What the Calcium-Chloride Test Measures

The anhydrous calcium-chloride test is described in ASTM F1869. It provides a quantitative measurement of the moisture-vapor-emission rate from the surface of a bare concrete floor.

The result is commonly called the MVER, or moisture-vapor-emission rate. It is reported as the equivalent number of pounds of water emitted from 1,000 square feet of concrete during a 24-hour period.

The test uses a preweighed quantity of dry, anhydrous calcium chloride placed beneath a sealed cover. The calcium chloride absorbs moisture emitted from the prepared concrete surface. After the required exposure period, the material is reweighed. The increase in weight is used to calculate the emission rate.

What the Test Result Means

An MVER result provides a numerical indication of how much moisture vapor is leaving the prepared test area during the test period. The result can be compared with a published maximum established by the flooring, adhesive, coating, primer, or moisture-mitigation manufacturer.

ASTM F1869 does not establish one universal passing limit for every product. One system may permit a higher emission rate than another. The contractor must identify the acceptance limit for the complete proposed assembly.

Where ASTM F1869 Can Be Used

The method applies to bare concrete floors located below grade, on grade, and above grade. However, the standard includes important limitations.

The Test Should Not Be Used

• On gypsum concrete
• On floors containing lightweight aggregate
• Over an existing coating
• Over a reactive penetrating treatment
• Over patching or leveling compounds
• On an improperly prepared or contaminated test surface
• As a substitute for another test method required by the specification

If the existing flooring, coating, adhesive, patching material, or curing compound has not been removed from the test area, the result may reflect the behavior of that material instead of the bare concrete.

Surface Preparation Is Essential

The test area must expose clean, bare concrete. Coatings, adhesives, curing compounds, sealers, residual flooring, patching materials, dirt, oil, and other materials can restrict moisture movement or interfere with the test.

Preparation should be performed within the dimensions and time requirements of the current ASTM procedure. The selected method must remove surface materials without adding water or chemicals that could distort the result.

Common Preparation Problems

• Testing over adhesive residue or curing compound
• Using chemical cleaners that leave residue
• Wet cleaning immediately before the test
• Preparing an area smaller than required
• Placing the test over a patch or leveling compound
• Failing to allow the prepared area to stabilize as required
• Leaving dust that prevents the cover from sealing properly

Building Conditions Affect the Result

Moisture emission from a concrete surface is influenced by temperature, relative humidity, airflow, and HVAC operation. Testing in an open, unconditioned building may produce a result that does not represent normal service conditions.

The building should be maintained at the service temperature and relative humidity required by the current standard and project documents before and during testing. Record whether the HVAC system is operating normally and whether exterior doors or windows are open.

Environmental Information to Record

• Ambient temperature
• Ambient relative humidity
• Concrete surface temperature
• HVAC operating condition
• Duration of building conditioning
• Recent rain, flooding, cleaning, or water exposure
• Unusual airflow, direct sunlight, or temporary heating

Selecting the Test Locations

Test locations should represent the floor area and its varying conditions. Do not place all tests in the driest, most convenient, or most accessible areas.

The standard establishes a minimum number of tests based on floor area. The commonly applied minimum is three tests for the first 1,000 square feet and one additional test for each additional 1,000 square feet.

More tests may be required by the project specification, manufacturer, owner, or site conditions. Additional locations may be appropriate near exterior walls, drains, cracks, plumbing, wet areas, previous failures, and different concrete placements.

Basic Testing Procedure

1. Review the requirements. Confirm the governing ASTM edition, required number of tests, product limits, building conditions, and tester qualifications.
2. Develop a location plan. Give every test a unique identification number and mark its location on a floor plan.
3. Expose bare concrete. Remove coatings, adhesives, curing compounds, sealers, patching, and other interfering materials from the required area.
4. Prepare and clean the test area. Follow the current standard without adding moisture or leaving surface contamination.
5. Record the initial kit weight. Use the weight supplied or obtained according to the approved test-kit procedure.
6. Open and place the calcium-chloride dish. Avoid contamination, unnecessary exposure to room air, and direct contact with the test material.
7. Seal the cover to the concrete. The enclosure must prevent room air from entering the test chamber.
8. Record the start time. Protect the enclosure from disturbance, damage, direct sunlight, water, and unauthorized removal.
9. End the test within the required exposure period. Follow the current ASTM procedure for test duration.
10. Seal and reweigh the container. Record the final weight accurately and calculate the MVER.
11. Report the result. Include the location, duration, environmental conditions, calculations, equipment, and applicable acceptance criteria.

Test Duration

The calcium-chloride dish must remain beneath the sealed cover for the exposure period required by the current ASTM F1869 procedure. The commonly specified period is between 60 and 72 hours.

A test stopped too early or left in place beyond the permitted time does not comply with the procedure. Record the installation and removal times precisely rather than describing the duration as approximately two or three days.

The Importance of an Airtight Seal

The enclosure isolates the calcium chloride and test area from the surrounding room. If the cover is not sealed securely, the calcium chloride may absorb moisture from ambient air rather than only the moisture emitted from the concrete test area.

Dust, surface irregularities, damaged sealant, foot traffic, cords, hoses, and cleaning equipment can compromise the enclosure. Inspect the seal during placement and again when the test is collected.

How the Result Is Calculated

The calculation uses the increase in calcium-chloride weight, the area enclosed by the test cover, and the exact exposure time. The result is normalized to 1,000 square feet over 24 hours.

Approved test kits may provide calculation instructions or a reporting system. The technician remains responsible for recording accurate weights and times and confirming that the correct test-area value is used.

Rounding, transcription, unit-conversion, and decimal-placement errors can significantly change the reported result. Calculations should be reviewed before the report is issued.

Interpreting MVER Results

ASTM F1869 Versus ASTM F2170

Calcium-chloride testing and in-situ relative-humidity testing do not measure the same property. Their results should not be converted or treated as interchangeable.

Limitations of the Calcium-Chloride Test

• It reflects surface emission during the test period.
• It does not directly measure internal slab relative humidity.
• It does not identify the moisture source.
• It does not prove whether an underslab vapor retarder is present.
• It does not establish whether hydrostatic pressure exists.
• It does not evaluate condensation risk by itself.
• It is affected by surface preparation and environmental conditions.
• It cannot be used over coatings, patches, or leveling materials.
• It is not intended for gypsum concrete or lightweight-aggregate floors.
• It represents the condition at the tested locations and time.

Common Testing Mistakes

• Testing before the building reaches required service conditions
• Using fewer tests than required
• Testing over adhesive, sealer, coating, or curing-compound residue
• Preparing the surface with water or a residue-producing chemical
• Installing the test too soon after surface preparation
• Failing to seal the enclosure completely
• Leaving the test in place for the wrong amount of time
• Placing the kit in direct sunlight or near unusual airflow
• Using inaccurate or unverified weighing equipment
• Failing to record exact start and stop times
• Using the wrong enclosure area in the calculation
• Comparing the result with a limit for a different product

Reporting the Test

A complete report should allow the project team to determine whether the test was performed correctly and whether the result applies to the proposed installation.

Include the Following Information

• Project name, address, and test area
• Name and qualifications of the testing technician
• ASTM standard and edition used
• Floor area and required number of tests
• Test identification number and mapped location
• Surface-preparation method and preparation date
• Initial and final calcium-chloride weights
• Test-enclosure area
• Exact start and stop dates and times
• Calculated exposure duration
• Ambient temperature and relative humidity
• HVAC and building-service conditions
• Calculated MVER result
• Applicable manufacturer or project acceptance limit
• Any disturbance, unusual condition, or procedural exception

Safety and Handling

Anhydrous calcium chloride readily absorbs moisture. Avoid unnecessary exposure to room air and follow the test-kit manufacturer's handling instructions. Wear appropriate eye and skin protection and review the supplied safety information.

Mechanical preparation of the test area may create respirable crystalline silica. Follow applicable OSHA requirements, use effective dust collection and HEPA-filtered equipment, and wear required personal protective equipment.

Protect test kits from foot traffic and equipment. Use visible barriers or markings without changing the air movement or temperature around the enclosure.

Contractor Pre-Test Checklist

• Obtain the current ASTM F1869 procedure.
• Confirm that the slab type is eligible for the test.
• Verify required tester qualifications.
• Confirm building service conditions and conditioning period.
• Calculate the required number of test locations.
• Prepare a representative test-location map.
• Identify the complete system's published MVER limit.
• Expose clean, bare concrete using an approved preparation method.
• Confirm that the test kits and weighing equipment are suitable.
• Record exact installation and collection times.
• Inspect every enclosure for an airtight seal.
• Prepare a complete test report before approving installation.

Knowledge Check

Technical References

Use the edition required by the project specification and verify that testing personnel have access to the complete current procedure.

• ASTM F1869-23 - Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.
• ASTM F2170 - Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In Situ Probes.
• ASTM F710 - Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring.
• ASTM F2659 - Standard Guide for Preliminary Evaluation of Comparative Moisture Condition of Concrete, Gypsum Cement, and Other Floor Slabs and Screeds Using a Non-Destructive Electronic Moisture Meter.
• ICRI Concrete Slab Moisture Testing Program - Education and certification for technicians performing standardized concrete slab moisture tests.
• OSHA 29 CFR 1926.1153 - Respirable Crystalline Silica standard for construction.
• Current technical data sheets and installation instructions issued by the specified coating, flooring, adhesive, primer, and moisture-mitigation system manufacturers.

These references provide technical guidance but do not replace the project specification, applicable regulations, manufacturer requirements, or evaluation by a qualified professional. Final testing, product-selection, and installation decisions must be based on current documents and actual site conditions.