Concrete moisture meter

What the test measures

A handheld meter pressed on the slab reads the moisture condition near the surface. NWFA’s installation guidelines describe the method this way:

Nondestructive electrical moisture meters are the standard guide for preliminary evaluation of the comparative moisture condition of concrete, gypsum cement, and other floor slabs and screeds.

NWFA Installation Guidelines, Revised © 2025, p. 43 (PDF p. 47)¹

and say how deep it reads:

This test shows a moisture condition in the upper one-inch of the slab.

NWFA Installation Guidelines, Revised © 2025, p. 43 (PDF p. 47)¹

The meter’s figure is not an ASTM F2170 or ASTM F1869 result. It is a reading on the meter’s own scale, from the top of the slab, and meters of different makes read on different scales. The tests that do give those results are Concrete moisture test: the RH probe (ASTM F2170), which most of the documents read name, and the Calcium chloride test (ASTM F1869).

What a valid report looks like

A complete report names, at minimum:

• the method, ASTM F2659, and the meter used, with the scale it was read on;
• the date of each reading;
• where in the room each reading was taken;
• the air temperature and relative humidity in the room, and the slab’s temperature at each test area;
• each reading, test by test;
• the product or adhesive document the readings were compared with, if it gives a meter limit at all.

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

Room conditions before the test

“The interior environment of the jobsite should be 65°-85°F and 40-60% relative humidity for at least 48 hours prior to testing.”¹

Meter calibration

“To ensure accuracy, the meter should be calibrated before every project or if not used for 30 days.”¹

Number of tests

“Eight tests should be conducted for the first 1,000 square feet and 5 additional tests should be conducted for each additional 1,000 square feet with 3-5 tests per test site.”¹

Size of each test area

“Each test area should be within a one-foot-by-one-foot area.”¹

Slab temperature

“The temperature of the floor slab is to be tested and reported within 8” of each test area.”¹

What the readings are for

“These tests should be used to evaluate the surface of the concrete and to determine where to place other quantifiable tests.”¹

NWFA adds “Be sure to record the highest reading.”¹ This is NWFA’s procedure, not the floor document’s; where your product’s document describes the test, that document applies.

Red flags

Glue-down LVT: the one company’s limit, from Karndean K-99HM Adhesive Installation Guide.

NOTE: Substrate surface moisture readings (ASTM F2659) found to be above the 4% acceptable range may void the warranty.

Karndean K-99HM Adhesive Installation Guide, 240902, PDF p. 3⁶

Solid hardwood: the one company’s limit, from Bruce Solid 3/4" Strip and Plank.

Moisture readings should not exceed 4.5 on the upper scale.

Bruce Solid 3/4" Strip and Plank, LA-295726-120, © 2020, PDF p. 2⁷

What a meter reading is for, in NWFA’s words:

These tests provide useful information, but should not be used on their own to determine whether a floor should or should not be installed unless otherwise directed by the flooring manufacturer.

NWFA Installation Guidelines, Revised © 2025, p. 43 (PDF p. 47)¹

Bruce’s solid wood installation document says of the meters:

Concrete Moisture Meters give qualitative reading results-not quantitative ones.

Bruce Solid 3/4" Strip and Plank, LA-295726-120, © 2020, PDF p. 2⁷

1. Laminate: the only concrete figure on the report is a meter percentage. 2 laminate documents read do accept a meter reading, each on its own scale; both are in the table. Both name a further test for a high reading. Shaw’s Repel guide says:

   If the moisture meter readings are above 4%, have a qualified floor covering contractor perform a Calcium Chloride Moisture Emissions test.

   Shaw Repel 2G Laminate Installation, Revision: 01312022, web page²

   and Swiss Krono’s installation FAQ:

   If a less-than-favorable reading is returned it may be necessary to do a more precise test, like a calcium-chloride test, or use a meter specially designed to read moisture levels in concrete.

   Swiss Krono USA installation FAQ, web page³

2. Any floor type: the meter percentage is compared with an RH or calcium chloride limit. A meter reading is not on either test’s scale, so it cannot be held against their limits. The limit that binds you is in your product's installation document.

3. Any floor type: the report gives a reading without the meter or its scale. The limits in the table are each tied to a scale, and a figure read on another meter is not the same number.

Questions to ask the installer

1. Which meter did you use, and which scale did you read?
2. Does my product’s installation document accept a meter reading, and what does it give as the limit?
3. Was an RH probe test or a calcium chloride test run as well? Where are those results?
4. How many readings did you take for the floor area, and where?
5. What were the room’s temperature and humidity, and the slab’s temperature, when you took the readings?