ASTM F2170 vs. ASTM F1869: Two Ways to Evaluate Concrete Moisture

ASTM F2170 and ASTM F1869 are both used to evaluate moisture in concrete floor slabs, but they do not measure the same condition. F2170 measures relative humidity inside the slab. F1869 measures moisture vapor emitted from a prepared area at the top surface during the test.

Neither standard supplies one universal pass/fail number for epoxy. The current coating manufacturer’s limit, project specification, and test-method edition determine how a result is interpreted.

ASTM F2170: an internal relative-humidity reading

F2170 requires holes in the concrete and in-situ probes placed at a depth defined by slab conditions. After the prescribed preparation and equilibration, the probe reports relative humidity and temperature in the test cavity.

The method looks below a surface that can dry faster than the rest of the slab. That makes it useful for characterizing internal moisture before the surface is covered by a low-permeability floor system.

The current standard controls:

• Number and location of tests
• Hole depth and preparation
• Probe calibration verification
• Building conditioning and test timing
• Equilibration and reading procedure
• Required reporting

Do not rely on instructions copied from an older article. ASTM lists F2170-19a as the active edition while revision work continues, and project documents may name an edition that must be reconciled before testing.

ASTM F1869: a surface emission rate

F1869 uses a weighed container of anhydrous calcium chloride beneath a sealed cover on a prepared area of bare concrete. The container absorbs moisture during the specified exposure. Its weight change is used to calculate moisture vapor emission rate in pounds per 1,000 square feet per 24 hours.

This is a surface-oriented result. It describes emission during the test conditions and at that location. The method is affected by the condition of the top portion of the slab and by the building environment.

ASTM lists F1869-23 as active. ASTM also has an active revision work item discussing limitations in using surface emission to predict the condition that can develop after an impermeable floor covers a slab. That is another reason to report what the method measures without presenting it as a forecast of every future condition.

The results cannot be converted

An RH percentage is not a moisture-vapor emission rate, and a pounds result cannot be converted into RH with a reliable universal formula. The methods observe different parts of the moisture system.

It is possible for tests on the same slab to tell different stories because:

• The surface has dried faster than the interior.
• A curing compound, sealer, old adhesive, or coating affected the top surface.
• HVAC or weather changed surface emission.
• Test locations crossed different slab or vapor-retarder conditions.
• The procedures or conditioning did not follow the current standards.

A disagreement is not solved by averaging unlike values. Verify procedure, inspect the slab, map the conditions, and consult the coating manufacturer.

How building conditions affect both tests

Concrete exchanges moisture with its environment. An unconditioned building can produce results that do not represent occupied service. Heating, cooling, dehumidification, open doors, temporary heat, recent cleaning, and weather can change the moisture gradient and surface emission.

Follow the current method and project requirements for conditioning. Record air temperature, relative humidity, slab temperature, HVAC status, test dates, and unusual events. A result without its conditions is difficult to interpret later.

Test location matters

Perimeter areas, plumbing, cracks, joints, patches, penetrations, below-grade walls, and suspected vapor-retarder damage can differ from the center of a slab. Each standard includes test-frequency requirements, and the risk survey may justify additional locations.

Map every location so a high or low reading can be connected to actual slab conditions. Do not move a planned test away from a questionable area merely to obtain a more favorable number.

Which method should be used?

Start with the complete coating system. The manufacturer may accept one method, both methods, or another documented evaluation for a specialty product. Project specifications and warranty requirements can also mandate a method.

When both are required, report them independently. F2170 provides internal RH information; F1869 provides surface emission information. Together they can add context, but neither validates the other automatically.

The broader guide to moisture testing concrete before epoxy explains how preliminary meters and water observations fit around quantitative testing.

Why there is no universal threshold

Coating systems vary in permeability, chemistry, thickness, bond, and moisture tolerance. A conventional epoxy, moisture-vapor barrier, water-based coating, breathable system, and cementitious urethane can have different acceptance limits.

Even within one product family, limits can depend on film thickness, substrate strength, pH, vapor retarder, and preparation. Use the current data for the exact assembly. If results exceed a limit, the next step may be manufacturer-approved mitigation, another system, further investigation, or postponement—not simply ignoring the highest test.

New concrete and sealed concrete

The age of a new slab does not replace testing. The article on how long before coating new concrete explains why mix, curing, thickness, enclosure, and vapor conditions matter alongside days.

Surface treatments can complicate test preparation and coating bond. Before testing or coating, determine how to tell if concrete is sealed and follow the selected standard’s requirements for a bare test area.

Moisture is not the cause of every coating change

High moisture can contribute to coating distress, but it does not explain every discoloration. Ultraviolet exposure, resin chemistry, contamination, overapplication, and thermal history can contribute to why epoxy turns yellow. Diagnose from evidence rather than assigning every defect to a moisture number.

A defensible report should include

• Standard and edition used
• Tester, date, equipment, and calibration information
• Scaled location map and slab information
• Air and slab conditions and HVAC status
• Individual results, not only an average
• Visible anomalies and deviations from the method
• The coating product limit used for comparison
• Written disposition of any result outside that limit

The bottom line

F2170 measures relative humidity within concrete. F1869 measures moisture vapor emission at the prepared surface. They are complementary tools, not interchangeable scores.

Louisville Coating Company evaluates test results against the proposed epoxy floor coating system. The correct question is not which test produces the lower number; it is which current method and limit make the specification defensible.