High moisture content in a concrete slab can wreak havoc on any type of flooring system, whether it’s epoxy, carpet, wood, vinyl, stone, or tile, and can affect concrete of any age or location.
According to the ASTM standard, concrete slab RH levels should not exceed 75% when flooring is installed unless otherwise allowed by the flooring manufacturer. Flooring problems that can occur due to excessive vapor transmission include delamination, adhesive failure, cracking, bubbling, or peeling of epoxy floors, discoloration, slippery or uneven surfaces, reduced flooring material lifespan, deterioration of the concrete slab, and growth of mold and other pathogens.
There are a number of reasons why concrete may contain too much moisture. First, the concrete must be properly cured and dried, which can often depend on the water-to-cement ratio. After a slab has cured, water migrates upward through capillaries in the concrete and escapes into the air. Moisture can also be the result of poor drainage or improper vapor barrier below the slab-on-grade, plumbing problems, rainfall, and high humidity in the air. A dry appearance is a poor indicator of moisture in a concrete slab as moisture levels can vary significantly at different depths. The general rule of thumb for how long it takes concrete to dry is 30 days per inch of depth, but this should only serve as a guideline; concrete slabs should always be properly tested prior to flooring installation to ensure that moisture levels meet ASTM standards and manufacturer specifications.
There are a number of concrete slab moisture testing methods, with the gold standard being ASTM F2170 relative humidity testing, which measures RH at various depths using a special meter and in-situ probes. Another highly-reliable test is ASTM F1869 calcium chloride test, which measures emitted moisture by comparing the weight of a container of calcium chloride placed on the slab at the start of the test with its weight 60-72 hours later. The simplest and most economical concrete moisture test is ASTM D4263, in which a plastic sheet is taped to the concrete and checked for accumulation of condensation under the plastic after 18-24. Unlike ASTM F2170 and F1869, which can accurately measure moisture in a concrete slab at a point in time, D2463 can only be used as an indicator for the presence of moisture.
SRI & Company is expert in an array of flooring design and installation services including concrete moisture mitigation and concrete slab moisture testing. For more information, please contact us at (973) 832-7627.
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