Concrete Moisture Testing: In-Situ RH (ASTM F2170) and Calcium Chloride (F1869)

Concrete moisture testing measures how much water a slab still holds or releases before a moisture-sensitive floor, coating or membrane is applied, by in-situ RH under ASTM F2170-19a or calcium chloride under ASTM F1869-23. Neither test method sets a pass value: the maker of the product on top, or the project specification, sets the limit.

F2170 reports relative humidity inside the slab in percent, and F1869 reports a moisture vapor emission rate in lb/1,000 ft²/24 h, where 1 lb/1,000 ft²/24 h equals 4.88 g/m²/24 h. Resin floors, coatings, screeds and tile membranes each carry their own limit in the data sheet, which makes the test a hold point for the families of construction chemicals that go onto a slab.

Three further methods screen or supplement the two US tests: the ASTM D4263-24 plastic sheet practice, electronic meters under ASTM F2659-23 and the carbide (CM) method of EN 13892-10:2025 for European screeds. Surface pH is a separate check that ASTM F710-26 requires. Limits range from 75 % RH for UK screeds under BS 8204-7:2003 to below 100 % RH for Ucrete 33 NA, and US RH testing costs USD 250 to 300 per test location (Mohawk Group, 2026-07).

The summary table below lists the methods, units and owners of the limits.

Standards, codes and regulations are checked against their issuing bodies, product values against the named data sheet and prices against the dated source named in the sentence; see our methodology and fact-checking.

What Does Concrete Moisture Testing Measure, and Why Is It Required?#

A moisture test tells the specifier whether a slab is dry enough for the product on top, because resin floors, coatings, screeds and resilient flooring each carry a moisture limit. That limit sits in the product data sheet or the project specification, never in the test method. Cementitious products, such as repair mortars, tile mortars and grouts, take the opposite condition: manufacturer practice places them on saturated surface-dry concrete with no standing water.

Which document makes the test mandatory? ASTM F710-26, the Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring (active since 2026-09-09), requires moisture testing of all slabs and pH testing of all floors. Moisture testing sits beside surface profile, pull-off and dew-point checks among the application and test methods for construction chemicals.

Relative humidity, emission rate and moisture content are different quantities#

In-situ RH is the relative humidity inside the slab in percent, MVER is the mass of water vapor leaving the surface per area and day, and moisture content is the water share in percent by weight. The three numbers do not convert into one another, so a limit written in one unit is checked only with the method that produces that unit.

A UK screed shows the split: BS 8204-7:2003 accepts a calcium sulfate screed under impermeable floorings at 0.5 % w/w moisture content, under permeable floorings at 1.0 % w/w, or at 75 % RH. The table below compares the five quantities a moisture report can contain.

Which Standards Govern Concrete Moisture Testing, and Which Editions Are Current?#

Six ASTM documents govern concrete moisture and pH testing in the US, all active in October 2026: F2170-19a, F1869-23, D4263-24, F2659-23, F710-26 and D4262-05(2024). In Europe, the carbide (CM) method of EN 13892-10:2025, the German screed standard DIN 18560-1:2021 and the UK code of practice BS 8204-7:2003 govern screed moisture.

The table below lists every document with its edition, status date and what it contains on pass or fail.

Each test document sets how to measure, not what passes; further ASTM and EN documents are listed under standards for construction chemicals.

Withdrawn documents still copied into specifications#

Four citations in older specifications point to documents that are withdrawn or superseded. The four are listed below.

• ASTM E1907-06a, the former guide to evaluating moisture conditions of floors for resilient coverings: withdrawn in 2008; the practice that replaced it is now ASTM F710-26.
• ASTM F2420: withdrawn in 2014.
• ASTM F2170-18 and F2170-11: superseded by F2170-19a, the only active edition in the ASTM catalog on 2026-10-22; no "F2170-23" exists.
• ASTM D4263-83(2018): historical, replaced by D4263-24, now a Standard Practice.

How Is the In-Situ Relative Humidity Test (ASTM F2170) Run?#

ASTM F2170-19a measures relative humidity inside a concrete floor slab with probes placed in drilled holes, read once each probe has come to equilibrium with the concrete around it. Its full title is "Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes", and the ASTM store page, last updated on 2020-01-09, lists no newer edition as of October 2026.

A specification cites F2170-19a by its edition and leaves hole depth, building conditioning, equilibration time and the number and position of test locations to the standard text and to the testing agency that applies it. A report that works to F2170-18 or F2170-11 does not meet a specification that names F2170-19a, because both earlier editions are superseded.

Relative humidity and emission rate answer different questions. F2170 reads the condition inside the concrete at the probe, while F1869-23 reads the vapor that leaves the prepared surface under a dome, and F1869 cannot be run on gypsum or lightweight aggregate floors. Product data sheets name F2170 directly: Sikafloor 315 accepts a slab RH of 85 % or less, and Ucrete 33 NA accepts below 100 % RH. Both limits belong to resin and industrial floor coatings for concrete, the product group whose data sheets carry these RH limits.

How Is the Anhydrous Calcium Chloride Test (ASTM F1869) Run?#

ASTM F1869-23 measures the moisture vapor emission rate (MVER) of a concrete subfloor by weighing the moisture that a dish of anhydrous calcium chloride absorbs under a sealed dome. The result is reported in lb/1,000 ft²/24 h, the inch-pound unit the standard treats as primary, and 1 lb/1,000 ft²/24 h equals 4.88 g/m²/24 h (453.59 g over 92.903 m²). The full title, "Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride", has been active since its update on 2023-09-14. A test-equipment maker's summary puts the exposure at 60 to 72 hours before the dish is reweighed; the standard text governs the exact window.

The F1869-23 scope excludes five situations: gypsum concrete, lightweight aggregate floors, and tests through coatings, reactive penetrants, or patching and leveling compounds. The report therefore records the floor type and the surface condition at each dome.

The chloride content of hardened concrete is a different question from calcium chloride emission testing, answered by acid-soluble and water-soluble methods under chloride testing of concrete.

Which Other Moisture Methods Exist, and What Are They Good For?#

Three further methods sit beside F2170 and F1869: the plastic sheet practice, electronic meters and the carbide (CM) method. The first two screen a slab; the CM method gives a moisture content in percent by weight, which DIN 18560-1:2021 makes the contractual residual-moisture method in Germany.

Plastic sheet method (ASTM D4263)#

ASTM D4263-24, a Standard Practice since its 2024-06-10 edition, indicates capillary moisture by taping a plastic sheet to the concrete surface before coating. FDOT Dev403EO (rev 2020-08-11) requires a D4263 test of at least 5 hours before epoxy overlays, a specification value for that agency's own work. The Sikafloor-264 N data sheet asks for no rising moisture by a polyethylene-sheet test before the epoxy goes on.

Electronic moisture meters (ASTM F2659)#

ASTM F2659-23 is a guide for a preliminary evaluation of concrete moisture with non-destructive electronic meters, so a meter reading screens a slab but is not an acceptance result. A meter survey shows where a slab reads wetter or drier; acceptance still rests on the method that the product data sheet names.

Carbide (CM) method under EN 13892-10 and DIN 18560-1#

The carbide (CM) method of EN 13892-10:2025 tests a screed sample with a 7 g calcium carbide ampoule and reads the moisture content after 10 minutes. The sample weighs 50 g for cementitious (CT) and magnesite (MA) screeds and 100 g for calcium sulfate (CA) screeds. DIN 18560-1:2021, which replaced the 2015 edition, makes the CM method the contractual residual-moisture method for screeds in Germany and leaves readiness values per floor covering to trade guidance. As a product example, the Sikafloor-264 N data sheet sets substrate moisture at 4 % by weight or less, measured by Sika-Tramex, CM or oven-dry method.

How Is Surface pH Tested Before Flooring and Coatings?#

Surface pH is tested because fresh concrete is strongly alkaline, with a pore solution of pH 13 to 13.8, and ASTM F710-26 requires a pH test on every floor receiving resilient flooring. The acceptable range comes from the maker of the adhesive, coating or flooring, in the same way as the moisture limit.

ASTM D4262-05(2024), the test method for pH of chemically cleaned or etched concrete surfaces (updated 2024-06-26), determines only whether a surface is acidic or alkaline after etching or cleaning, which confirms that residues were rinsed off. Sherwin-Williams surface preparation guidance asks for a final pH of 10 or higher after rinsing, a manufacturer value rather than a D4262 requirement. Mechanical preparation avoids acid residue altogether, and the profile it leaves is graded under concrete surface profile.

What Moisture Level Is Acceptable for a Concrete Slab?#

There is no single acceptable moisture level for a concrete slab: each product sets its own, from 75 % RH for UK screeds under BS 8204-7:2003 to below 100 % RH for Ucrete 33 NA. A UK screed is a code-of-practice case, not a product: BS 8204-7:2003 treats screeds as ready for floorings at 75 % RH, and calcium sulfate screeds at 0.5 % w/w moisture under impermeable floorings or 1.0 % w/w under permeable ones.

Where the maker gives no figure, 14.6 g/m²/24 h (3 lb/1,000 ft²/24 h) by F1869 is a common default in industry practice, never an ASTM requirement. The pool membrane row in the table below shows the two-unit form, with one limit for each method in the same data sheet. A limit is therefore read in three parts: the method, the number with its unit, and the document that owns it.

The table below lists limits that name their product or document.

Limits belong to the named product or document; the ASTM methods set none.

Why ASTM F2170 and F1869 set no pass or fail value#

ASTM F2170-19a and F1869-23 are test methods, so they describe how to measure and report and leave the limit to the product data sheet or the project specification. A claim that 75 % RH is "the standard" mixes two documents: 75 % RH is the BS 8204-7:2003 readiness value for UK screeds, not an ASTM figure. The same holds for 3 lb/1,000 ft²/24 h, a default for products without their own limit. ASTM F3010-24 shows the logic from the other side, applying only when F1869, F2170 or F2420 results exceed the flooring or adhesive limit.

How Are Moisture Results Read and Reported?#

A moisture report is usable only when it names the method and edition, every test location, the slab type, each reading in its own unit and the product limit it is compared with. The six items below make a report checkable against the specification.

1. Method and edition, for example ASTM F2170-19a or F1869-23, never a superseded edition.
2. Test locations marked on a floor plan.
3. Slab type: on grade, suspended, lightweight aggregate or gypsum, the last two being outside the F1869 scope.
4. Each reading with its unit, and MVER in both units (1 lb/1,000 ft²/24 h = 4.88 g/m²/24 h).
5. The product and its limit, with the document the limit comes from.
6. Test date and the testing agency or applicator who ran it.

What Are the Common Errors in Slab Moisture Tests?#

Seven errors invalidate slab moisture results, and each one changes the reported number without any change in the slab. The seven errors are listed below.

1. F1869 domes placed on gypsum floor underlayments or lightweight aggregate floors, or over coatings, reactive penetrants, patches or leveling compounds, all outside the F1869-23 scope.
2. A meter reading used as acceptance, although ASTM F2659-23 treats meters as a preliminary evaluation.
3. 14.6 g/m²/24 h (3 lb/1,000 ft²/24 h) read as an ASTM requirement instead of a default where the maker gives none.
4. Superseded or withdrawn citations: F2170-18, F2170-11, a non-existent "F2170-23" or E1907, withdrawn in 2008.
5. Air RH confused with slab RH: ISO 8502-4:2017 judges 85 % air RH or more critically and asks for a substrate at least 3 °C (5.4 °F) above the dew point, and the Sikafloor-264 N data sheet limits application to 80 % air RH; neither is a slab moisture value.
6. Forced drying of cement screeds or concrete bases, which BS 8204-7:2003 excludes; it allows forced drying only for calcium sulfate screeds from 7 days.
7. Blisters blamed on slab moisture that come from air released by the concrete, covered under outgassing in concrete floor coatings.

Which Product Classes Call for a Moisture Test?#

Seven product classes on this site carry a moisture or pH condition in their data sheets or standards, and each links to the test it needs. The seven classes are listed below.

1. Epoxy flooring: RH by ASTM F2170-19a or MVER by F1869-23, with the limit in the data sheet, for example 85 % RH or less for Sikafloor 315.
2. Polyurethane cement floors: high RH tolerance, with Ucrete 33 NA accepting below 100 % RH by F2170.
3. Self-leveling underlayments: the slab and the underlayment are each held to the limit of the product placed on them.
4. Floor screeds: 75 % RH under BS 8204-7:2003 and the CM method under DIN 18560-1:2021.
5. Concrete primers for coatings and resin floors: moisture-tolerant primers chosen against the F2170 or F1869 result.
6. Tile adhesives and tile installation systems: pool waterproofing membranes, whose data sheets can state an MVER or an RH limit (see the acceptance table).
7. Protective coatings for concrete: F1869, F2170 or the D4263-24 plastic sheet before coating, as the data sheet names.

What Does Moisture Testing Cost, and Who Runs It?#

RH testing costs USD 250 to 300 per test location in the US, and 12 probes on 929 m² (10,000 ft²) cost USD 3,000 to 3,600, per Mohawk Group guidance dated 2026-07. Both are testing figures from the same dated source; mitigation and flooring work are priced separately.

The test is run by the flooring or coating applicator or by an independent testing agency named in the specification, and the report goes to the specifier before application. Air temperature, air RH and the dew-point margin on the day of application are a separate check from slab moisture, made with the dew point calculator for coating application.

Where Moisture Testing Fits Before Mitigation and Coating#

A moisture test is the gate between slab preparation and the product on top: a slab within the product limit goes ahead, and a slab above it dries longer or receives a moisture mitigation system. Mitigation membranes under ASTM F3010-24 apply only when F1869, F2170 or F2420 results exceed the flooring or adhesive limit, and the standard excludes gypsum-based substrates.

What lies below the slab changes how fast it reaches a product limit, as the drying figures in the first question below show.

Concrete moisture testing FAQs#

How long does a concrete slab take to dry?#

Drying time depends on the water-cement ratio, the slab thickness and whether the slab is sealed below. In Graniterock tests at 23 °C (73 °F) and 50 % RH, a 0.50 w/c slab took 82 days to reach 14.6 g/m²/24 h (3 lb/1,000 ft²/24 h) when sealed below against 144 days unsealed, and a 0.40 w/c slab took 46 against 52 days. BS 8204-7:2003 warns that 150 mm (6 in) concrete bases can take more than a year to dry from one face, and calcium sulfate screeds dry at 1 day per mm up to 40 mm plus 2 days per mm beyond, at 20 °C (68 °F) and below 65 % RH. The layer below the slab is covered under under-slab vapor retarders.

What does a 99 % RH reading mean?#

A 99 % RH reading means the slab is close to saturated at the probe; whether it passes depends only on the product. Ucrete 33 NA accepts below 100 % RH by F2170, so 99 % passes, while Sikafloor 315 needs 85 % RH or less, so 99 % fails.

Can a pin or pinless meter replace an RH or calcium chloride test?#

No: ASTM F2659-23 treats electronic meters as a preliminary evaluation, so the acceptance test is F2170, F1869 or another method the product data sheet names.

What happens when a slab fails the moisture test?#

A slab above the product limit is left to dry longer or receives a moisture mitigation system. ASTM F3010-24 membranes are rated at 0.10 perm or less by ASTM E96 Procedure B, and selection is covered under moisture mitigation systems for concrete slabs.

Is the calcium chloride in the test the same as in concrete?#

No: in ASTM F1869-23, anhydrous calcium chloride is a desiccant sealed in a dish on the slab surface and never enters the concrete mix. Calcium chloride used as a set accelerator in concrete mixes is a separate topic, not covered here.