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Measuring Moisture in Walls

May 15, 2012

Excessive moisture in masonry
or concrete walls at the time
of sealing or painting can
destroy the performance of
coating systems by interfering
with film formation, adhesion,
and/or inhibiting the cure of the coating.
Masonry and concrete surfaces may
appear to be dry by sight and touch prior to
coating application but still contain detrimental
levels of moisture within the substrate.
Even when the substrate is dry at the
time of application, subsequent moisture
intrusion in service can cause blistering and
detachment of the film (Photo 1).
While there is little controversy regarding
the detrimental effects of moisture on
coatings, there is substantial confusion
when selecting the method(s) for measuring
the moisture content and interpreting the
results. Note that the Society of Protective
Coatings (SSPC) is tackling this issue headon
in 2012 through its newly formed
Commercial Coatings Committee. One of
the immediate activities being undertaken
is the development of a guide for the detection
of moisture in concrete and masonry
surfaces. The guide will address the location
and frequency of measurements, the
scheduling of testing within the construction
or maintenance sequence, the instrumentation
that is used, and interpretation
of results.
A common construction trend seen in
many commercial structures is the use of
single-wythe concrete masonry units (CMU),
commonly known as concrete block. It is
extremely important to know the moisture
content in this type of wall system. While
single-wythe CMU provides a relatively economical
wall system, excessive moisture in
these units can cause serious problems for
the performance of the exterior coatings and
can create unfavorable interior conditions.
The creation of an effective drainage plane
can be extremely challenging, depending on
the insulation type and integral structural
components such as bond beams. Various
factors such as solar loading, exterior climate,
interior temperature and humidity
conditions, wind-driven rain, roof system
leaks, and moisture introduced during construction
can all lead to excessive moisture
content in single-wythe wall systems.
Unfortunately, the damaging moisture may
not always be visible on the surface of the
A P R I L 2012 I N T E R FA C E • 2 9
Photo 1 – Moisture in the substrate at the time of application or moisture intrusion months
or years later is destructive to most coating systems.
wall, giving a false sense of assurance that
moisture is not a problem. Excessive moisture
can become trapped within the fill insulation
or accumulate behind the outward
web of the block. Coating the exterior of wall
systems when excessive moisture exists can
lead to unfavorable appearance, patches of
efflorescence, and blistering and peeling of
the coating. If sustained, it can lead to the
decay of materials in contact with the wall
(Photo 2).
A few instruments and
techniques are available for
determining the presence of
moisture in walls, providing
both qualitative and quantitative
results. Unfortunately, the
quantitative methods do not
always measure the same
attributes, the results are in
different units, and the conclusions
that are derived from
the various methods are often
not in agreement. This article
describes some of the methods
that are used for determining
moisture content, available
ASTM standards, and some of
the problems the industry is
facing in interpreting the
Only one ASTM test
method addresses the moisture
content of walls: ASTM
D4263-83 (reapproved in
2005), Standard Test Method
for Indicating Moisture in
Concrete by the Plastic Sheet Method.
In contrast to walls, five ASTM test
methods, in addition to ASTM D4263,
address the measurement of moisture in
floors. Although specifically designed for
floors, some of the methods provide concepts
that can be
of value when evaluating
walls. The
ASTM test methods
for floors are
the following:
• ASTM F1869-11, Standard Test
Method for Measuring Moisture
Vapor Emission Rate of Concrete
Subfloor Using Anhydrous Calcium
• ASTM F2170-11, Standard Test
Method for Determining Relative
Humidity in Concrete Floor Slabs
Using In-Situ Probes
• ASTM F2420-05, reapproved 2011,
Standard Test Method for Determining
Relative Humidity on the Sur –
face of Concrete Floor Slabs Using
Rela tive Humidity Probe Measurement
and Insulated Hood
• ASTM F2659-10, Standard Guide for
Preliminary Evaluation of Com par –
ative Moisture Condition of Concrete,
Gypsum Cement, and Other Floor
Slabs and Screeds Using Non de –
structive Electronic Moisture Meter
• ASTM F710, Standard Practice for
Preparing Concrete Floors to Receive
Resilient Flooring
Various methods that have been used
for determining the moisture content of
walls, although not supported by ASTM
standards (with the exception of ATSM
D4263), are discussed below.
This method is addressed in ASTM
D4263-83 (2005), Standard Test Method for
30 • I N T E R FA C E A P R I L 2012
Photo 2 – Drywall decay attached to insulation that is in
contact with single-wythe masonry.
Photo 4 – Moisture visible beneath plastic.
Photo 3 – Plastic sheet test in place overnight.
Indicating Moisture in Concrete by the Plastic
Sheet Method. This is a nondestructive test
that requires firmly taping the perimeter of
a sheet of plastic (measuring approximately
18 x 18 in.) to the wall and allowing it to
remain in place for a minimum of 16 hours.
At the end of the exposure, the underside of
the sheet and surface of the concrete are
visually examined for the presence of moisture
(see Figures 4 and 5).
The test method recommends a test frequency
of one location per 500 sq. ft. of wall
area or portion thereof, with a minimum of
one test for each 10 ft. of vertical rise in all
elevations starting within 1 ft. of the floor
The use of a good-quality tape and
preparation of the area beneath the tape are
critical on walls. On previously coated surfaces,
loose efflorescence, chalk, and dirt
should be removed and a tape with good
adhesive qualities used; otherwise, the tape
will detach from the surface.
Acceptance criteria are not explicitly
stated in the standard, but coatings are typically
not applied if the test indicates that
moisture is visibly present (see Photos 3 and
4). There can be problems with the reliability
of this method if used in direct sunlight.
Moisture Testing Instruments – Walls
Three categories of commercially available
instruments are discussed below. (The
categories are not based on any standards;
they have been developed for the purpose of
this paper.) While many of the instruments
in the categories below are typically used on
floors, some are also used on CMU, brick,
and concrete walls.
Moisture Meter
Category A,
Radio Frequency
This instrument
utilizes radio
frequency to as –
sess and monitor
the relative moisture
level in po –
rous materials such as concrete. The
instrument from one manufacturer provides
readings on a relative scale between 0
and 999. The instrument displays results
using both a color and a number. The green
zone is from 0 to 145 units and signifies
safe air-dry conditions. The yellow zone is
between 146 and 230 units and signifies
that moisture levels are higher than normal
but not critical; further investigation is recommended.
The red zone is greater than
230 units and represents excessive moisture
levels. The instrument also has the
ability to read through certain coatings and
materials to a nominal depth of ¾ in. The
levels and descriptions are specific to this
manufacturer only and are not based on
industry standards. Photos 5 and 6 show
low and high moisture readings on the mortar
joints of a brick building (green and red
zones respectively). Photo 7 shows the relative
moisture in block behind textured coating.
Moisture Meter Category B, Electrical
Resistance (Conductivity) Meter
This instrument utilizes conductivity to
determine moisture content. Two contact
pins on the end of the instrument are
A P R I L 2012 I N T E R FA C E • 3 1
KTA-Tator, Inc.
Consulting, Testing
and Inspection
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Photo 5 – Low (green) reading on mortar.
Photo 6 – High (red) reading on mortar.
pushed against the test surface to measure
the conductivity of the material between the
pins. One manufacturer recommends driving
masonry nails into the surface about ¼
inch in depth and touching the probe to the
head of the nails (see Photo 8).
Moisture meter B can also be used to
determine the moisture content of insulation
within the wall cavity. (Insulation can
absorb and retain moisture depending on
its cell structure.) Insulated contact pins 4
inches long are inserted through small
holes that are drilled through the face of the
block. The gauge determines the conductivity
of the insulation in contact with the tips
of the pins (Photo 9).
The instruments in Photos 8 and 9 display
a numerical reading that classifies the
relative moisture content in concrete in
three general ranges:
• Green: <85 units (<2% moisture
• Yellow: 85 to 95 units (2% to 4%
moisture content)
• Red: >95 units (>4% moisture content)
Moisture Meter
Classification C,
Impedance Meter
This instrument
utilizes electrical im –
pedance to determine
moisture content. The
electrical impedance
is measured by creating
a low-frequency
alternating electric
field between the electrodes
on the bottom
of the unit. For one of
the manufacturers,
the concrete moisture readings are displayed
on a moving coil meter ranging from
0% to 6%.
Another approach for determining the
presence of moisture is to combine the plastic
sheet test with instrument readings
(before and after installation of the plastic).
Although it is described for use on floors in
ASTM F710, the authors have found the
procedure to provide meaningful results for
Industry acceptance ranges for moisture
content in walls are neither available,
nor is guidance provided for the location
and frequency of measurements. Typically,
specifications only require that the surface
be dry. Basing decisions on visual observations
is risky, as it does not indicate
whether detrimental amounts of moisture
are present beneath the surface. (Photos 5
and 6 of the brick demonstrate how appearance
alone can be misleading for making
decisions regarding moisture.) Unless the
coating manufacturer specifically mandates
moisture testing using instrumentation, it
is often ignored.
32 • I N T E R FA C E A P R I L 2012
Photo 7 – Instrument used on CMU with coating.
Photo 8 – Masonry nails are driven into mortar joints
of CMU to assess the moisture below the surface.
Photo 9 – Conductivity meter with 4-in. probes
inserted into the block cell. Instrument reading
shows that the insulation is wet.
While the ASTM standard for the relative
humidity probes is designed for floors,
there have been instances in which the relative
humidity probes have been used to
examine wall cavities, so even though a
standard does not exist, the technique may
have applications in various wall types. This
method is addressed in ASTM F2170-11,
Standard Test Method for Determining
Relative Humidity in Concrete Floor Slabs
Using In-Situ Probes.
This is a destructive test that requires
drilling holes in the concrete by dry-cut
tooling. The diameter of the holes is not to
be more than 0.04 inches larger than the
diameter of the probe sleeve. The relative
humidity is determined by inserting probes
into the holes after a 72-hour stabilization
period (see Photos 10 and 11).
While infrared has become popular for
detecting moisture in roof systems, it can
also be used to assist in evaluating air leakage
and moisture retention within the wall
system. This method is addressed in ASTM
C1060, Standard Practice for Thermographic
Inspection of Insulation Installations in
A P R I L 2012 I N T E R FA C E • 3 3
Photo 10 – Probe of a relative humidity instrument being inserted into a sleeve that lines a
hole drilled into the surface.
Photos 11A and 11B – Another
relative humidity instrument uses
probes that are inserted into a
sleeve. The relative humidity is
displayed on the top of the reader.
Envelope Cavities of Frame Buildings.
The standard was developed primarily
to detect suspected missing or
inadequate amounts of insulation;
however, it can sometimes be used to
identify areas of excessive moisture.
The use of infrared thermography to
identify moisture in walls can be difficult
to properly perform and interpret.
If done incorrectly or when
weather conditions are not appropriate,
the results can be misleading.
What may appear to be moisture may
actually be missing insulation, air
leakage, or other deficiencies unrelated
to moisture. As with any infrared
scan, skill in interpreting the results is a
Using this method alone is risky, and it
is best utilized in conjunction with other
techniques such as the plastic sheet or the
instruments described above. Photo 12
shows an infrared still shot confirming the
presence of moisture in a single-wythe CMU
block wall.
Determining the saturation levels of
porous materials is sometimes referred to
as the “gold standard” in determining moisture
in walls. However, in order to use this
method on existing structures, some of the
wall components must be removed for
analysis. Measuring the percent saturation
of porous materials when removed from the
wall provides an absolute measurement of
moisture saturation. Some ASTM standards
exist that address measuring moisture content
of porous materials, such as ASTM
C1498, Standard Test Method for Hygro –
scopic Sorption Isotherms of Building Mater –
Although not specifically addressed by a
standard, a more practical and simplified
approach is to remove a unit from a wall
and immediately seal it in plastic. The specimen
should be “double bagged” to reduce
the potential for drying. The sealed specimen
is sent to a laboratory and weighed.
The sample is then placed in a state of ab –
solute saturation with water and weighed.
After absolute saturation, the sample can
then be oven-dried to a constant state and
weighed. By knowing the weights at
34 • I N T E R FA C E A P R I L 2012
Photo 12 – Infrared thermography
used to detect moisture in walls.
Light areas are grouted cells.
Photo 13 – Brick sample removed to
determine percentage of saturation.
Photo 14 – Very high levels of moisture detected behind EPDM on a parapet.
absolute saturation and at a constant
dry state, the percent moisture
saturation as removed from
the structure can be plotted. Photo
13 shows a brick specimen re –
moved from a structure and
bagged for shipment to a laboratory
to measure the percent saturation
of the unit.
The authors have used a radio
frequency device (Photo 14) to nondestructively
determine the relative
moisture content of the substrate
through roofing materials on
low-slope roofs such as single-ply
membranes and built-up roofs.
While the use of the instrument for
this purpose is still under test, the
results to date suggest positive
results when verified with other
methods or techniques to detect
moisture. Most often, this ap –
proach has been used to deter-
A P R I L 2012 I N T E R FA C E • 3 5
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Photo 15 – Elevated moisture identified in the coverboard underneath a built-up roof.
mine the presence of moisture content on
parapet walls when diagnosing the disbonding
of roofing materials or coating failures
on the opposite side.
The same instrument has been used to
nondestructively identify damp or wet
coverboard materials on low-slope roofs.
With its ability to read through most materials
such as coatings and roofing materials,
and its ability to read to depths up to ¾
in., it can help to determine the presence of
wet areas. Photo 15 shows the instrument
being used on a low-slope, built-up roof.
Moisture in porous materials such as
block and concrete is in the form of liquid
water (percent moisture) or water vapor (relative
humidity), with different instruments
or methods available for measuring each.
Unfortunately, the results obtained from
the various instruments and techniques
can be difficult to compare. Even when similar
types of measurements are involved
(e.g., percent moisture), the results between
the instruments are frequently different,
and the methods do not always indicate the
presence of moisture at the same locations
within the substrate. Some assess the
moisture at the surface and some at varying
depths in the substrate.
A comparison between the percent
moisture in a substrate and relative humidity
is shown in Figure 1 for various substrates.
Figure 1 is taken from Moisture in
Concrete and Moisture-Sensitive Finishes
and Coatings, published by Cement
Concrete & Aggregates, Australia (CCAA).
The chart shows that approximately 75%
RH in concrete equates to a moisture content
of approximately 2%. The CCAA also
points out that because of the tiny capillaries
in concrete, a concrete substrate can be
nearly saturated with water and still only
register a moisture content of about 5%.
Accordingly, a relatively low percentage of
moisture in concrete as determined by the
instruments may represent an unacceptable
amount of moisture for painting or
While there are many ASTM standards
that govern the conditioning of floors prior to
moisture testing and test frequencies, similar
guidance is not available for walls.
Likewise, while acceptance criteria have
been developed by manufacturers of floor
coatings and coverings, similar criteria are
typically not available for coatings applied to
walls. The result is that most specifications
fail to address the moisture content of walls.
Several methods for determining moisture
in walls have been discussed; however,
many of these methods were intended for
other purposes and are not addressed in
standards specifically for walls. Important
factors for measuring moisture in walls are
essentially unknown. Factors such as location
of moisture detection within the substrate,
whether standardized test frequencies
are available, and the standardized
acceptance criteria for moisture content in
walls, all require significant development.
On a positive note, one of the goals currently
being addressed by the new SSPC
Commercial Coatings Committee is the
development of a guide that will serve as an
overarching document for the testing of
moisture in walls, with industry standards
referenced when available.
Kenneth A. Trimber is president of KTA-Tator Inc. He is a
National Association of Coating Executives (NACE) Certified
Coatings Inspector Level 3, an SSPC Certified Protective
Coatings Specialist, and is certified at a Level III coating
inspection capability in accordance with ANSI N45.2.6.
Trimber has over 40 years of experience in coatings inspection,
testing, and analysis; is a past president of the Society
for Protective Coatings (SSPC); and is chairman of the SSPC
committees on Surface Preparation, Visual Standards,
Containment, and the newly formed Commercial Coatings
Committee. He is also past chairman of ASTM D1 on Paints and Related Coatings,
Materials, and Applications. He is author of The Industrial Lead Paint Removal
Handbook and coauthor of Volume 2 of the Handbook: Project Design. Trimber was
named Coating Specialist of the Decade at the SSPC National Conference in 1990 and
is also past technical editor of the Journal of Protective Coatings & Linings. He was moderator
of the commercial painting seminar at the SSPC National Conference in February
2011. He has a BS degree from Indiana University of Pennsylvania.
Kenneth A. Trimber
Kevin Brown is the manager of the Commercial Services
Group for KTA-Tator, Inc. In this position, he develops and
implements maintenance programs for commercial clients
nationwide who are experiencing architectural/commercial
problems related to paint failures. Brown has over 12 years of
experience in the field of retail facility management overseeing
building maintenance and preventive maintenance programs
for over 1,700 stores, including store repaints, floor
coating replacements, and long-range budget planning.
Brown holds bachelor’s and master’s degrees in business administration from Gardner-
Webb University. He has been a featured guest speaker at various trade association
conferences, including SSPC, contractor workshops, and lunch-and-learn presentations
for national A/E firms.
Kevin Brown
36 • I N T E R FA C E A P R I L 2012
Figure 1 – Moisture content and relative
humidity comparison chart. Source: Cement
Concrete & Aggregates, Australia