The Real Costs: Calcium Chloride (CaCl) vs. RH Testing
Before finished flooring goes down, a concrete slab has to be checked for moisture, and two methods dominate the work: anhydrous calcium chloride (CaCl) testing and relative humidity (RH) testing. CaCl is widely assumed to be the cheaper of the two.
This comparison puts numbers to that assumption: materials, labor hours, and what each method actually measures.
For decades, flooring contractors have conducted moisture tests to verify the appropriate “dryness” of a concrete slab, prior to installing finished floor products. The anhydrous calcium chloride (CaCl) test provided a moisture vapor emission rate (MVER) that had been the industry benchmark since the 1940s.
In the 1990s, experts raised methodology concerns and suggested that the CaCl test did not indicate a thorough enough measure of concrete moisture condition. Since then, relative humidity (RH) testing has emerged as an alternative. Both tests may still be used, but many may ask: which one is best?
CaCl Test vs. RH: Materials
The first place most businesses would look to answer that question is cost, and on materials alone, CaCl comes out ahead.
A 10,000 square foot slab calls for 12 test locations: three for the first 1,000 square feet and one for each additional 1,000. At $11.38 per test, CaCl materials for 12 locations come to $136.56. Rapid RH® L6 Smart Sensors at $36.64 per test come to $439.68, so RH costs $303.12 more in materials. The Total Reader® used to take RH readings is reusable equipment, so it isn’t counted here.
| Materials (12 tests) | Calcium Chloride (CaCl) | Relative Humidity (RH) |
|---|---|---|
| Cost per test | $11.38 | $36.64 |
| Total for 12 tests | $136.56 | $439.68 |
| What you need | CaCl (MVER) test kits, surface grinder, vacuum, scrapers, precision gram scale | Rapid RH L6 Smart Sensors and Total Reader, ¾-inch drill bit and drill, brush and vacuum |
CaCl Test vs. RH: Time
But time equals money, too, and this is where the CaCl test falls behind.
ASTM F1869 calls for the calcium chloride test to sit for 60 to 72 hours before it can be read. This comparison uses the 60-hour minimum. ASTM F2170 calls for RH sensors, placed at 40% of the slab depth in a slab drying from the top only, to equilibrate for 24 hours before the first documentable reading.
Add the hands-on work, and RH testing at 12 locations finishes about 42 hours sooner, takes 62.5% less time from start to finish, and needs about 84% less hands-on labor.
| Test Task (12 tests) | Calcium Chloride (CaCl) | Relative Humidity (RH) |
|---|---|---|
| Prepare test locations | 60 min. | 0 min. |
| Prepare the test | 60 min. | 0 min. |
| Place the test | 60 min. | 60 min. |
| Protect the test | 111 min. | 0 min. |
| Obtain results | 120 min. | 3 min. |
| Cleanup | 18 min. | 7 min. |
| Hands-on labor | 429 min. (7 hrs. 9 min.) | 70 min. (1 hr. 10 min.) |
| Required wait | 60 hrs. | 24 hrs. |
| Total time | 67 hrs. 9 min. | 25 hrs. 10 min. |
Task times are scaled to 12 locations from the original 13-location comparison.
Here is what each step involves:
- Prepare test locations (CaCl only): scrape and grind the floor to remove debris and leave a clean surface.
- Prepare the test (CaCl only): check that the calcium chloride packages are sealed, then open them, weigh the dishes, and record the weight, date, and time.
- Place the test: for CaCl, set the dishes on the concrete, install the domes, and press them down to seal. For RH, drill the holes, vacuum out the dust, and insert the sensors.
- Protect the test (CaCl only): put up caution tape or a frame so the domes aren’t disturbed.
- Obtain results: for CaCl, cut open the domes, reweigh the dishes, and calculate the emission rate. For RH, take a reading with the Total Reader.
- Cleanup: for CaCl, scrape off the sealant and dispose of the domes, dishes, and used calcium chloride. For RH, patch each hole.
Weighing Cost Against Time and Accuracy
Put together, RH testing costs $303.12 more in materials for a 12-location slab and saves about 6 hours of hands-on labor. Those 6 hours cover the material premium only if your labor costs about $51 an hour or more, so on materials and labor alone, which test is cheaper depends on your crew’s rate.
The bigger difference is time. RH testing gets you a documentable result about 42 hours sooner, which can keep a flooring schedule on track.
The two tests also don’t measure the same thing. The CaCl test measures moisture vapor emissions at the slab surface. It does not indicate moisture levels or moisture migration through the concrete slab. RH testing measures conditions inside the slab, not just at the surface.
Measured by both time and test integrity, RH concrete moisture testing holds a long-term edge despite its higher up-front cost.
Free download: Which Rapid RH Sensor is Right For You?
Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.
Last updated on October 2nd, 2026
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