Copyright
2011, Delmhorst Instrument Co.
Page 10 of 17
represent the relative dryness or wetness of the material on a scale of 5 to 60. In order to
accurately interpret your readings, first establish a baseline reading by taking a reading in an
area you know to be unaffected, then take a reading in the affected area and compare the
two readings.
MEASURING RELATIVE HUMIDITY IN CONCRETE FLOOR
SLABS IN ACCORDANCE WITH ASTM STANDARD F2170:
Select test locations to provide information about moisture distribution across the entire concrete
slab, especially areas of potentially high moisture, or if the slab is thick (>4 in.) and air circulation
is poor. For slabs on-grade and below-grade, include a test location within 3ft of each exterior
wall. Perform minimum three tests for the first 1000 ft sq and at least one additional test for each
additional 1000 ft sq.
1. Drill a 5/8” hole to a depth of 40% of the slab thickness using a rotary hammer drill. Use a
drill bit specially designed for rotary drills and with 3 or 4 cutting edges to insure a
smooth, round hole. Surface preparation is not required.
2. Vacuum the hole thoroughly, then use a wire brush to clean and loosen any concrete
remaining in the hole. Vacuum again and repeat the process a second time.
3. Insert the yellow sleeve (sold separately) into the hole. use silicone (or other water-
resistant sealant) to seal the interface between the collar of the sleeve and the concrete
surface
.
Use a hammer to insure the sleeve is fully inserted into the hole and sealed to
the concrete.
4. Insert the protective yellow cap into the sleeve and let the hole acclimate for 72h.
5. Remove the cap and immediately insert the sensor to full hole depth. Wait a minimum of
1h and then take RH readings by connecting one end of the RH/T-C1 cable to the top of
the meter and the other end to the exposed connector on the sensor housing. Check to
ensure the meter’s displayed RH reading is no long changing. The reading must not
change more than 1% RH over 1 hour. If the reading does change, allow more time for
acclimation.
6. Alternately, insert the RH sensor into the sleeve immediately after setting the sleeve.
Readings can then be taken as soon as the hole has acclimated.
The complete ASTM document is available at:
http://www.astm.org/Standards/F2170.htm
TESTING CONCRETE SLABS FOR FLOORING APPLICATIONS
Moisture meters are an effective tool to check moisture in concrete. They can tell you where there
may be excess moisture and help determine if you need to conduct further testing.
It is important to test both the surface and mid-section of the slab, especially if the slab is on or
below grade. This will help determine if there is continuous moisture migration toward the
surface. If this condition exists, the moisture movement may be so slow that once it reaches the
surface, moisture evaporates and causes a “dry” reading when a surface test is made.
However, if a sub-surface test is made, the meter may read “wet” indicating the presence of
moisture. When the slab is covered and the upward movement of moisture continues, moisture
will move into a hygroscopic (wood) floor, or build-up pressure under a non-breathing synthetic
floor, causing delamination.