BELL FLOORING SCIENCES GROUP

DIV OF BELL BUILDING SCIENCES GROUP

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TESTING FOR CONCRETE MOISTURE & ALKALINITY

About Concrete Moisture and Alkalinity | Testing for Concrete Moisture and Alkalinity

Concrete moisture and surface alkalinity testing are essential in the determination of the suitability of a concrete slab to receive a moisture-sensitive floor covering or coating. These tests should be performed on all concrete slabs regardless of their age or grade level.

Most U.S. producers of floor coverings, adhesives, and resinous coatings specify testing for the Moisture Vapor Emission Rate (MVER) of a concrete floor slab and/or the Equilibrium Relative Humidity (ERH) in concrete floor slabs to determine level of dryness and suitability for the installation of their products. ASTM International has written industry standards for testing the moisture of a concrete slab.

ASTM F1869-04 Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.

ASTM F2170-02 Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In-Situ Probes.

ASTM F2420-05 Standard Test Method for Determining Relative Humidity on the Surface of Concrete Floor Slabs Using Relative Humidity Probe Measurement and Insulated Hood.

ASTM F710-08 Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring offers recommendations regarding the suitability of a concrete slab for the installation of resilient floor coverings based on results achieved by these test methods. This standard states that moisture vapor emission, per ASTM F1869, should not exceed 3 pounds per 1,000 square feet per 24 hours, unless otherwise specified by the flooring or adhesive manufacturer. The standard continues by stating that relative humidity inside of a concrete slab should not exceed 75%, per ASTM F2170, unless otherwise specified by the flooring or adhesive manufacturer.

Moisture:

Moisture within slabs is prone to movement when temperature and humidity change, so testing for both relative humidity and moisture vapor emission is strongly recommended. Our agency can perform tests by both of these methods but it should be noted that any testing method has limitations and can NOT offer a guarantee of a long-term successful floor covering installation. No test can reveal everything that should be considered when making a decision about the installation of a floor covering or coating. Test results can only indicate a snapshot of the slab condition of a particular spot at the time of testing. Moisture vapor emissions are subject to seasonal fluctuations and any subsequent damages are beyond the control of the testing agency and the installation contractor. Changes in the interior environment, concrete slab, and subslab environments subsequent to testing may cause conditions to change and lead to flooring failures.

Before discussing the individual test methods, it is important to note that in our opinion, all existing test methods are capable of being "fooled" under certain conditions. An example, when a very porous concrete, or a concrete mix design with a high water/cement ratio, is placed without the protection of an effective sub-slab vapor retarder or barrier, concrete moisture content and vapor emission can vary dramatically with seasons or other changing conditions. There have been studies published that show an effect of installing floor coverings or coatings with limited permeability is that of increasing moisture content in concrete, when a sub-slab moisture source is available.

A typical example is when a warehouse area is converted to office space. Moisture Vapor Emissions Rate (MVER) testing results prior to the flooring installation meet the specifications required by the floor covering or coating manufacturer so a new floor is installed. Soon after installation, the flooring or its adhesive system fails and subsequent tests are performed. The new tests reveal MVER levels far higher than the original test results and the inevitable finger pointing ensues. The concrete surface in the open warehouse had in fact dried sufficiently to reveal MVER levels low enough to pass the requirements of a flooring manufacturer. After the concrete subfloor is covered, moisture content in the concrete may begin to rise and can cause a failure of the floor system. The in-situ relative humidity test can, in many instances, detect this problem as it is reading within the slab.

This problem can also be seen when broadloom carpet is replaced with sheet goods or wood products or with the installation of a coatings. There should always be concern when covering or coating concrete that is not protected by an effective sub-slab vapor retarder. Many flooring manufacturers specifically require the existence of a sub-slab vapor retarder beneath slab-on-grade concrete when their materials are to be installed or the installation of a topical moisture remediation system.

Moisture Vapor Emission Rate (MVER):

The Anhydrous Calcium Chloride (CaCl2) Moisture Vapor Emission Test was developed to quantify the amount of moisture vapor emission from a concrete slab. ASTM F1869-04 is the most current edition of this testing protocol. This test measures the amount of moisture absorbed by the calcium chloride, over a known area of concrete (dome area), over a known period of time (60-72 hours).

The test is performed by placing a quantity of calcium chloride in an open dish and placing the dish on a clean, abraded concrete surface. The dish is covered by a dome of approximately 9" x 9" and 2" in height. This dome is sealed to the concrete to isolate the test area. The test apparatus is left undisturbed for a period of from 60 to 72 hours. At the end of the test period, the dish is retrieved and any weight gain of the dish is attributed to moisture leaving the concrete and being absorbed by the calcium chloride. A mathematical formula converts this data to a result providing the number of pounds of moisture vapor emissions per 1000 square feet per 24 hour period.

Although results of calcium chloride testing are accepted by most U.S. manufacturers of floor covering, adhesive and resinous coating products as a benchmark for concrete dryness and suitability for the installation of their products, it is becoming a less preferred test method. As noted above ASTM F710 contains the statement that concrete can be considered suitably dry when the moisture vapor emission rate does not exceed 3 lbs. of water per 1,000 sq. ft. per 24 hours, when tested in accordance with test method ASTM F1869. The testing density required is a minimum of 3 tests for the first 1,000 sq. ft. with one additional test for each additional 1,000 sq. ft. of concrete slab surface or fraction thereof.

The subject building must be acclimated at or near the ambient temperature and relative humidity levels anticipated during occupancy or use. This is often a difficult requirement to meet on a new construction project. If these conditions cannot be met, the ASTM standard offers tolerances which, at a minimum, should be honored if accurate test results are anticipated. If the HVAC system is not operational at the time of testing a recording hygrometer should be used to monitor and record ambient temperature and relative humidity levels for comparison to intended occupancy conditions. Significant variance between the environmental conditions prior to and during testing vs. the environment conditions of the intended use can result in unreliable or erroneous test data. As discussed in the About Moisture section, the vapor pressure differential, created by temperature and humidity have a direct controlling influence on moisture vapor movement.

Some issues with the Calcium Chloride test

• Snapshot, no trend, short term response

• Susceptible to temperature and relative humidity (RH)

  • Higher ambient temperature and relative humidity = higher apparent MVER

  • Lower ambient temperature and relative humidity = lower apparent MVER

  • Higher floor temperature = higher MVER

  • Lower floor temperature = lower MVER

• Affected by the water/cement ratio

• Measures only top 3/4" depth of slab

• Cannot distinguish lightweight aggregate moisture reservoir

• Underestimates high MVER levels and overestimates low MVER levels

• Cannot distinguish between presence or absence of a vapor retarder

Calcium chloride tests reflect moisture vapor emission from the surface of the concrete. It has been suggested that the test reflects moisture in the top 3/4 inch of the slab's thickness with 90% of the measured MVER coming from the top 1/2 inch of the slab. If ambient environmental conditions immediately preceding testing have been extremely dry or wet, the concrete surface may be affected and test results may be skewed accordingly.

Testing on an open or breathing concrete surface may not reflect moisture deep within or directly below the concrete slab. Once covered by a low permeability floor covering or coating, concrete moisture content will equalize within the thickness of the slab. This may result in a higher moisture level in contact with the floor covering or coating at the surface of the concrete slab after installation than what was originally anticipated.

Surface contaminants and residue from paint, adhesive, curing or parting compounds can reduce vapor emission at the test site and produce inaccurate test results. Some penetrating parting compounds (tilt-up construction) or penetrating cure and seal products are difficult to detect and impossible to remove. They restrict moisture release and result in reduced vapor emission test results. It has been found that some of these products will slowly degrade leading to latent moisture release from the concrete and eventual floor covering or coating system failure.

Concrete Relative Humidity Testing:

Relative Humidity (RH) testing of concrete slabs has been used extensively in Australia, New Zealand, Scandinavia, and the United Kingdom. There are two types of concrete RH test methods, internal slab (in-situ) RH and surface RH.

The American Heritage® Science Dictionary defines relative humidity as "The ratio of the actual amount of water vapor present in a volume of air at a given temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage. Warm air can hold more water vapor than cool air, so a particular amount of water vapor will yield a lower relative humidity in warm air than it does in cool air." (Copyright © 2002 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.)

Dictionary.com Unabridged (v 1.1) defines relative humidity –noun the amount of water vapor in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature; the ratio of the actual water vapor pressure to the saturation vapor pressure. Abbreviation: RH, rh (Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006.)

In-situ Relative Humidity Testing:

The ASTM standard for in-situ RH testing is designated F2170-02 and follows similar procedures used in Europe. After side-by-side testing with calcium chloride kits, our firm believes that the In-Situ RH data is more useful and meaningful than calcium chloride test results although both test methods are recommended since they provide different data. 

It is our field experience that in-situ probes for the testing of slab-on-grade concrete offer results which are less impacted by ambient temperature and relative humidity conditions than the calcium chloride test. This generates meaningful data under conditions that may not be acceptable for calcium chloride testing. Concrete slabs in contact with the earth are a heat sink and their internal temperature is affected by both the sub-slab soil temperature and by the temperature of the air space above. Whereas the internal temperature of suspended concrete will be driven by the temperature of the air space above and below the slab.

It must be noted that ASTM F2170 states that slabs, which are to be tested should be "at service temperature and the occupied air space above the floor slab shall be at service temperature and service relative humidity for at least 48 hours before making relative humidity measurements in the concrete slab." Testing density required is a minimum of 3 tests for up to 1,000 square feet, with one additional test per each additional 1,000 square feet of concrete slab surface or fraction thereof.

This testing standard requires drilling holes to a depth based on a percentage of the slab's thickness. The hole is then lined with a plastic sleeve and a humidity sensor is installed or the sleeve is capped. The test site must be permitted to equalize for 72 hours prior to reading equilibrium relative humidity levels. After or during acclimation or equilibration, a probe is placed in the sleeve that permits readings to be obtained from the bottom of the hole, thereby offering a method to measure moisture content inside of the concrete slab reported as a relative humidity level.

Example of an in-situ probe

Testing performed at multiple depths permits a testing agency to develop a profile of moisture conditions through the thickness of a concrete slab. This information permits the user to make a more informed decision regarding the installation of floor coverings or the need to consider other alternatives.

It is critically important that probe temperature is at equilibration with concrete slab temperature. Testing should take place in an acclimated building and at the same density as noted above.

This test method is less subject to conditions occurring at the concrete surface that may influence calcium chloride test results. Test results appear to be less impacted by the type of, or lack of, floor coverings in place prior to testing.

Most resilient floor covering manufacturers recognize ASTM F710-03, which states in Section 5.2.2 "In accordance with Test Method ASTM F2170, the relative humidity in a concrete floor slab shall not exceed 75% at the time of testing, unless otherwise specified by the flooring or adhesive manufacturer." A listing of many of the manufactures who have adopted the ASTM F2170 test method in their specifications can be found here.

The flooring industry is seeing data developed by testing agencies that are not following the ASTM F2170 protocol, particularly with regard to equalizing of the test hole and/or test probe. Without temperature equilibration of the test site and testing apparatus, the data generated may be skewed high or low relative to the direction of inequity, thus rendering data collected misleading or meaningless.

Our testing agency uses instruments from various manufactures to perform testing in accordance to ASTM F2170 standards. This allows us to provide our clients with a diversity of technologies to perform testing. Our equipment includes testing instruments that allow us to provide not only snapshot readings but also automated data logging of the relative humidity and temperature trend recordings of the internal slab conditions and ambient environment.

Insulated Hood Relative Humidity Testing:

A newer testing method to the U.S. is the insulated hood relative humidity method which like the in-situ relative humidity method, has been previously used in Europe. The ASTM F2170 and F2420 both measure the equilibrium relative humidity and temperature. The hood method measures the equilibrium relative humidity and temperature directly above the surface of the concrete slab. Relative humidity readings from the hood method tend to be about five percent lower than those from the in-situ method.

The hood method measures the amount of free water in the air directly above the concrete surface and the calcium chloride method measures how much vapor is being emitted from the surface. One of the reasons humidity testing of concrete is becoming specified more often is that these methods are not as sensitive to atmospheric conditions as with the MVER method. 

The hood test method consists of securing an insulated air tight box to a bare concrete surface and the equilibrium relative humidity and temperature within the box is obtained through a probe which is inserted into the box. Like with the other moisture tests, the occupied air space above the test area shall be at service temperature and service relative humidity for at least 48 hours before making relative humidity measurements. This method is very good for those situations where drilling may not be advisable.

Alkalinity/pH Testing:

Testing for alkalinity is often overlooked but of extreme importance to a successful installation and like with moisture testing, it should be conducted on all floor regardless of the grade or age. pH is a measurement of hydrogen ion concentration that indicates the acidity or alkalinity (base) of a solution. ASTM F710 states that the surface of a concrete slab should be free of alkaline salts, and excessive carbonation or laitance prior to the flooring installation.

ASTM F710 also states that a concrete slab surface pH test reading shall be taken at the same frequency and at each location in which a moisture test is performed. A maximum pH reading of 9 is allowed unless the flooring or adhesive manufacturer states otherwise.

Our agency performs pH testing using both electronic pH meters and pH indicator paper.

Pre Test:

Prior to selecting test methods for any given project, it is recommended that the manufacturer(s) of floor coverings, coatings and adhesives selected for the project be contacted. In order to protect warranty rights, their specifications regarding acceptable test methods for determining suitability and dryness of a concrete slab should be followed.

Decision:

Too often a decision to install floor coverings or coatings is based on poor information or the simple demand to meet a schedule. If a concrete substrate has a moisture vapor emission level, in-situ relative humidity, or a pH level in excess of that which can be tolerated by the flooring material, the losses are rarely limited to the flooring itself. The tenant may end up, at best, with an eyesore, at worst there may be a trip or slip and fall hazard with dire financial consequences. The need to vacate a floor after move-in, while repairs are made, can be extremely costly and for many industries the loss of revenues can exceed the value of the floor by a vast magnitude.

It is the opinion of this agency that a combination of these tests, performed concurrently in a subject building, offers the greatest depth of data in decisions that may be made based on such data.

Please us our contact form or call us at 404-504-8900 if you would like to discuss commissioning our firm's consulting, testing, inspections, or other services.