods and can give some very useful information,” explained John Ashworth, managing director of Tramex Ltd. “The better meter manufacturers provide meters that can carry out both non-invasive testing and relative humidity testing to obtain the best information.”

James Keene, president and owner of Keene Building Products, said there is one mistake to avoid at all costs: Not doing any moisture testing at all. “Often you’ll see that a floor finisher is scheduled on a project 10 days after the floor is poured, and to keep the schedule the project proceeds without testing. The lack of a moisture test is a major mistake.”


Know your materials

When installing a flooring product, be aware of the limitations, noted Mihir Gandhi, W.F. Taylor’s creative design manager. “Know the maximum amount of allowable moisture for both the product being installed and the adhesives being used to install these floor products.”

Arthur Minite, LATICRETE director of technical services, echoed those sentiments. “Have a total understanding of the project from the get-go. Complete knowledge of what materials will be used within the installation assembly and what special instructions are prescribed prior to application are key elements to a successful installation.”

However, sometimes certain types of flooring should be abandoned if the conditions cannot be met. “Some jobsites are simply not suited for certain types of flooring installation, regardless of how much [moisture] protection is employed,” said John Lio, DriTac marketing manager.

For example, a crucial step when installing wood flooring is to give the wood enough time to acclimate. According to Paul Laurenzi, Delmhorst Instrument Co. vp sales and marketing, flooring strips or planks should always be brought to equilibrium before installation. “Often contractors do not allow the floor to acclimate to the subfloor, potentially resulting in costly repairs later on.”

To identify wet areas in wood floors, pinless meters can be used. A pin-type meter, on the other hand, is best for finding the exact location of the moisture in a wood subfloor.

“If a problem occurs after installation, the key to finding hidden moisture is to use an electrode with insulated contact pins. These pins read only at their uninsulated pin tips, allowing the contractor to drive the pins into the floor and through to the subfloor, noting readings at each level of penetration,” Laurenzi said.

A hygrometer is recommended to measure humidity on the job site, added Duane Reimer, MP Global Products technical director. It is generally recommended for humidity levels to stay between 35 and 50 to 55 percent, but the most important consideration is to adhere to a manufacturer’s instructions. “Most hardwood floor manufacturers will not uphold a warranty claim if the floors are not maintained within the company’s recommended humidity levels,” Reimer said.

Grete Heimerdinger, Lignomat USA vp, said that obtaining accurate moisture readings also requires taking the wood species into account. “Therefore, when a meter is used for every series of readings, the settings on the meter need to be recorded. If the material is not wood, the meter can still be used to take comparative readings, but the settings should be noted.”

She said if certain conditions are not met, a wood floor should never be installed. “Do not install over wet floor planks or wet concrete, and do not use wet subfloors. Before an installation can process, the problem needs to be found and eliminated.”


Tackling a moisture emergency

Waterproof membranes are designed to prevent the penetration of water into the substrate, and are available as sheet- or liquid-applied products. Sheet-applied membranes provide consistency but are not designed for anything other than flat surfaces. Liquid-applied membranes can be applied over flat or irregular surfaces, but require the mixing of one or more components and application with trowels, rollers or sprayers. The key is to choose the best product for the installation, Hightower said.

If the MVER levels are too high, it is time to look into a moisture reduction barrier. Polymer-based barriers can bring an MVER of 8 pounds or less down to acceptable levels, but can typically only be used on a slab that is green or less than one year old. Water-based and 100 percent epoxy barriers are designed to handle greater MVER levels, with 100 percent epoxy topics typically recommended for an MVER of 8 pounds or more, Hightower noted. Using a moisture reduction barrier will require the proper preparation and acclimation of the concrete to prevent out-gassing.

Another option is time. “If they have the time, most people will say that a consistent, higher-than-usual ambient temperature and low relative humidity, additional air movement across the concrete slab, and dehumidification equipment in the building will ultimately dry the slab to acceptable levels,” said Jason Spangler, Wagner Meters product sales manager.

Chris Ranwell, GE Sensing global product manager, agreed. “Moisture can be mitigated in buildings with time and the appropriate ventilation.”

But if all else fails, the most important step an installer or contractor can take is to immediately talk to the client. “An installer should first make his client aware of the issues and try to determine what is causing the high moisture levels – i.e., plumbing or drainage issues or problems with a new slab – and then try to remedy these issues,” said Mark Lamanno, Franklin International technical market manager.

Bruce Newbrough, ARDEX Americas director of application development and product advancement, recommends calling a meeting with the general contractor, the architect, the owner or a representative, as well as manufacturer representatives of the flooring, adhesive, underlayment and remediation systems.

“Get everyone together and explain the test results and what the ramifications of installing without correcting the problem are. If the moisture testing shows results that are too high for the flooring system to be installed, a failure will occur a few months down the road and will disrupt the business tremendously. Address it now. The costs will be much lower in the long run.” 


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