How to Test for Excessive Concrete Moisture – The Biggest Cause of Flooring Failures
by Arif Kalam - Director of Sales and Business Development
Concrete moisture is the biggest cause of flooring failures with all commercial projects. Interior concrete floors are subject to possible moisture vapor emission and excessive alkalinity, which can ultimately cause a coating system to fail. Such failures result in multi-millions of dollars in claims and materials replacement charges annually.
The good news: failures due to concrete moisture are preventable!
We recommend conducting the following ASTM-approved tests ahead of any installation. Each measures different aspects of concrete moisture, and they should be conducted together to accurately assess concrete moisture conditions.
Calcium Chloride Moisture Testing per ASTM 1869-04
The calcium chloride moisture test is designed to quantify the volume of water vapor emitting from a 1,000 sq. ft. concrete slab over a 24-hour period.
Here’s how it works:
- The building must be acclimatized to the anticipated service conditions for 48 hours prior to testing.
- The concrete should then be cleaned by light grinding.
- A dish of anhydrous calcium chloride should be pre-weighed and placed on the cleaned concrete. The dish is covered with a plastic dome and sealed to the floor, as illustrated below. After 60-72 hours, the dome is removed, the dish reweighed, and the weight gain is calculated.
Through a calculation, the weight gain is expressed in pounds of moisture emitted from 1,000 sq. ft. in a 24-hour period. Safe levels of moisture vary from 3-5 pounds depending on the flooring manufacturer’s recommendation. A low reading may only indicate that the upper portion of the concrete is dry enough to receive flooring, but moisture deeper within the slab has not been measured and may be at unacceptably high levels just waiting to rise to the top of the slab.
Once a low-permeability coating is installed, the total moisture within the slab redistributes itself to reach equilibrium and the upper portion of the concrete will become wetter. The number of pounds measured after low-permeability coating is installed will very likely be higher than the pre-installation measurement.
Relative Humidity (RH) Testing per ASTM 2170
Relative humidity is a measure of equilibrium moisture level. RH probes can determine the relative humidity of a concrete slab below the surface at various depths.
Here’s how it works:
- Holes are drilled into the concrete at specified depths, and fitted liners are inserted into the bottom of the hole.
- The liners are capped and allowed to equilibrate for 72 hours before inserting the probe.
- If this reading is taken at close-to-mid slab depth, it will be representative of the level of moisture that the flooring will be exposed to after the slab is covered and a new equilibrium reached. Acceptable levels of relative humidity within the slab range from 75-85% depending on the flooring installed.
Since the probe testing is conducted on the interior of the concrete, it’s much less susceptible to atmospheric conditions above the slab that can skew the results of a calcium chloride test. For this reason, it’s more useful in determining moisture levels in non-acclimatized areas.
Interior commercial projects of all types and sizes should start with both concrete moisture tests. Putting in the extra effort at the start of the project can save major time, hassle and money down the road.
We also encourage you to visit our VaporSolve™ Moisture Remediation Systems, which are highly specialized epoxy coating systems formulated to isolate all levels of concrete moisture.
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