Calcium chloride test (ASTM F1869)

What the test measures

The test measures how much moisture leaves the surface of a concrete slab over a set time, caught in a sealed dish of calcium chloride. NWFA’s installation guidelines describe it this way:

A calcium chloride moisture test is a standard test method for measuring the moisture vapor emission rate (MVER) of a concrete subfloor using anhydrous calcium chloride.

NWFA Installation Guidelines, Revised © 2025, p. 42 (PDF p. 46)¹

How the test is run, in NWFA’s words, is under What a valid report looks like.

The result is a rate from the top of the slab, not a reading from inside it. Most of the documents read also name the RH probe test; see Concrete moisture test: the RH probe (ASTM F2170). Where a product’s document names one test, that is the test its limit belongs to.

A result means something only against a limit, and the test does not set one. The limit is in the installation document of the floor product, or of the adhesive for a glue-down floor. The table under Red flags shows how far the limits manufacturers publish spread from one floor type to the next.

What a valid report looks like

A complete report names, at minimum:

• the method, ASTM F1869;
• the date each kit was set and the date it was read;
• where in the room each kit was placed;
• the air temperature and relative humidity in the room during the test;
• each result, kit by kit;
• the product or adhesive document the results were compared with.

NWFA’s installation guidelines also set out how the test is run. Where a report says how it was run, these are the points to hold it against, quoted from NWFA:

Earliest start after the pour

“As concrete moves through its initial drying period, regular testing of moisture content to evaluate the drying condition of the slab may begin 30 days after placement.”¹

Room conditions before the test

“Ambient conditions must be 65°-85°F and 40-60% relative humidity for a minimum of 48 hours prior to conducting the test.”¹

Size of each test area

“Each prepared area must be 20”x 20,” clean, and free of all foreign substances.”¹

Preparing the surface

“Lightly grind the area to produce a surface profile equal to a concrete surface profile (CSP) 1-2, a minimum of 24 hours prior to testing.”¹

Number of kits

“Place three kits in the first 1,000 square feet and one per every 1,000 square feet thereafter.”¹

Weighing the dish

“Weigh the calcium chloride in its container.”¹

Sealing the kit

“Place the opened calcium chloride container on the prepared area and immediately cover it with a transparent cover to create an airtight seal.”¹

Time under the cover

“Let the covered container sit for 60-72 hours undisturbed.”¹

The result

“Remove the transparent cover and calculate as directed by the calcium chloride test kit manufacturer.”¹

NWFA closes the procedure with “Record the data.”¹ and adds “All tests should be performed as dictated by the most current ASTM standard.”¹ This is NWFA’s procedure, not the floor document’s; where your product’s document describes the test, that document applies.

Red flags

NWFA’s installation guidelines are an industry guideline, not the document for your product. Where the two differ, both are shown above.

1. Any floor type: the report does not name the product document its results were compared with. The limit belongs to the product, and products of one kind differ. In rigid core vinyl alone, manufacturers publish limits from 5 to 8 lb/1,000 sq ft/24 h across 4 documents. The limit that binds you is in your product's installation document.

2. Any floor type: the test was started too soon after the pour. A report that gives no pour date, or a start date earlier than NWFA’s procedure allows, cannot be held against it; NWFA’s sentence is the first point under What a valid report looks like.

3. Any floor type: fewer kits than the area calls for, or no room conditions. NWFA ties the number of kits to the floor area and sets the room’s temperature and humidity before the test; a report that leaves out the count or the room conditions cannot be held against that procedure.

4. Lightweight concrete: the test was run at all. NWFA’s guidelines say:

   ASTM has specifically disallowed ASTM F1869 for testing lightweight concrete.

   NWFA Installation Guidelines, Revised © 2025, p. 68 (PDF p. 72)¹

5. Hardwood: the result is compared with NWFA’s figure alone. For engineered hardwood and solid hardwood, NWFA’s guideline and the manufacturers’ documents give different figures; both are at the foot of the table. NWFA’s sentence:

   Concrete slabs with a calcium chloride MVER reading of greater than 3 lbs/ 1,000 square feet/24 hour are strongly recommended to wait for further drying of the slab, or install/apply a minimum class 1 impermeable vapor retarding membrane over the slab according to the adhesive manufacturer’s instructions, prior to installation.

   NWFA Installation Guidelines, Revised © 2025, p. 42 (PDF p. 46)¹

Questions to ask the installer

1. Which product’s installation document did you compare the results with, and which limit in it?
2. For a glue-down floor: which adhesive will be used, and what limit does the adhesive’s document give?
3. When was the slab poured, and when were the kits set and read?
4. How many kits did you place for the floor area, and where?
5. What were the room’s temperature and humidity before and during the test?
6. Is the slab lightweight concrete?
7. For a hardwood floor: did you compare the results with NWFA’s figure or with the product’s document?