The testing of moisture emissions is recommended for an owner, general contractor and flooring contractor to determine the level of moisture or the relative humidity in the concrete. Three commonly used tests are the PH test, Calcium chloride test and the Wagner RH test.
PH Test – The first test that should be performed is a simple PH test. High alkalinity levels are what you want to avoid. The high alkalinity levels can be an indication of too much moisture in a slab.
Calcium Chloride Tests – The most often used method of testing is to use Calcium Chloride Tests. This test uses Petri dishes filled with Calcium Chloride. The Petri dish is weighed before it is used.
The dish is put directly onto a patch of concrete that has been roughed up and cleaned of all contaminates. The dish is covered with a plastic dome and left to absorb the moisture vapors for a period of time no less than 60 hours and no more than 72 hours. The Petri dish is then reweighed and the amount of moisture vapor is calculated from a formula. This test measures the amount of moisture vapor emissions over time. Results of under 3 lbs of moisture emissions over a 24 hour time period for 1000 sf area is the benchmark. Some materials will allow you to go to 5 lbs of moisture emissions. Results like 10 or above indicate serious moisture emission issues. I have seen Petri dishes filled with water from an overabundance of moisture vapors.
Wagner RH Test - Another method to test for moisture emissions is a Wagner RH Test that measures for relative humidity levels inside the concrete. This test is recognizes as a more accurate testing method.
The test is performed by drilling a hole into a concrete slab and a RH gauge is inserted into the whole and left there. The advantages of this method are that the moisture levels are measured down in the slab instead of the top ¼ “ of the slab. This will give a more accurate assessment of the moisture levels present.
The additional reason for this test is that one can track the progress of moisture levels. For instance, lets say that the concrete slab is poured in Month 1. Six months later the owner installs his HVAC system and the HVAC system starts to draw the moisture in and under the slab out. If there is excess moisture in the slab, the use of a wagner rh test will allow you to monitor the improvement in the moisture levels over time. It has been my experience that it can take 3-4 weeks of continuous HVAC running to reduce a moisture reading to the acceptable 75% and below relative humidity levels that most manufacturers require.