Delmhorst Instrument TotalCheck - Manual (Page 26)

Copyright  2006, Delmhorst Instrument Co.
Page 26 of 32
should be evaluated in the light of factors such as type of paint, type of construction, and
climatic conditions.
The user-selectable alarm will sound if the displayed reading is above the alarm value.
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.
Taking a surface reading:
Drive two hardened-steel masonry nails about 3/4" apart into the finish coat of
concrete floor. Drive them about 1/8" deep so they make firm contact with the concrete
and do not move when touch
 Touch the nails with the contact pins.
 Press the select key and read the meter. If the meter reads less th an “68”, the
surface is dry. However, sub-surface tests should be made to verify if the slab is
dry throughout.
Subsurface test:
 Drill two 1/4" holes, 3/4" apart and 1/2" to 2" deep.
 Drive the masonry nails into the bottom of the holes and make the tests as
described above. Nails must not touch sides of drilled holes.
If the meter still indicates a “dry” condition, the floor is ready for covering. Tests
should be made at several points, especially when the slab is thick (4” or more)
and air circulation is poor. Make tests only in newly drilled holes.
Even readings in the “wet” range can indicate relatively low moisture content in
Concrete. For example, readings in the “68 to 77” range indicate approximately
2% to 4% moisture content.
When evaluating a slab for readiness, always consider its age, thickness,
whether the slab is on grade or suspended, whether a vapor barrier is present
and the drainage condition of the ground.