Delmhorst Instrument BD-10 - Manual (Page 8)

If the meter still indicates green or “dry” the floor is ready
for covering. Tests should be made at several points,
especially when the slab is thick and air circulation is poor.
Tests should only be made in newly drilled holes, since the
inside surface of the holes can dry out while the rest of the
slab is still wet.
Even readings in the red or “wet” area can indicate
relatively low moisture content in concrete. For example,
readings in the 85-95 range on the reference scale
$
indicate approximately 2% to 4% moisture content.
If more testing is required, the calcium chloride test is
recommended, which measures the moisture vapor emission
rate of concrete. The National Wood Flooring Association
offers the following guidelines when evaluating the results
of the calcium chloride test***.
Key Factors to Consider:
hThe age of the slab. National Wood Flooring Association
guidelines specify to wait at least 30 days after the slab
is laid before checking moisture content. ***
hIs the slab on grade or suspended? If the slab is on
grade, is there an effective vapor barrier under the slab?
hHow thick is the slab?
hWhat is the drainage condition of the ground?
hHistory of other structures in the area
***Taken from Section V Appendix AA “Moisture Testing
Procedures for Concrete Slabs” — NWFA
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Results Indicate
0-3 lbs. Dry
over 3 lbs. Moisture barrier required
over 7 lbs. Too wet