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common problems with cacl testing

As a special inspector for an engineering firm here are some problems that my lab has had for using cacl test are as followes.
-The subject building must be acclimated at or near the temperature and relative humidity levels anticipated during occupancy or use. This is often a difficult requirement to meet on a new construction project. If the HVAC system is not operational at the time of testing a recording hygrometer should be employed to monitor and record ambient temperature and relative humidity levels for comparison to intended occupancy conditions. Significant variance between the test environment and intended use environment should cause test data to be questioned.
- 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 1/4 to 1/2 inch of the slab's thickness.
- If ambient environmental conditions immediately preceding testing has 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.
-Tests are being set without floor preparation as required by ASTM F-1869. 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 is our experience that some of these products will slowly degrade leading to latent moisture release from the concrete and eventual floor covering system failure.

You are absolutely correct. the cacl2 testing only measurers the top surface. unless the slab is close to being in equalibrium the cacl2 test is going to be skewed. This is why a lot of the flooring manufacturers are going to the hygrometer probe testing. The F-2170 measurment at 40% the slab thickness is the apex of the drying curve. This is where the equilium line crosses the drying curve.

40% if the slab is drying in one direction only. 20% if it can dry from two directions.

I just had a client call and ask how in the world can they probe a 12" thick slab? I asked if it was cast-in-place and they confirmed it was, so they only needed to go 2.4" into the concrete, or 20%.

I know you guys know this, but sometimes these threads get Googled up, and someone may mistake 40% as a constant. Big Grin
JD Grafton
Concrete Answers for Flooring Problems

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