6
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:
The 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. ***
Is the slab on grade or suspended?
If the slab is on grade, is there an effective vapor barrier under the slab?
How thick is the slab?
What is the drainage condition of the ground?
History of other structures in the area
***Taken from Section V Appendix AA
“Moisture Testing Procedures for Concrete Slabs” — NWFA
Testing Brick or Concrete for Paint Application
Brick, stucco, or concrete surfaces must be dry at the time of application and must remain dry after paint is applied or failure of the
paint film may occur. These materials are frequently exposed to unusual moisture conditions that allow them to absorb moisture
through some exposed surface or some structural defect. This is why it is important to check the moisture content of the brick or
concrete when it has been exposed to conditions that permit it to absorb moisture.
Procedure:
Drive two hardened steel masonry nails
about 19mm (
¾”) apart into the brick or concrete. Drive them about 6.4mm
(¼”) deep so they make firm contact and do not move when touched.
Touch the nails
with the contact pins
.
Press read button
and read the reference scale
.
Normally, dry concrete or brick will read in the green or “dry” portion of scale, indicating a safe condition to apply paint. Meter
readings should be evaluated in relation to other factors
— knowledge of the structure, type of paint used, expected weather
conditions in the near future, etc. Paint should not be applied if
readings are in the red or “wet” portion of the scale.
Do not be misled by surface appearance of masonry materials. Short exposure to rain may thoroughly wet the surface while the
interior is still dry. In this instance, we recommend repeating the test on the masonry
below the surface
as mentioned above.
Key Areas to Check:
The rear side of brick parapet walls
—
generally are not waterproof above the flashing line and frequently absorb
moisture during rains.
Painted concrete floors on ground
—
subject to peeling as they absorb moisture from the earth, unless an effective
vapor barrier has been installed.
Tests on these materials should be made a day or so after they have been exposed to rain or other high moisture conditions to
verify to what extent they absorb moisture.
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