Moisture Control Update
Note: The moisture content of a concrete slab can currently be checked by using electronic moisture meters. This method is instantaneous, inexpensive, and less costly to perform. In addition this method, using electronic surface instruments can quickly be used to evaluate each room, all perimeters, and also the field. Operating instructions are quickly and easily grasped.
The new ASTM F-2170-02 test method has two procedures for forming the hole in the concrete slab into which a relative humidity probe is placed. What appears to be the most likely method used (procedure A) is drilling a hole in the concrete then placing a hollow sleeve to line the hole. Procedure B is an alternative procedure for fresh concrete by forming a hole in concrete by placing a hollow tube in the form work then placing the concrete around the tube.
Note: As with other test methods this moisture probe test results indicate the moisture present of the slab only at the time of the test.
Tools required for the probe test are digital probe, digital meter, hole liners, rotary hammerdrill, carbide drill bits, vacuum cleaner with HEPA filter for removing drill dust from the holes.
Calibration: Probes must be calibrated within 30 days before use. You must perform 3 tests for the first 1,000 square ft. and 1 for each addition 1,000 square ft. Floor slabs must be at service temperature and relative humidity for at least 48 hours before beginning procedures. After drilling and placement of hole liner you must allow a 72 hour (3 days) period to pass before making your R/H readings.
The Electronic Users Guide recommends using the non-destructive moisture content tests be carried out until the sub-floor reaches the moisture level specified by the flooring manufacturers. Then relative humidity probe tests also can be provided to validate the non-destructive moisture content test.
As a long time advocate of the ASTM F-1869-98 moisture dome test (calcium chloride), I and many others in the industry including concrete professionals rely on this test. The main reason is the difference between moisture vapor in movement (dynamic) and moisture vapor "suspended" (static). The dome test, alone, measures moisture vapor in "movement" through the concrete slab in volume. This has always been the criteria for concern. Perhaps someone can provide data concerning the effectiveness of these other methods. This reminds me of the great debate in the flooring industry's problem of slip resistance. Do you use a static tester or a dynamic tester? This hasn't been resolved either.
ASTM F-2170-02 references the ASTM F-710 Standard of Practice for Preparing Concrete Floors to receive Resilient Flooring. I believe an alkalinity test should always be performed as a high alkaline reading (9 and up) also indicates moisture vapor is moving upwards and in addition it is the alkaline salts that attack the adhesive and flooring.
I guess we all should be happy as we now have many methods and standards of testing for moisture vapor transmission.
1. The newest one F-2170-02 In Slab Probe relative humidity
2. ASTM 1869-98 Moisture Dome Test
3. The Electronic Meter Systems (impedance or electrical)
4. ASTM E-1907 Moisture Related Acceptability of Concrete Floors
5. ASTM D-4263 Plastic Sheet Method
6. Mat or Bond Test
7. Hygrometer (R/H) on Slab
A quick review of ASTM F-110-08 covers Standard Practice for preparing concrete floors to receive resilient flooring. This standard sets the F-1869 calcium chloride test as the primary method for evaluating moisture emission but states that other test methods may be acceptable to the resilient flooring manufacturer. These methods are the rubber mal test, moisture meter testing, hygrometer, or adhesive bond test.
Another key test in F-710 is the alkalinity test on which the results should not exceed the manufacturer's recommendation. They recommend using pH paper and distilled water. Readings in excess of 9.0 are known to affect both the resilient and adhesive.
F-710 also addresses moisture retarders beneath the slab, efflorescence, flatness and levelness of the slab. In subsequent articles, we plan to address the WFCA'S white paper and provide a list of addresses for instrument manufacturers.