ASTM F1869 — Calcium Chloride Test
ASTM F1869 measures how much moisture vapor is coming out of a concrete subfloor, using anhydrous calcium chloride sealed under a dome for a set period.
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It reports a moisture vapor emission rate at the slab surface, which makes it a companion to in-situ RH testing rather than a replacement for it.
Key facts
| Measures | Moisture vapor emission rate at the slab surface |
|---|---|
| Method | Anhydrous calcium chloride under a sealed dome |
| Companion method | ASTM F2170 (in-situ relative humidity) |
| Referenced by | NWFA Wood Flooring Installation Guidelines |
What this test tells you that F2170 does not
It quantifies what is actually leaving the slab surface, which is the moisture an adhesive or a floor covering has to contend with.
Because it measures at the surface, it is sensitive to conditions in the room during the test. Both methods are used because they answer different questions, and a specification that names one does not automatically satisfy the other.
How the two tests are used together
In-situ RH characterizes the slab's interior condition; calcium chloride characterizes what is emerging at the surface under current room conditions.
Where a manufacturer's warranty names a specific test, that test is the one that has to be run. Substituting a different method because it is faster is how warranty claims get denied.
Frequently asked questions
Which slab moisture test should be used?
Whichever one the flooring or adhesive manufacturer specifies. Where nothing is specified, in-situ RH under ASTM F2170 characterizes the slab's interior condition more completely.
Can both tests be run on the same slab?
Yes, and on a difficult slab both are often run, because they answer different questions about the same concrete.
Does a passing test mean I can skip the vapor retarder?
No. Whether a vapor retarder is required is determined by the assembly and the manufacturer's instructions, not only by a single moisture reading.
Sources & references
- ASTM F1869 — Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride — https://www.astm.org/f1869-23.html
- NWFA Wood Flooring Installation Guidelines — https://nwfa.org/wp-content/uploads/2026/02/NWFA-Installation-Guidelines.pdf
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