What ASTM F2170 and F1869 Actually Measure

ASTM F2170 and ASTM F1869 answer two different questions about the same slab. F2170, formally the “Standard Test Method for Determining Relative Humidity in Concrete Slabs Using in situ Probes,” measures the percentage of relative humidity inside the concrete mass, at a depth that represents how the slab will behave once it’s covered. F1869, the “Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride,” measures how much moisture vapor is leaving the top surface of the slab over a fixed time window, expressed in pounds per 1,000 square feet per 24 hours.

That distinction sounds academic until you’re staring at a spec sheet and a flooring warranty that don’t agree. F1869 tells you what’s happening at the surface, right now, under lab-controlled ambient conditions. F2170 tells you what’s happening deep in the slab, where moisture is still migrating outward and where it will keep affecting an adhesive or coating long after installation day. One is a snapshot. The other is closer to a forecast.

F1869: The Calcium Chloride Test, Process and Limitations

ASTM F1869 places a dish of anhydrous calcium chloride on the slab surface, seals it under a plastic dome, and leaves it undisturbed for 60 to 72 hours. The calcium chloride absorbs ambient moisture vapor; the weight gain is converted into a moisture vapor emission rate (MVER) in lbs/1,000 sq ft/24 hr. It’s a well-understood, inexpensive test with decades of field history.

Its limitations are just as well documented. Because the dome only captures the top few millimeters of slab behavior, F1869 results shift with ambient humidity, temperature, and even the time of year the test is run. A test performed during a dry, heated winter can read differently than the same slab tested in a humid summer, even though the concrete’s actual internal moisture condition hasn’t changed. The test also can’t account for moisture still migrating upward from lower in the slab, which is precisely the moisture that causes adhesive failures and flooring blisters months after installation. Industry sources have flagged these sensitivity issues as a core reason MVER results are treated with caution on moisture-sensitive jobs.

F2170: In-Situ Relative Humidity Testing, Process and Field Practice

F2170 requires drilling probe holes to 40% of the slab’s thickness for slabs drying from one side, inserting sensor sleeves, sealing them, and waiting a minimum 24 hours for the sensors to equilibrate with the surrounding concrete before taking a hygrometer reading. The 40% depth isn’t arbitrary. It corresponds to the point in the slab profile where moisture conditions best predict what will reach the top surface once a floor covering traps vapor from escaping.

Hole spacing follows a minimum-density rule: three probe locations for the first 1,000 square feet of slab, with one additional probe for each additional 1,000 square feet. That density matters because concrete moisture is rarely uniform across a large pour, so a single reading in a 50,000-square-foot warehouse floor tells you almost nothing. A properly executed F2170 test on that floor would call for roughly 53 individual probe locations, each equilibrated and read independently.

The 24-hour equilibration window is where field shortcuts happen, and where results go wrong. A probe read at hour 12 instead of hour 24 will almost always read lower than its true equilibrium value, because the sensor hasn’t fully stabilized to the surrounding concrete’s humidity. If you’re reviewing someone else’s F2170 report, the equilibration timestamps and hole-count math are the first two things worth checking.

Why the Industry Has Shifted Toward RH Testing

ASTM has formally moved away from calcium chloride testing for certain slab types. Amendments to F1869 removed the calcium chloride method as an acceptable means of measuring moisture in lightweight concrete, while F2170 was developed specifically to recognize in-situ relative humidity testing as an integral assessment method for those same slabs. Calcium chloride reads surface evaporation; RH testing reads the moisture condition at 40% depth, which is the profile lightweight aggregate concrete needs evaluated correctly because of how it retains and releases water differently than normal-weight concrete.

That standards-level shift has pushed through to the commercial side. Most flooring and adhesive manufacturers now specify in-situ RH data, sometimes exclusively, as the acceptable moisture documentation for warranty coverage. If you install a resinous coating or a moisture-sensitive adhesive system based on an F1869 reading when the manufacturer’s warranty language calls for F2170 data, you may have a compliant-looking test report and an unenforceable warranty at the same time.

F2170 vs. F1869: Side-by-Side Comparison

The table below lines up the two standards on the variables that actually drive spec decisions: what’s measured, how it’s measured, and where each one still applies. Use it to check a test report against the method a project spec or warranty actually calls for.

Which Test Fits Which Project?

Neither standard is universally “better.” Each fits specific project conditions, and the right choice depends on slab type, spec language, and how moisture-sensitive the finished floor system is.

New construction with lightweight or structural concrete over metal deck should default to F2170; it’s the only method ASTM currently accepts for that slab type, and most manufacturer warranties on these projects require RH data outright. High-risk installations, resinous flooring, moisture-sensitive adhesives, healthcare and cleanroom environments, and any high-bay warehouse floor supporting racking or automated storage systems all carry enough consequence that F2170’s deeper, more stable reading is worth the extra field time. Legacy specifications written before the industry’s shift toward RH testing may still reference F1869 by name; in those cases, follow the governing spec and document the method used clearly, since retrofitting a different test after the fact can create its own compliance headache. F1869 still has a legitimate role on lower-risk slabs, quick preliminary screening, or projects where the governing spec explicitly calls for MVER data and the concrete is conventional weight, not lightweight.

When a spec is silent or ambiguous on method, that’s a flag to raise with the design team before testing starts, not after. A pre-installation moisture testing plan that names the standard, the probe count, and the acceptance criteria in writing protects everyone on the job, including the testing firm.

Why You Can’t Convert or Cross-Walk Results Between Tests

There is no accepted conversion factor between an F1869 MVER number and an F2170 relative humidity percentage, and treating them as interchangeable data points is a documented source of spec and warranty disputes. The two tests aren’t measuring the same physical phenomenon at the same location in the slab; one is surface evaporation under a sealed dome, the other is internal humidity at a set depth. A slab can post a passing F1869 MVER reading and still carry an internal RH level that would fail a flooring manufacturer’s F2170 threshold, because the surface has dried faster than the slab core.

This matters most in a dispute. If a flooring failure occurs and the installer’s documentation shows an F1869 result while the manufacturer’s warranty required F2170 data, that mismatch alone can void coverage regardless of what the numbers actually say. The fix is procedural, not mathematical: confirm the required method in writing before testing, and never submit one test’s results as evidence of compliance with the other standard.

Getting It Right: Testing, Documentation, and Independent Verification

Moisture testing and floor flatness testing solve the same underlying problem from different angles: both replace a guess with a measured, documented number before the floor covering or racking system goes down. A slab can be perfectly flat under ASTM E1155 and still fail a floor covering installation if its moisture condition doesn’t match spec, just as a slab with acceptable moisture readings can still throw off automated guided vehicles or very narrow aisle racking if its FF/FL numbers are out of tolerance. Neither discipline substitutes for the other, and neither should be skipped to save a day of schedule.

Independent, third-party documentation matters for both. A testing firm with no product or installation stake in the outcome has no reason to round a probe reading in either direction, and that neutrality is what holds up when a warranty claim or a contract dispute lands on someone’s desk months after the concrete has cured.