If you’re testing a concrete slab for moisture, the method you choose matters—and so does knowing what the results actually mean.
Two of the most common moisture tests in commercial flooring are the Relative Humidity (RH) test and the Calcium Chloride (MVER) test. Both aim to measure the moisture condition of a slab, but they work in very different ways—and choosing the wrong one can lead to faulty conclusions.
This guide breaks down both methods so you can make informed decisions on your next project.
What Is the Calcium Chloride Test?
Also known as the Moisture Vapor Emission Rate (MVER) test, this method involves placing a dish of calcium chloride on a sealed section of concrete. After 60–72 hours, the dish is weighed to determine how much moisture the slab emitted into the sealed space.
The result is expressed in pounds of moisture per 1,000 square feet per 24 hours.
Pros:
• Simple and inexpensive
• Common in older specifications
• Useful for surface-level vapor measurements
Cons:
• Only tests the top ½ inch of the slab
• Easily skewed by surface conditions or HVAC use
• Not aligned with most modern adhesive specs
What Is the Relative Humidity Test?
The in-situ RH test, standardized by ASTM F2170, measures moisture inside the slab by placing a sensor into a hole drilled to 40% of the slab depth (for slabs drying from one side). After equilibration, the sensor reads the internal relative humidity of the concrete.
Pros:
• Measures deeper into the slab—more accurate over time
• Matches how most modern flooring adhesives behave
• Widely accepted in current specifications
Cons:
• Requires drilling and waiting period
• More expensive per test than MVER
• Must be carefully installed to ASTM standards
Why the Difference Matters
Moisture-related flooring failures often happen below the surface. If you rely only on surface-level tests like calcium chloride, you might miss lingering moisture deeper in the slab—especially if the HVAC has temporarily dried the surface layer.
That’s why RH testing is now the industry standard for most commercial flooring systems. It gives a truer picture of the long-term behavior of the slab, especially in climate-controlled buildings where moisture movement is subtle but persistent.
Which Test Should You Use?
• New Construction? RH testing is almost always recommended.
• Older Spec Still Calls for MVER? Talk to the architect or GC—RH may be more appropriate.
• Time-Sensitive Project? Use a trusted testing partner who can interpret both tests in context.
Some consultants still run both tests for comparison, especially when investigating existing buildings or failure cases.
Final Word for Installers
✅ Know what test your project requires—and why
✅ Don’t assume surface dryness equals safe conditions
✅ Use qualified technicians to perform and interpret results
✅ Push for RH testing on all major installations
Good installs start with good data. By understanding the difference between calcium chloride and RH testing, you’re not just following protocol—you’re protecting the floor, the team, and your own reputation.