Moisture Intrusion

Moisture Intrusion: The Achilles Heel of Single-Wythe CMU

This is a continuation of the article published in the January/February 2013 issue of Durability + Design, “Repair The Building Before You Repair The Paint.” In that article, a number of building repairs associated with single-wythe concrete masonry units (CMU) were discussed – repairs that should be undertaken before additional coating is applied, including problems with mortar, block, sealants, joints, flashing, wall drainage systems, gutters, and downspouts. But there are even greater issues that need to be evaluated and corrected in order for CMU walls and paint to function as expected. These issues are related to moisture intrusion. The authors have found that moisture intrusion is the leading cause of problems with the performance of paint on both the interior and exterior of single-wythe CMU buildings. The most obvious outward visible signs of moisture intrusion are widespread patches or streaks of efflorescence (Figure 1), the presence of water-filled blisters, peeling of the interior paint, deteriorated drywall (Figure 2), and the presence of mold.

Extensive peeling of the exterior paint may be another indication of moisture problems, although peeling can also occur for reasons unrelated to moisture, such as the quality of surface preparation, incompatibility of products, and the use of a coating that is unsuitable for exterior exposure.

If the building exhibits the problems listed above, simply applying another coat of paint to the exterior will correct the problem in only one instance – when the cause is related to poor wind-driven-rain resistance of the existing finish. Only then will the addition of a new continuous coating correct the moisture intrusion problem. In all other cases, the coating will do nothing to solve the problem. In fact, depending on the cause, it can actually exacerbate the problem, by retaining moisture within the walls. When a building suffers from moisture intrusion, newly applied paint will fail in short order and the energy efficiency of the building can suffer.


While it is easy to recognize that there are moisture problems in a building, the real challenge is in determining, and correcting, the sources of moisture. A comprehensive investigation into the sources of moisture can be a labor-intensive process, requiring two to three days on-site, including evenings or overnights for some of the tests. A complete examination requires the use of many different types of tests in combination. No single test or assessment is capable of providing the answers.

Typical examinations include wall moisture measurements (surface and within the wall cavity); inspection of the roof membrane termination over the parapet and the condition of the capping system; air leakage tests to examine air infiltration/exfiltration at the roof/wall junction and around and above openings such as doors; infrared thermography to detect the presence of insulation, both dry and wet, and air leakage; fiber optics (borescopes) to determine the wall cavity condition; wind-driven rain resistance of the existing coating or waterproofing material; and removal of coating samples for laboratory analysis of coating type, thickness, and condition.

Fig. 1: This photo illustrates obvious signs of moisture problems—efflorescence and staining.
Fig. 2: This is an example of damp, deteriorated drywall under a display rack.

Wall Moisture Measurements

A number of instruments are available for measuring moisture in walls. Detailed information on the use of various moisture meters and test methods can be found in D+D’s January/February 2012 article, “A Hard Assignment: Getting a Good Read on Moisture in Concrete.” The SSPC Commercial Coatings Committee is another good resource for information. The committee has drafted a guide for measuring moisture content in walls, describing the equipment to be used, test locations, and test frequencies. More information on the work of the committee can be found by contacting SSPC or the authors.

For the nondestructive measurement of moisture in the top 1/2-inch to 1-inch of the surface, radio frequency moisture meters (Figure 3) and impedance moisture meters can be used.

Fig. 3: A radio frequency moisture meter measures moisture near the surface. Measurements can also be taken through coatings.

A moisture meter based on conductivity can also be used to measure surface moisture content, but its greatest value is in determining the presence of damp insulation inside the wall cavity, or dampness at the interface between CMU and other directly attached materials such as rigid foam insulation board. By drilling two small holes in the block, probes can be inserted into the cavity (Figure 4), or the probes can be inserted into and through rigid foam insulation board.

Fig. 4: A conductivity instrument is used to determine moisture content within the cavity.

A plastic sheet test, although qualitative, can also be used to detect the presence of moisture in a wall (Figure 5).

Fig. 5: Moisture is visible beneath the plastic after it has been in place for 25 hours.

Using only one of the methods is typically inadequate for reaching conclusions on moisture content. Because the instruments and plastic sheet assess moisture at different locations within the wall, at least three of the methods should be used for an evaluation (one of the instruments for surface moisture measurements, conductivity test for the cavity and interfaces between other materials, as well as the plastic sheet test).

Other methods for assessing the presence of moisture in walls include IR thermography, laboratory testing of building materials (e.g., brick, block, and insulation) for the absolute percentage of saturation, and potentially, relative humidity probes. Each building and situation is different, which will influence the type, extent, and locations of moisture testing that is performed.

Roofing Membrane and Capping Systems

In an examination of the building walls, the roof should be checked for obvious defects such as breaches, standing water, deterioration of the membrane, separating seams, termination of the membrane over the parapet, and the condition of the parapet capping system. Infrared thermography together with simple observations will dictate whether a more detailed roof examination should be scheduled.

For the termination of the membrane, the cap on the outside edge of the parapet normally conceals the membrane material, but sometimes can be pulled back slightly to see or feel whether the membrane wraps over the parapet. The capping system should also be examined for proper sealing at seams and fasteners. While gaps in the seams of the metal cap are not desirable, they do not necessarily create problems with waterproofing if the membrane has been wrapped over the top of the parapet beneath the cap.

Moisture intrusion is a common problem with free standing screen walls. The walls are often installed without a wall cap or waterproofing to keep rain water from saturating the cavity. These walls commonly exhibit significant amounts of efflorescence, peeling paint, and cracking of block or mortar due to moisture intrusion.

Air Leakage Tests

A potential problem with the construction of single-wythe CMU buildings is the lack of a continuous air barrier, especially at the roof/wall junction. Gaps around joist and girder seats and between the roof decking and wall are common (Figure 6). The climate inside and outside of the building and the occurrence of air infiltration/exfiltration at the openings can lead to the condensation of moisture at the top of the walls, potentially saturating the wall cavity or insulation.

Fig. 6: Depending on the interior and exterior climates, air infiltration and exfiltration at openings can lead to the formation of condensation.

Different ASTM test methods and equipment are available to determine and quantify air leakage in buildings. A smoke tracer is one method for determining whether air infiltration or exfiltration is occurring at the openings (Figure 7). The results from the smoke tracer test (or any test method), are influenced by the operation of the mechanical equipment, so the walls must be adequately pressurized prior to testing. Again, different building designs and situations influence the type of testing that is selected, and more importantly, how the information is interpreted.

Fig. 7: A smoke tracer shows interior air being pulled through the gap between the top of the dry-wall and the ceiling. Note the rust staining on the joist, indicating that condensation is occurring.

Infrared Thermography

Infrared (IR) thermography is useful for detecting the presence of insulation, missing reinforcement, excessive moisture, and air leakage. However, the results are often mis-interpreted, yielding little-to-no information. Further, the images can be suspect if there is an insufficient temperature differential between the interior and exterior of the building when the images are created. The authors prefer a minimum 30°F differential whenever possible; this requires scheduling the work during colder seasons and taking the images overnight before dawn.

Figure 8 provides an example of a project where additional tests were required in conjunction with thermography in order to draw conclusions. The blue areas are colder and represent locations of insulation. The vertical and horizontal gold bands represent warmer areas associated with thermal bridging at the grouted cells (structural reinforcing) and bond beams, respectively. The lighter gold above and below the insulation is warmer, which represents either missing insulation or damp insulation. Supplemental tests involving moisture readings (surface and core), and drilling the wall for optical examination with a borescope were used in combination with the thermal images to determine the actual cause of the differences in temperature. In this case, the insulation was missing. The initial installation was very poor.

Figure 9 shows a thermal image of the interior roof of a building, clearly demonstrating the effect that gaps and openings at the roof/wall junction have on air movement. In this case, the facility has a return air plenum. The strong negative pressure created by the units brought cold outside air into the building, lowering the surface temperature of the metal decking. When the surface temperature drops below the dew point of the interior conditioned air, condensation will form on the cold surface, which can also dampen the interior of the walls.

Fig. 8 (left): Blue represents cooler areas where insulation is present. Light brown represents missing or damp insulation. Moisture meters and drilling were used to draw final conclusions.
Fig. 9 (right): Blue shows the effect of colder outside air being drawn into the building at unsealed roof/wall junctions.

Fiber Optics

Fiber optics (borescopes) are used to confirm locations of missing masonry fill insulation and damp insulation, and to visually examine the inside of the cavity walls. Access to the interior surfaces is achieved by drilling a small hole into the wall. For example, a 9 mm cable will fit inside a 3/8-inch hole (Figure 10), and other cable diameters are also available. The cable can be turned to view all interior portions of the wall cavity. A borescope is an excellent complement to thermal imaging and instrument measurements to obtain a more complete analysis of the conditions inside the wall. A borescope is also of value in multi-wythe walls to inspect the condition of internal wall drainage systems and to view the surface behind rain screens.

Fig. 10: In this test, a boroscope is inserted into a 3/8-inch hole to visually examine the inside of the wall cavity.

Wind-Driven Rain Resistance

The coating system itself may be associated with the moisture problems by virtue of insufficient film thickness and coverage, or excessive pinholes. Control joints also contribute to moisture intrusion if they are cracked and separated from the block. In the case of integrally colored block, the waterproofing material may be depleted or non-existent. The effect of these potential deficiencies can be determined by conducting wind-driven rain resistance tests.

There are different ASTM test methods and equipment used to determine wind-driven rain resistance of walls and windows. One such test uses a water spray rack and is similar in principle to the laboratory methods described in ASTM E1105, Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform or Cyclic Static Air Pressure Difference. The authors have had success using a rack constructed of PVC piping fitted with multiple nozzles in order to apply a controlled, uniform stream of water to the surface (Figure 11).

Fig. 11: A water spray rack being used on painted CMU.

Prior to conducting the test, the surface moisture content of the interior and exterior of the wall in the immediate test area is determined. Readings of mortar and grouted cells are included because moisture tends to move more freely through mortar and grout as compared to block.

At the end of the 30-minute test, the interior surface is visually examined for evidence of moisture intrusion (Figure 12). Interior and exterior moisture readings are taken in the same locations as the pre-test readings. This has proven to be a suitable method for determining if the coating or waterproofing is providing adequate protection from wind-driven rain.

Fig. 12: This is an interior wall showing moisture intrusion along grouted cells (right side) and mortar joints after 30 minutes of exterior water rack exposure. The moisture test locations are represented by an “(x).”

Rilem tubes are also used on unpainted masonry to determine whether waterproofing needs to be reapplied.

Laboratory Testing of Samples

In order to do a complete coating analysis, samples can be removed from the walls and analyzed in the laboratory. Many laboratory test methods are available for determining the cause of coating failures and establishing if the existing coating is a candidate for repainting. For example, laboratory analysis may include moisture sensitivity of the film to determine if overcoating is viable; infrared spectroscopic analysis of failing samples to determine the cause, the generic coating type for compatibility, and suitability of the coating for the service environment; microscopic examination for intercoat contamination and dry film thickness of the coating layers (Figure 13); as well as a number of other analytical tests depending on the project-specific conditions and the objectives for the testing.

Fig. 13: Microscopic determination of the thickness of each coat in the cross-section of a coating sample removed from a wall.


Symptoms of moisture problems in a building are easy to recognize – efflorescence, deteriorated drywall, mold, and blistering and peeling coating. When these problems are present, the application of more paint to the walls, without any other repairs, can be a costly mistake. In order for the newly applied coating to perform as expected, the sources of moisture intrusion responsible for the current failure must be first identified and corrected.

Once the causes are established, repair strategies can be specified. Multiple retrofit strategies are often needed on a given building and typically involve more than just paint. Examples include the installation of an air barrier such as expandable closed-cell urethane foam at openings along the tops of the walls and at penetrations; correction of flashing deficiencies, including retro-fitting with new flashing; installation of insulation; tuck pointing; repair of cracks in blocks; replacement of sealants; and overcoating or replacement of the coating with recognition of the permeance of the system. Based on the interior and exterior climates, decisions must be made on whether an “impermeable” coating should be applied on the interior or exterior side of the walls.

Single-wythe buildings are simple to erect, but can be a challenge to maintain once moisture intrusion occurs, especially when core fill insulation becomes saturated. Some of the problems are related to design, and some are related to the quality of construction and painting. The good news is that once the problems are identified, solutions are typically available, although once masonry-fill insulation becomes saturated, it can be difficult, if even possible, to cost-effectively dry. When this occurs, the solutions need to take this into consideration, as the performance of more coats of traditional paint to a wall containing saturated insulation will be short-lived.

KBrownKevin Brown is the Manager of the Commercial Services Group for KTA.  In this position, Kevin develops and implements maintenance programs for commercial clients nationwide who are experiencing architectural/commercial problems related to paint failures.  He has over 12 years of experience in the field of retail facility management overseeing building maintenance and preventative maintenance programs for over 1,700 stores including store repaints, floor coating replacements, and long-range budget planning.


Ken Trimber KTA-TatorKenneth A. Trimber  is the President of KTA-Tator, Inc. and is directly responsible for the overall operation, performance, and success of the company.  Mr. Trimber has been employed by KTA since 1968, where he worked on a part-time basis until his graduation from college in December of 1974.  After graduation, he joined the firm full time.  Mr. Trimber serves as a senior consultant and client liaison on many multi-disciplinary projects as well as a principal specification writer/reviewer. Mr. Trimber is a NACE Certified Coatings Inspector Level 3 (Peer Review) (#362), is an SSPC Certified Protective Coatings Specialist (#339-244-0635).  He has more than 35 years of experience in the industrial painting field, is a Past President of the SSPC, Chairman of the Committee on Surface Preparation, Chairman of the Visual Standards Committee, and Chairman of the Task Group on Containment.  He is also Past Chairman of ASTM D1 on Paints and Related Coatings, Materials, and Applications.  Mr. Trimber authored The Industrial Lead Paint Removal Handbook and co-authored Volume 2 of the Handbook: Project Design.  He has been formally recognized by industry associations/publications on numerous occasions including being named Coatings’ Specialist of the Decade at the SSPC National Conference in 1990 and being selected by the JPCL in 2009 as one of 25 Top Leaders and Thinkers in the Coatings & Linings Industry for the past 25 years.


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