[Concrete Flooring] Calcium Chloride Moisture Tests Vs. In Situ Tests

calcium chloride moisture test

If concrete has a natural enemy, there's no question that it's moisture.

Able to move through the durable, yet porous, material, moisture is capable of causing serious damage to concrete. From reducing its integrity to creating cracks, the longer concrete is exposed to excessive moisture, the worse damage becomes.

Whether a floor is meant to be exposed concrete (think: unfinished basement) or covered by another hard material (think: wood, laminate, or tile), understanding moisture presence in the slab is critical. Excessive moisture damage to concrete is costly to repair. The same goes for materials in direct contact with the concrete surface -- nothing doubles a wood floor's cost than having to replace it because of a moisture issue.

Like other materials, there's no one way to test for moisture in concrete slabs. The most common are calcium chloride testing and in situ testing.

Though both tests are still used to evaluate moisture in buildings, only one of these tests sets the standard and is considered the most reliable way to measure moisture presence in concrete.


Testing for Moisture in Concrete | Calcium Chloride Moisture Test Vs. In Situ

Checking moisture levels in concrete isn't as easy as it is for other materials.

Take drywall or wood, for instance. During a moisture survey, an inspector simply touches the prongs of a professional-grade pin-type meter to the material's surface and takes a reading in just a few seconds.

Because of concrete's composition, testing for moisture in a slab or floor isn't as simple. Rather concrete moisture tests are almost the polar opposite – even down to the devices used for testing.  

Whether you're conducting a calcium chloride moisture test or using the in situ method, both concrete moisture tests are more involved and take much more time. What's more, while both tests check for moisture, they provide two distinct measurements.

Let's take a look at both testing methods and their procedures:

What is Calcium Chloride Moisture Testing & How Does it Work?

A moisture measurement method dating back to the 1940s, calcium chloride tests are used to check moisture levels across a wide variety of building materials -- concrete included.

Calcium chloride moisture tests involve placing an anhydrous calcium chloride crystal (a salt) onto a predefined area of the material and measuring the amount of water released over a given period of time. Generally speaking, this moisture test takes three days to complete.

Because the crystal has a high affinity for water, it absorbs all sources of moisture it comes in contact with, including condensation, humidity, and even liquid. As more water is absorbed by the crystal, its size increases until it reaches its capacity limit.

Once the crystal has reached this equilibrium point, it's then weighed. The new weight is compared against the crystal's pre-test weight to calculate the moisture vapor emission rate (MVER). 

Calcium chloride moisture testing measurements are typically expressed as grams of water per kilogram (g/kg). A higher g/kg rating indicates more moisture in the material.

What is In Situ Testing & How Does it Work?

A newer moisture measuring method (comparatively speaking), in situ testing takes moisture investigations to a different level -- below the surface.

Considered the go-to method for evaluating moisture presence in concrete slabs, in situ testing measures actual moisture content from inside the material. Using specialized hygrometer probes placed in holes drilled into the slab (which are later sealed and left for 24 hours), in situ measures vapor passing through the material. In situ testing does allow for longer surveys, too. The testing can go on for days for days or months with probes left in place to continually monitor moisture. 

Readings collected are expressed in relative humidity (Rh). Like all other readings taken on a hygrometer, the higher the Rh, the higher moisture presence. 

Overall, this method provides an effective means of testing for moisture without needing to perform any major renovations or resurfacing work on existing concrete surfaces. In fact, the in situ method sets the standard (the ASTM F-2171) for in-place moisture testing and is the most reliable of all available test methods.

How to Check for Moisture in Concrete Floors With an In Situ Test

To test for moisture in a concrete slab using the in situ method, follow these steps (which are in accordance with ASTM F-2170):

  1. Drill three holes per 1,000 square feet in the area of a concrete slab being investigated to a depth equal to 40% of the slab’s thickness. 
  2. Clear the holes of dust and debris.
  3. Visually inspect the bottom of each hole to make sure you haven’t drilled into the heart of a piece of coarse aggregate (e.g. gravel).
  4. Set RH probe sleeves to the correct depth and insert them into each hole. 
  5. Insert RH probes into their respective sleeves and place a cap to seal each opening. 
  6. Wait 24 hours for the probes to equilibrate with their microenvironment’s relative humidity. 
  7. After one day’s time, take & record RH readings using a hygrometer.


However, these tests can become inaccurate if perfect conditions are not met. Temperature and humidity in the room greatly affects readings.  If not properly sealed to the concrete, the probe sleeves will let outside air into the microenvironment. Also, probes can be damaged at a job site.

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Why In Situ Tests Stand Above Calcium Chloride Tests

While both types of moisture tests do have their respective places for determining acceptable moisture levels in concrete floors, the in situ method is the preferred choice for checking levels within concrete floors or slabs.

Comparing both moisture measurement methods, in situ testing surpasses calcium chloride moisture tests with its:  

  1. Accuracy
  2. Efficiency
  3. Site disruption


1. Accuracy

In situ moisture testing is more accurate than calcium chloride testing due to its ability to measure Rh within the material itself.

In simpler terms, there's no better way to check a concrete slab's moisture than from the inside.

With measurements taken in a controlled setting, there's little worry about any potential errors caused by surface temperatures, coatings or vapor barriers, etc., which impact accuracy in calcium chloride tests. The same goes for other forms of moisture testing such as surface scanning and electrical impedance technologies for concrete surfaces.


2. Efficiency

This comparison is simple. Even with the prep work, in situ tests are faster to complete.

Performing a calcium chloride test takes upward of three days to complete, while the in situ method requires 24 hours to get accurate and reliable readings.

Another way to look at it: in situ tests take two-thirds less time than calcium chloride tests.


3. Site Disruption

Though in situ tests involve drilling holes in a concrete slab (something that would require repair later on), the test method is still less disruptive to a site.

Calcium chloride tests require that a surface is completely exposed before any testing can begin. This means having to rip up existing floor coverings, remove any coatings on the slab, and even take off baseboards. What's more, during the 72-hour test, the area cannot be disturbed. In other words, a room with a calcium chloride test underway must remain closed off for that time.

On the other hand, in situ tests require far less disruption. After drilling a few holes and placing the contained probes, that's it. There is no need to strip away existing floor coverings nor do you have to leave the area undisturbed for three days. In fact, the ASTM F-2170 testing protocol states that the area can be used for light foot traffic during the 24-hour test.


Testing for Moisture in Concrete: A Clear Choice

When it comes to measuring moisture in concrete, there is no better way than with an in situ test. Not only does this method provide more accurate readings due to its ability to measure the relative humidity inside the material itself, but it also takes less time and causes less disruption than calcium chloride tests. 

Next-Level In Situ Testing

Our MMS3 offers enhanced moisture measuring capabilities for conducting tests on any floor type. It also comes standard in our Flooring Kit: 

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