Thursday's #MAPEITechTip: What is MVER in a concrete slab? And how do you QUANTIFY MVER?

What is MVER in a concrete slab? MVER is the Moisture Vapor Emission Rate, or the amount of moisture vapor that under the right conditions (differential of temperature & pressure within the slab) rises up through the capillaries of the concrete, with the potential of the water vapor condensing back into a liquid under the floor covering. For example, if you have a concrete slab with a MVER of 25lbs. per 1,000sq.ft. per 24 hours, this emission rate would produce approximately 21 U.S. gallons of water every 7 days. Now imagine this vapor drive under thousands of square feet of moisture sensitive resilient flooring—the potential for failure if this moisture is not addressed and managed can be catastrophic in downtime, additional costs and reputation.

How do you know if the MVER in your concrete slab is excessive? The key is to QUANTIFY the amount of moisture vapor within the slab this can be done using one of the ASTM test methods, such as the ASTM F1869 Calcium Chloride Test that quantifies the amount of moisture vapor emitted from the slab or the ASTM F2170 Relative Humidity Test which quantifies the percentage relative humidity (RH) within the concrete slab. Always consult the finished covering manufacturer for moisture limitations expressed in either lbs/sq.ft./24 hours or percentage of RH to ensure your tests do not exceed these limits prior to installing your floor covering.

Remember when Quantifying the MVER in a slab:
• Ambient RH and temperature can significantly affect test results
• Tests are a snapshot in time of moisture emission
• Only reflect upper portion of the concrete slab
• Can’t predict long term ‘floor system performance’—particularly if the ‘vapor retarder’ under the slab is non-existent and/or damaged

For additional information, consult the Guidelines in the most current editions of ACI 302 and ASTM F 710 “ Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring”