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Concrete Moisture Vapor

The only method of determining water vapor emission escape from concrete is by using an anhydrous calcium chloride test (ASTM F1869) method.  This test method absorbs water vapor emission escaping from the concrete surface under a controlled dome using a pre-weight amount of anhydrous calcium chloride.  The test is calculated based on a weight gain vs. the number of hours of exposure to the concrete surface.  The end result is expressed in lbs. per 1,000 square feet in 24 hour period. 

The test method differs from concrete moisture content and in-concrete relative humidity testing devices due to its unique absorption of concrete moisture vapor escaping from the surface.  To properly perform this test method a 20 inch x 20 inch area needs to be cleaned of curing, sealing and substances that will block the release of water vapor emission.  As with all concrete test methods, an ideal test is performed during conditions that are representative to the final conditions of the building.  Testing during uncontrolled temperature-humidity conditions will offer results for that time period and must be considered invalid. 

The tests are installed based on the amount of floor products to be installed at a rate of three (3) tests for the first 1,000 square feet and one (1) additional test for each 1,000 square feet thereafter.  Testing at this rate is used to capture the various concrete pours used during the buildings construction and verifying tests at many locations to determine the concretes dryness for flooring.  A common sampling is 13 tests for projects with 10,000 square feet of flooring.

Testing equipment is installed for a period of 60 to 72 hours and remains undisturbed during the absorption of water vapor emission.  During this time period the concrete emission escapes over various interior conditioning (night vs day temperature-humidity changes) is later calculated into a 24 hour period.  The test results are commonly expressed as lbs. of emission per 1,000 in 24 hours.  A typically mistake is to perform the test for 24 hours rather than the 60 to 72 hour period.

A rate of 3 lbs. per 1,000 square feet in 24 hours of emission has been established as the industries lowest vapor emission rate for floor products, adhesives, primers, cement patching products and specialty floors.  However each manufacturer has a different marketing position on how much water vapor transmission there flooring will tolerate.

The higher the moisture vapor emission rate the greater the risk for dampness (condensation) to occur under the flooring system after product installation.  The increased dampness causes the concrete’s natural alkaline levels to reach surface and this new elevated alkalinity-pH concentration to destructively attack-damage the flooring systems properties.  See alkalinity-pH introduction for additional details.

List Check:

1) Clean the concrete surface of curing compounds, sealers and adhesives.

2) Perform the amount of tests required by ASTM F 1869.

3) Verify the HVAC is operational.  If the system is not balanced and operational, than low results are for the current conditions only!

4) Allow the test to be exposed to the concrete surface for a period of 60 to 72 hours.

5) Verify alkalinity-pH results at each test location.