When it comes to flooring failures, excess moisture in the concrete slab is one of the most common—and preventable—culprits. But preventing those failures depends on choosing the right test method before installation.
Two ASTM standards dominate the conversation:
- F2170 (in-situ relative humidity testing)
- F1869 (calcium chloride moisture vapor emission testing)
They measure different things, yield different results, and aren’t interchangeable. Here’s how to decide which one is right for your project.
What Does ASTM F1869 Measure?
The calcium chloride test (MVER test) outlined in ASTM F1869 measures the rate of moisture vapor emission from the surface of a concrete slab. A dish of calcium chloride is sealed over a cleaned section of concrete, and after 60–72 hours, the weight change is used to calculate:
- Pounds of water per 1,000 sq. ft. per 24 hours (lbs/1000sf/24h)
This test reflects only the surface condition, not internal moisture.
Limitations:
• Easily influenced by surface temperature and airflow
• Not accurate for slabs with vapor retarders
• Doesn’t reflect long-term moisture behavior
What Does ASTM F2170 Measure?
ASTM F2170 uses in-situ probes to measure the internal relative humidity (RH) of a slab. Technicians drill holes to 40% of the slab depth (if drying from one side), insert sensors, and allow time for equilibration.
The test reflects actual internal moisture content, making it more predictive of how a slab will behave after flooring is installed.
Benefits:
• Aligned with how most adhesives interact with moisture
• Provides deeper insight into long-term drying trends
• Now required by many flooring manufacturers and specs
Key Differences at a Glance
| Factor | F1869 (MVER) | F2170 (RH) |
|---|---|---|
| Measures | Surface vapor emission | Internal slab humidity |
| Units | lbs/1000 sf/24 hr | % Relative Humidity |
| Depth of Insight | Surface only | 40% slab depth |
| ASTM Standard | F1869 | F2170 |
| Industry Preference | Declining | Increasing (preferred standard) |
| Best For | Older slabs, basic screening | New builds, modern adhesives |
Which Should You Use?
✅ Use F2170 for most new construction projects, especially when adhesives or moisture-sensitive finishes are involved.
✅ Use F1869 only when required by legacy specs or manufacturers—and never as the sole testing method on critical installations.
✅ Never mix test types to determine compliance. Results from F1869 and F2170 do not correlate and cannot be converted.
Final Word for Contractors and Designers
Moisture testing isn’t one-size-fits-all. The right method depends on slab age, finish system, and performance goals. When in doubt, RH testing provides the most reliable path to warranty compliance and long-term success.