Measuring Relative Humidity in Concrete per ASTM F2170

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Currently, the relative humidity (%RH) reading that you get can in concrete slabs vary depending on the manufacturer of the instrument that you use. The reason for this seems to be the vertical location of the RH sensor in relation to the bottom of the drilled hole. Everyone seems to agree that holes should be drilled to 40% of the thickness of a slab. That’s the location that best approximates the RH of the entire slab thickness. Sensors placed close to the bottom of the hole will read higher than sensors located higher up—results with current instruments can vary by as much as 8 to 10% RH due to sensor location and other factors of probe shape and internal construction. Members of ASTM committee F-6, which is responsible for F2170, are attempting to agree on probe and sensor geometry so that everyone’s instruments report more similar results. Until there is consensus on this issue you are left to decide which instrument reports the most useful RH. Generally, higher readings are a more accurate indicator of the moisture condition at the bottom of the hole.

Every manufacturer of finished floor products publishes maximum acceptable concrete %RH for their product installations. Some companies specify RH numbers that aren’t attainable for concrete to ever achieve, leading to situations that contractors can’t meet. Often times this leads to contractors voiding manufacturer warranties in order to install products on a timetable required by project owners.

Tell us about your experiences. Do you measure the %RH of your floor slabs? What has been your experience with installing finished floor products?


Comments (3 Total)

  • Posted by: DonC | Time: 8:33 PM Monday, July 18, 2011

    The current Standards in Australia for Carpet & carpet tiles (AS 2455.1:2007) calls for surface testing with a hygrometer and pH testing. The resilient flooring standard (AS 1884-1985)calls for the same plus an electrical resistance meter can be used. Our experiences over the last few years have shown us that both the surface testing and electrical resistance meter testing are unreliable due to many issues including curing compounds in the concrete, poor testing practices and highly burnished surfaces which affects the surface testing (the current Australian standards do not state that the burnished surface of the concrete should be taken off prior to testing so builders will not allow you to do this as they state that it is not complying with the standard). We are currently on a large amount of complaints where the floors have been moisture tested with either of the 2 moisture test methods noted above (no pH testing was done) and after 6-12 months the floorcoverings have blown off the floor and in some cases the floorcoverings are off-gassing due to the adhesives reacting with the high pH and PVC backings. We currently only use insitui RH probes in conjunction with pH testing and have found these to be very reliable. Both Australian Standards are currently under revision and the insitui probes are being included in both standards. The amount of holes noted in ASTM F2170 is under question here with the Australian Standards and also the 72 hour period is being questioned as builders here do not want to wait the 3 days for a result. Also in new buildings the HVAC systems are never running when moisture testing or the installation of the floorcoverings are done. We use the Wagner Rapid RH and find that we get results within an hour that read within 3-5% every time of the results we get after 72 hours.

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  • Posted by: Joe Nasvik | Time: 5:19 PM Friday, April 08, 2011

    Thanks for your comment. The difference between the calcium chloride test and the relative humidity test is the difference between measuring the surface area of a body of water and including the depth to determine what the volume of water is. The calcium chloride test looks at the surface area to estimate the rate of evaporation while the RH test provides information about how much water there is. Many people think the calcium chloride provides enough information to make the decision about whether to proceed with surface finishes. But others think that RH numbers are a better predictor of successful installations over time.

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  • Posted by: eaadams | Time: 12:44 AM Tuesday, March 29, 2011

    We do and prefer rH testing. However, frequently architectural specs call for CaCl testing and GC's will often object to high rH numbers that are not in original specs. Most testing firms in California (geo tech etc...) do CaCl testing wrong. Frequently I will see PE's lay a CaCl kit by showing up, wiping off the slab, and running the test. No proper site prep. No three visits. Just two. This is wrong. I've just completed a project where the state officials (Cal DSA) approved this sort of testing. You don't object to DSA because they can and will cut your knees off if they choose to put a magnifying glass on you. So you have to say ok and keep working. I saw a project bid last week where the architect said the slab tested at 1.5#. It is a VAT floor so old it probably has no vapor membrane but because an uninformed engineer working for the state did a bad test regime the floor was bid with no major remediation. Also, flooring competitors will use CaCl testing because they can get artificially low tests to get material in by manipulating the test by doing it wrong. Finally, I have seen a disturbing trend by our largest competitor where they essentially engage in a bait and switch. They will spec a project knowing it will test high, bid the project low (~$6 s/f), wait for project to be built, go test the floor, and then hit owner with a $4-$6 change order as they begin to install which is usually right before turnover since it is floor covering. So, the owner doesn't have any time to adjust their plan and because the contractor has a contract they can't break it off and go with another company with a higher moisture product. I think the largest problem is the poor adoption of these ASTM/ACI standards. ASTM F1869 has been adopted but never properly placed in specs. ASTM F2170 remains under spec'd. ACI 302.2R06 is only referenced in product specs never in slab or cast in place specs. If ASTM and ACI would spend more time getting their standards into specs they would be more effective. Lastly, the constant changes doesn't help. ASTM ACI specs seem to change ever year or two. The industry hasn't really adopted the standard and ASTM / ACI changes the spec.

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About the Blogger

Joe Nasvik

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Joe Nasvik has been senior editor for Concrete Construction (CC) magazine since March 2000, where he writes articles about all segments of the concrete industry and specializes in decorative concrete construction. Nasvik is a member of the American Concrete Institute (ACI) and the American Society of Concrete Contractors, on the board of the Decorative Concrete Council, and represents CC in the Concrete Foundation Association. On the ACI national level, Nasvik is a member of the Construction Liaison Committee, the Aesthetics Committee 124, Decorative Concrete 310, and Decorative Concrete Finisher C601-D. He attends meetings of the 302 Floor Construction committee, 343 Bridge Design committee, 130 Sustainability committee, 117 Tolerances committee, and 363 High-Strength concrete committee.

Considered a leading authority on concrete, Nasvik was a professor in the Applied Behavioral Science Department at a small college until 1974 when he started Chicagoland Concrete Specialists (CCS)—a concrete construction company in the Chicago area. As a Bomanite contractor, his company installed all forms of special pavement. As one of the early stamped concrete contractors, he worked out mix designs for freeze/thaw climate use and performed durability tests in lab testing facilities. CCS also constructed high-strength warehouse floors, installed other general concrete flatwork, and specialized in the installation and waterproofing of landscape features and waterfalls using rock textured panels made with glass fiber reinforced concrete and masonry unit formlined concrete wall construction. Nasvik holds a master's degree in Group Dynamics and a master's degree in Social Work.