Question: I am employed by a home builder and currently dealing with a homeowner who is claiming moisture damage to the hardwood flooring in her home. She hired a professional who completed the ASTM F2170 test and came up with the following results:

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All these tests were taken from the first floor slab two years ago in July. I am unfamiliar with F2170 testing.

Answer: The ASTM F2170 test, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes, was approved in 2002. It covers using a relatively new (to the United States) technology that checks the moisture content in the heart of the slab rather than at the surface and provides more meaningful information than the traditional calcium chloride test, which is covered by ASTM F1689. Both test procedures are available for purchase on the ASTM Web site, www.astm.org.

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The RapidRH combines a sensor, power supply, and display for testing the relative humidity of a slab from the inside.

Credit: Wagner Electronics

The F2170 in situ procedure requires testing the floor at three points. A small hole is drilled at each point and an electrical instrument is inserted to measure the relative humidity near the midpoint of the slab. The instruments generally fit into the holes like small corks. Some can be read directly, but others connect to another device that records the data.

The F1689 calcium chloride test has been used for many years but only measures the rate of moisture vapor transmission, in pounds per thousand square feet over 24 hours. The problem is that when it comes to moisture, concrete slabs behave like sponges. The moisture vapor transmission rate—how much is being given off at any given time—depends on the ambient conditions above the slab. Moisture moves toward drier areas, so if the air conditioning system is drying the air in an enclosed space above a concrete slab, it also is drawing moisture out of that slab. In a worst case scenario, where there's a source of water below the slab and no vapor barrier, the slab can act as a conduit for bringing moisture into the space.

Now to get back to your primary question: flooring manufacturers provide guidelines for determining if conditions are right for installing their products. As far as moisture in concrete slabs is concerned, guidelines vary depending on the type of material and how sensitive it is to moisture vapor, how well or poorly moisture vapor passes through it, and the possible effects on adhesives. To deal with your situation, you should obtain the installation guidelines from whoever provided the hardwood flooring and see how they compare to the test results. However, that may be more difficult than it first would appear. Although many flooring manufacturers have incorporated guidelines based on the new relative humidity measurements from in situ testing, some still only give limits based on moisture vapor transmission tests.