SW-04 · Subfloors & MoistureASTM F2659 covers comparative moisture readings in the upper 1.0 in. of a slab, taken with a non-destructive electronic meter.1 The guide is not intended to provide quantitative results as a basis for accepting a floor. It points to F1869 or F2170 for that.1 Its own scope uses the screening pass to decide where those additional tests go, as specified.1
A non-destructive meter sweep gives a comparative reading of moisture near the top of a slab.1 It does not show whether the slab is dry enough for a moisture-sensitive floor. ASTM F2659, the guide written for these meters, draws that line in its own scope.1
Treat the sweep as a map, not a verdict. Its job is to show where the quantitative tests belong. Trouble starts when a meter reading ends up in the file as the reason a floor went down.
What F2659 is written to do
F2659 is a standard guide for the preliminary evaluation of comparative moisture condition.1 It focuses on the upper 1.0 in. stratum of concrete, gypsum and anhydrite slabs and screeds in field tests.1 Comparative readings are usually referenced to the percentage of dry weight.1 ASTM's resilient flooring list shows the current edition as F2659-23.2
The guide names three uses:
- Determining whether moisture-related conditions on or in the slab could adversely impact resilient flooring.1
- Aiding the diagnosis of failures in installed resilient flooring. The guide says it may be used this way.1
- Determining where additional testing such as F1869 or F2170 goes, as specified. This applies where possible or when results need to be quantified.1
The guide is intended to be used with the meter manufacturer's operation instructions and interpretive data where available.1 In practice, a reading belongs to the instrument that took it. Run one meter for the whole sweep and record the model.
Why it does not replace RH or calcium chloride
F2659 says it is not intended to provide quantitative results as a basis for accepting a floor for moisture-sensitive finishes.1 It points to F1869 or F2170 for quantitative information on whether moisture levels are within specific limits.1 F1869 describes its results as directly applicable to flooring manufacturer's specifications.3 Procedures and manufacturer limits for both tests are covered in concrete moisture testing before resilient flooring.
| Method | What it measures | What it reports |
|---|---|---|
| ASTM F2659 (guide)1 | Comparative moisture condition in the upper 1.0 in. stratum1 | Comparative readings, not a basis for acceptance1 |
| ASTM F2170 (test method)4 | Relative humidity in concrete floor slabs, using in situ probes4 | Quantitative percent relative humidity4 |
| ASTM F1869 (test method)3 | Moisture vapor emission rate from bare concrete, using anhydrous calcium chloride3 | Quantitative rate, in pounds of moisture over 1000 square feet during a 24-h period3 |
All three methods describe their results as conditions at the time of the test.1 4 3 F2170 narrows it further. Results hold only for the specific locations tested.4 That point is why the sweep matters.
Slabs where the meter says little
F2659 lists conditions where its results do not provide vital information:
- Thick slabs.1
- Slabs without effective vapor retarders directly under the slab.1
- Lightweight aggregate concrete floors.1
- Slabs with curing compound or sealers on the surface.1
The guide says to consider F2170 as a more suitable method for some of these slabs. It names slabs of 6 in. plus thickness, low porosity slabs and slabs with no vapor retarder.1 The same advice covers slabs where above-surface conditions have a greater than normal influence on the moisture reduction gradient.1 A clean sweep on any of these proves little.
Lightweight aggregate is the awkward case. The meter adds little there, and F1869 says it shall not be used on floors containing lightweight aggregate.1 3 Get the accepted method in writing from the flooring manufacturer before anyone drills.
Gypsum is the other. F2659's scope includes gypsum slabs, but F1869 shall not be used on gypsum concrete.1 3 F2659 also warns that its methodology may not be appropriate for all applications. It cites the wide variation in mixtures and additives.1 For what a poured gypsum floor needs before flooring, see gypsum underlayment in multifamily floors.
Using the sweep to place the real tests
This is the use the guide was built for. The follow-up method itself comes from the project documents. F2659 refers to F1869 or F2170 testing "as specified."1
- Walk the slab first. INSTALL notes that discoloration or surface staining indicates the need for further testing.5
- Find surface treatments. F2659 may not be suitable where coatings, curing compounds or mitigation systems cannot be removed or cleaned off enough to let moisture move upward.1 F1869 shall not be used over coatings, reactive penetrants, or patching and leveling compounds.3 Mark existing patches on the plan.
- Sweep on a grid you can redraw on the floor plan. Log each reading, its location and the time.
- Mark the clusters that read high against the rest of the floor. Mark the areas that read typical, too.
- Place the specified quantitative tests in both. A probe in the driest bay only describes the driest bay.
Keep the raw log. INSTALL notes that Bluetooth-enabled meters allow real-time monitoring and automatically store data for project documentation.5 That record shows why each probe went where it did.
Where the sources disagree
Wagner Meters sells the Rapid RH concrete test. It calls in situ RH the most reliable method for assessing slab moisture.6 Wagner quotes Howard Kanare, whose research it says found the calcium chloride test fundamentally inaccurate.6 Per Wagner, Kanare found the test can give false positive and false negative results. He also found results that vary with the weather and temperature.6
F1869 describes itself differently. It calls the calcium chloride test the industry standard and a practical, well-established and accepted test of dynamic moisture.3 INSTALL lists both F1869 and F2170 as common methods for commercial concrete.5 On a given job, the documents settle the argument. INSTALL frames the goal as a substrate within the tolerances specified by the flooring and adhesive manufacturers.5
Old specifications add a wrinkle. ASTM's list shows F2420, the insulated-hood surface RH method, as withdrawn in 2014.2 It shows E1907, a guide to evaluating moisture conditions of concrete floors, as withdrawn in 2008.2 A spec that still cites either needs an answer before testing starts. See how to write a flooring RFI.
Where the money goes
INSTALL warns that unchecked moisture and high alkalinity can lead to adhesive breakdown and voided manufacturer warranties.5 It adds that poor substrate conditions can lead to last-minute material substitutions, increased labor costs and extended timelines.5 A surface-applied mitigation system is typically an epoxy or urethane coating.5 ASTM publishes practices for single-component and two-component membrane-forming mitigation systems, F3513 and F3010.2
None of that is cheap to discover after award. If the bid is silent on testing and mitigation, expect a dispute over who pays. Expect the flooring contractor to be asked first. Write both in as separate line items or clear exclusions. If a wet zone turns up after award, document it and price it through a change order.
Moisture is not the only reading. Wagner writes that ASTM International states a pH test should be performed along with every moisture test.6 ASTM's list includes F3441-24a, a guide to pH measurement for resilient installations.2 Methods and limits are in concrete slab pH before resilient flooring.
Before the meter comes out
- Ask which quantitative method the specification and the flooring manufacturer accept. Get the answer in writing.
- Ask for slab thickness, vapor retarder status and aggregate type before deciding how much the sweep can tell you.
- Map curing compounds, sealers, coatings and patches before sweeping.
- Record the meter model, grid, readings, times and site conditions.
- Label the sweep report as preliminary and comparative, not as acceptance data.
- Place quantitative tests in both high-reading and typical areas, and mark each on the plan.
- Run pH testing alongside moisture testing.
- Price testing and mitigation as line items or written exclusions.
Sources
- ASTM International, “F2659 Standard Guide for Preliminary Evaluation of Comparative Moisture Condition of Concrete, Gypsum Cement and Other Floor Slabs and Screeds Using a Non-Destr”. store.astm.org/f2659-22.html
- ASTM International, “Resilient Floor Covering Standards”. store.astm.org/products-services/standards-and-publications/standards/re
- ASTM International, “F1869 Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride”. store.astm.org/f1869-22.html
- ASTM International, “F2170 Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes”. store.astm.org/f2170-19a.html
- INSTALL (International Standard & Training Alliance), “Avoiding Moisture Mistakes in Substrate Preparation - INSTALL Floorcovering Professionals”. installfloors.org/news-events/avoiding-moisture-mistakes-in-substrate-pr
- Wagner Meters, “Avoid Flooring Problems with Accurate Moisture Testing”. wagnermeters.com/concrete-moisture-test/concrete-info/excess-moisture-in
General information for the flooring trade. This article was drafted with AI assistance and checked against the sources listed above; the manufacturer's current instructions and the project specification govern any real job. If something here is wrong or out of date, tell us.
