Moisture Vapor Emission Tests

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Author Message Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 121 Registered: 05-2005 Posted on Wednesday, January 03, 2007 - 03:33 am:    The American Society of Concrete Contractors came out with an interesting position statement which they published in the March 2005 edition of Concrete International (think ACI). They say: 1) Emission tests can't determing concrete quality. For example a slab with a water cement ratio as low as 0.4 can emit moisture at the same rate as concrete with a w/c of 0.7. 2) Emission tests cannot measure concrete permeability. The tests do not measure the steady state flow of the water through the concrete and thus cannot measure the permeability of the slab. 3) Emission tests only measure the conditions at or near the concrete surface. Thus installing a vapor barrier under the slab will have little or no impact on the emission test results. If they are right, and based on other sources I do believe they are, then this suggests that much of the rational for performing emission tests is wrong. Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 185 Registered: 10-2003 Posted on Wednesday, January 03, 2007 - 11:04 am:    I have had numerous arguments/disagreements over moisture vapor emissions and the use of vapor "retarders" not "barriers" under slabs-on-grade. Here is my 2 cents: 1. Emissions tests are not designed to determine concrete quality, there are other tests for that. I don't agree with the 2nd part of the statement either. W/C ratio determines amount of water in slab - the higher the W/C ratio, the more bleed water. I don't see how the moisture rate can be the same. 2. True - Maybe we should ask for permeability tests? 3. While maybe having little impact on emmissions tests, Vapor Retarders are still need to limit the amount of ground water permeating through slab. Use of a vapor retarder also limits the amount of vapor emissions to the bleed water in the concrete. Remember - this is a contractor's association talking, looking for a way to get out of their responsibility to: a. Produce quality concrete with low moisture vapor emissions. b. Install vapor retarders. While at the same time, trying to pass the cost of mitigation of high moisture vapor emissions onto the Owner or Architect. George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 244 Registered: 11-2004 Posted on Wednesday, January 03, 2007 - 11:39 am:    Question: "Emission tests" = ASTM F 1869, the calcium chloride test? If so, I am used to seeing these tests used to evaluate "how wet the slab is" prior to installation of finish flooring. And I understand that the probe test (F 2170?) is now becoming preferred for this use because it measures the moisture within the slab. Both of these consider the slab as a substrate for a finish, more of an architectural issue than structural. Are there other vapor emission tests used that relate to this discussion besides the calcium chloride test and the probe test? (...ignoring the old duct tape a piece of poly to the slab overnight, which is pass/fail at best) Mark Gilligan SE, CSI Senior Member Username: markgilligan Post Number: 122 Registered: 05-2005 Posted on Wednesday, January 03, 2007 - 12:07 pm:    As for the argument that the Contractor is just trying to get out of their obligation similar conclusions have been reached by other parties. Their conclusions are supported by a tests. The emission tests only measure the moisture in the top layer of concrete and thus are not a valid measure of the long term conditions. The permeability of normal concrete would allow less moisture to flow to the floor covering than implied by the manufacturers test criteria. The emission test results can vary significantly depending on the fineness of the calcium crystals. If you want to bias your results find out how course the crystals are. Until these emission tests are determined to be junk science we still need to follow the manufacturers recommendations if for no other reason than to give ourself and our client protective coloration in case their are flooring problems. In the mean time we should look at the growing body of test results and try to understand what is the real problem. If the tests being used are questionable then can we really understand the cause of problems when they do occur. Dale Roberts CSI, CDT Senior Member Username: dale_roberts_csi Post Number: 16 Registered: 10-2005 Posted on Wednesday, January 03, 2007 - 01:33 pm:    The TCNA (Tile Council of North America) and most of the manufactures of adhesives and Thin-sets recognize and use the Calcium Chloride method of testing concrete slabs to determine the dryness of the concrete slab (ASTM 1869). The Calcium Chloride test typically only measures the top ˝” of the slab. A newer test ASTM F-2170 measures relative humidity levels within the concrete slab, sometimes referred to as RH (relative Humidity). Testing should take place in a building that has the same temperature and humidity levels as the tenant will require in using the space, otherwise it may leas to false test results. For Organic adhesives pH levels also become important. Proactive testing, even though it has its limitations is still the best way we have to test the slab before installing any floor covering. I always recommend a vapor retarder directly underneath the slab and the blotter layer under the vapor retarder. The blotter layer will hold moisture and allow vapor transmission thru the slab. In a 1965 study “moisture Migration – Concrete Slab on Ground Construction” H.W. Brewer tracked moisture outflow of concrete as it dried. His study shows that high water / cement ratio concrete takes longer to achieve low level outflow than drier mix designs. This study alone justifies specifying concrete with a maximum water / cement ratio between .45 and .50 on all projects that require floor covering installation at slab ages of 6 months or less. Nathan Woods, CCCA, LEED AP Senior Member Username: nwoods Post Number: 147 Registered: 08-2005 Posted on Wednesday, January 03, 2007 - 01:56 pm:    The TCNA may still recognize the dome test (Calcium Cloride method), but it HAS been depreciated in it's value in recent years. On another thread similar to this one, I posted: ---------------------- "In recent years, the dome tests have been disregarded as inappropriate in common applications. Please refer to the site listed earlier in this thread for the following articles: - http://www.kenbondy.com/images/ProfessionalArticles/MoistureDomeTests1.pdf - http://www.kenbondy.com/images/ProfessionalArticles/VETTalkCGEA.pdf The authors of this report are widely considered to be among the most sought after experts in the field of concrete and slab design. " ------------------------ Here is the origional thread: http://discus.4specs.com/discus/messages/23/2611.html Dale Roberts CSI, CDT Senior Member Username: dale_roberts_csi Post Number: 17 Registered: 10-2005 Posted on Wednesday, January 03, 2007 - 02:32 pm:    Yes I agree with you Nathan, the Calcium Chloride test is not the best test and does have its limitations. Pro – this test is accepted by most manufactures of floor covering, adhesive products for concrete dryness and suitability for the installation of their products and the test is easy and inexpensive. That is a big plus for most flooring contractors. Con – The Building should be acclimated at the temperature levels during occupancy use (which it never is). It only reflects the top ˝” of the slab. Home made calcium chloride test are easy to make and are delivering questionable results. Floor preparation is not done properly. The Relative Humidity test is a much better test. By the way, we have seen more moisture related problems in Arizona where they typically do not recommend vapor retarders under the slabs. Wayne Yancey Senior Member Username: wyancey Post Number: 251 Registered: 05-2005 Posted on Wednesday, January 03, 2007 - 07:18 pm:    There is a good article by H. Maynard Blumer for Arizona residents. "Specifying Shrinkage-Crack-Free Concrete: A Lesson from the Desert." The Contruction Specifier, December 1989, p.23. Also worthy of reading is Maynard's follow up article "New Justifcations for An Old Debate: Specifiying Vapor Barriers Under Slabs-on-Grade. "The Contruction Specifier, February 1990, p.27. Steven Bruneel, AIA, CSI-CDT, LEED-AP Junior Member Username: redseca2 Post Number: 2 Registered: 12-2006 Posted on Monday, January 08, 2007 - 07:50 pm:    Finish floor products that are applied with some sort of adhesive that when installed create a relatively impermeable finish can fail if there is too much moisture in the concrete assembly. Many flooring products available now have incredibly little permeability. Combine that with VOC requirements that restrict installation to not the best adhesive but the one that passes the VOC limit, and you can have problems. It is important to cover the moisture requirements for the each specified flooring to maintain flooring guarantees and warranties. Most flooring manufacturers specify a slab mositure emmission of no more than 3 to 5 pounds per the calcium chloride test. This is NOT limited to slab on grade (per the comment in the first post) but includes elevated interior concrete filled metal deck assemblies or cast-in-place interior raised decks. The membrane placed underneath a slab on grade is there to stop the transmission of "new" moisture, but there can be enough moisture present in a fully cured upper deck to cause a flooring failure. Architectural specifications should include a slab moisture control solution in DIVISION 7.