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Flashing Strategies for Concrete Masonry Walls

  • August 2018

INTRODUCTION

The primary role of flashing is to intercept the flow of moisture through masonry and direct it to the exterior of the structure. Due to the abundant sources of moisture and the potentially detrimental effects it can have, the choice of flashing material, and the design and construction of flashing details, can often be as key to the performance of a masonry structure as that of the structural system.

The type of flashing material to be used is governed by both environmental and design/build considerations. Environmental considerations include such factors as the physical state of moisture present (liquid, solid, or vapor), air movement, and temperature extremes as well as temperature differentials. Design/build considerations include the selection of the proper type of flashing material, location of the flashing, structural, and installation details. Drawings for flashing details, often the only method of communicating the necessary information between the designer and contractor, should be comprehensive and show sufficient detail for the proper interpretation and installation of flashing systems. TEK 19-05A Flashing Details for Concrete Masonry Walls (ref. 3) includes such details.

Although flashing is the primary focus of this TEK, it should be understood that the role of vapor retarders, air barriers, and insulation are also important elements to consider for any wall design as the performance of the entire system can be dependent on the design of its individual components.

EFFECT OF MOISTURE ON MASONRY

The damage caused to a masonry structure (or its contents) due to the infiltration of moisture can take many forms, depending on the source and the physical state of the water. For example, in the liquid state, water penetrating to the interior of a building may cause considerable damage to its contents. In some extreme cases, water trapped within the masonry may freeze, inducing spalling and cracking of the masonry units or mortar. Alternatively, water vapor can lead to condensation inside the cores and on the surfaces of masonry if the dew point temperature is reached. During cold weather, below 28 °F (-2 °C), water vapor can accumulate on a cold surface and form frost or increase the quantity of ice within the masonry.

Although it is commonly thought that moisture problems stem only from the external environment, this is not always the case. For example, in some instances it is possible for the humidity of interior air to cause water damage to the exterior of a structure. This damage may appear in the form of water stains, ravelled mortar joints, spalled surfaces, or efflorescence.

DESIGN CONSIDERATIONS

Water Movement

In the design of any structure, the presence and movement of water in any of its three forms needs to be considered. Significant forces that influence water movement include wind pressure, gravity, and moisture absorption by the material. Dynamic wind pressure on the surface of an exposed wall can drive exterior moisture (in the form of rain or irrigation water) into the masonry. Gravity, which is always present, draws the free water vertically downward, while the absorptive characteristics of the masonry can cause moisture migration in any direction by capillary action.

It should also be recognized that these forces do not act independently of one another. For example, wind-driven rain may enter masonry through cracks at the interface between mortar and units and migrate downward through the wall due to the force of gravity, or it may be transferred horizontally through the wall either by pressure or by flowing across the webs of the units or mortar bridges. Wind-driven rain can also be absorbed by masonry units and carried from the exterior surface to the interior surface by capillary action. Additionally, ground water may be drawn upward by the wicking action of units placed on porous foundations or by contact with moist soil.

Designers should never assume that any material is capable of rendering a wall totally impervious to water penetration. Surface treatments, designed to reduce the quantity of water entering a masonry structure, are helpful in this regard but should not be considered as a sole means of protection. Available as clear and opaque compounds, the effectiveness of surface treatments depends on their composition and compatibility with the masonry. They also do not reduce the movement by capillary action (wicking) of any water that does penetrate the masonry face through cracks or defects in the mortar/masonry.

The use of integral water repellent admixtures in concrete masonry units and mortars can also reduce the amount of water entering the masonry. In addition, they inhibit water penetrating the masonry face from wicking to the back face of the wall.

Proper selection and application of surface treatments and integral water repellents can greatly enhance the water resistant properties of masonry, but they should not be considered as substitutes for flashing. See TEKs 19-01 and 19-02B (refs. 8 and 2) for more information on water repellents for concrete masonry.

Flashing Location

The proper design of masonry for resistance to water penetration includes consideration of the various types of wall construction such as single wythe, cavity, veneer, etc. During the design phase it should be understood that all exterior masonry walls may be subjected to some degree of water penetration and/or water vapor movement during its design life. Flashing is recommended for all locations where moisture may potentially penetrate into a wall and where the free drainage of water is blocked. Some of these critical locations include the top of walls and parapets, at all horizontal obstructions such as over openings, beneath sills, above shelf angles, at the base of walls, and in walls at ground level to serve as a moisture retarder to reduce the amount of water wicked up into the masonry above grade.

When selecting the flashing material for a particular application, the service conditions, projected life of the structure, and past performance characteristics of the flashing materials should be reviewed. Flashing should be designed to perform satisfactorily for the design life of the building since repair or replacement can be very labor intensive and expensive.

FLASHING MATERIALS

A wide variety of flashing materials are available. The selection of the type of flashing material to use can be influenced by several factors including cost, durability, compatibility with other materials, ease of installation, aesthetic value, and performance. Table 1 summarizes some of the attributes for various flashing materials. The advantages and disadvantages of each must be weighed for each individual project to provide the most cost-effective and desirable choice.

Prefabricated flashing boots may be available for inside and outside corners and end dams. These boots eliminate the need for cutting, folding, or tucking the flashing materials at these locations. However, due to construction tolerances, some of these prefabricated items, particularly those of rigid materials, may be difficult to fit into their intended location.

Table 1 – Flashing Material Properties (refs. 1, 7)

Sheet Metals

Stainless steel is technically any of a large and complex group of corrosion resistant iron chromium alloys possessing excellent weather and chemical resisting properties. Preformed sections must be properly sized so that on site modification is minimized. Stainless steel flashing with a conventional annealed finish should comply with Standard Specification for Stainless and Heat-Resisting Chromium-Nickel Steel Plate, Sheet, and Strip, ASTM A 167 (ref. 6). Generally, Type 304 stainless steel with a minimum thickness of 0.010 in. (0.25 mm) is satisfactory. Lap sections require solder conforming to Standard Specification for Solder Metal, ASTM B 32 (60% tin and 40% lead) (ref. 5). Stainless steel drip edges used in combination with other flashing materials offer an economical compromise with a durable drip edge.

Copper is a nonferrous metal possessing good ductility and malleability characteristics. Like stainless steel, it also possesses excellent weather and chemical resistant properties. Preformed sections or sheet materials are easily modified to conform to site requirements. However, it should be cautioned that once weathered, copper flashings produce a green patina that may impart a green stain to adjacent masonry surfaces that some find objectionable.

Galvanized steel is less expensive than stainless steel but is subject to corrosive attack from salts and acids. The galvanized coating also may crack at bends, lowering the corrosion resistance. As with stainless steel, it is also difficult to form and to solder laps effectively.

Composites

Combinations of metals and plastics are supplied by some dealers. The composition and application of these combined materials should be determined before use. Composites utilizing copper are the most popular since they combine the durability and malleability of copper with the nonstaining characteristics of a protective coating. Composites containing aluminum should be avoided.

Plastics and Rubber Compounds

Plastics are categorized as polymeric materials of large molecular weight, usually polyvinyl chloride (PVC) or polyethylene. Manufacturers of plastic flashings should be consulted for documentation establishing the longevity of the plastic in a caustic environment (pH = 12.5 to 13.5), the composition of the plastic, ease of working at temperatures ranging from 20 to 100 °F (-7 to 38 °C), and ability to withstand exposure to ultraviolet light.

Ethylene Propylene Diene Monomer (EPDM) is a synthetic rubber that is used as a single ply roofing membrane as well as flashing. It has better low temperature performance than PVC and will not embrittle. It offers ultraviolet light and ozone resistance and can be left exposed.

Self-adhering, rubberized asphalt membranes consist of a composite of flexible plastic film for puncture and tear resistance combined with a rubberized asphalt adhesive layer. This material adheres to itself, requiring less effort to seal laps or corners which speeds installation. It also self-adheres to the substrate which prevents water from migrating under the flashing and is self-healing in the event of punctures. However, it should not be applied to damp, dirty, or dusty surfaces and typically has a lower installation temperature limit of 25 °F (-4 °C). Because it degrades in the presence of extended UV exposure, it should not be left exposed and requires a metal drip edge.

CONSTRUCTION PRACTICES

To perform, flashing must be designed and installed properly or it may aggravate rather than reduce water problems. Flashing should be longitudinally continuous or terminated with end dams. Longitudinally continuous requires that joints be overlapped sufficiently, 4 in. (102 mm) minimum, to prevent moisture from entering between the joints and they must be bonded (joined) together with adhesive if they are not self adhering to prevent water movement through the lap area. With metal flashings a ¼ in. (6.4 mm) gap joined and sealed with a pliable membrane helps in accommodating expansion (ref. 3).

Flashings should be secured at the top by embedment into the masonry, a reglet, or should be adhesively attached so that water cannot infiltrate or move behind the attachment. For multi-wythe construction, the flashing should project downward along the outer surface of the inner wythe and then project outward at the masonry joint, shelf angle, or lintel where it is to discharge the water. Every effort should be made to slope the flashing towards the exterior. Effectively placed mortar or sealant material can help promote this drainage. The flashing should continue beyond the exterior face of the masonry a minimum of ¼ in. (6.4 mm) and terminate with a sloped drip edge.

An additional design consideration for flashings includes ensuring that all materials are compatible. For example, contact between dissimilar metals can result in the corrosion of one or both of the metals. Additionally, the coefficients of thermal expansion for the flashing and masonry materials differ. All flashing details should be designed to accommodate the resulting differential movement.

Other recommended practices involve the use of tooled concave mortar joints to reduce water penetration through the mortar joints. Masons should be careful to ensure that mortar dropped onto the flashing is minimized. This can be accomplished by beveling the mortar on the face shells adjacent to the cavities in cavity wall construction. In addition, cavity drainage mats, gravel beds, screens, or trapezoidal drainage material (filter paper) can be used to prevent mortar droppings from collecting on the flashing, which can form dams and block weep holes. Mortar collection devices at regular intervals or filling the cells with loose fill insulation a few courses at a time as the wall is laid-up, can be effective in dispersing minor mortar droppings enough to prevent clogging.

Weep holes, the inseparable companion to flashings, should provide free movement of water out of the concrete masonry cores, collar joints, or cavities. Any construction practice that allows forming the weep holes without inhibiting water flow may be used. Cotton sash cords and partially open head joints are the most common types of weep holes. Cotton sash cords should be removed prior to putting the wall into service to provide maximum unobstructed drainage. If necessary, insects can be thwarted by inserting stainless steel wool into the openings or using plastic or metal vents.

Vents

Weep holes often serve a dual function, first for water drainage and second as vents. Vents are desirable in some masonry wall systems to help reduce the moisture content of the masonry during drying periods. Air circulation through the cores and cavities within the masonry promotes equalization of moisture content throughout the masonry. Vents are considered desirable where air is confined within masonry, such as in parapets or areas of high humidity such as natatoriums.

MAINTENANCE

Maintenance programs should involve preserving the “as-built” design documents, records pertaining to inspections during the life of the structure, and continuing appraisal of the performance of the structure in addition to conventional repair and upkeep. Documentation of inspections, if efflorescence and water stains are observed, and logs of reported water penetration and their identified location, assist in determining proper corrective actions. Pictures with imprinted dates are suggested.

Knowledge of the wall design and construction can influence repair decisions. If flashing and weep holes were omitted during construction, it may prove effective to simply drill weep holes and vents to promote drainage and drying. Weep holes so drilled should be either at the intersection of the bed and head joints or into the cores at the bottom of the wall. Vents should be installed at the top of the wall or directly below bond beams. See TEK 08-01A Maintenance of Concrete Masonry Walls (ref. 4) for more detailed information on maintenance of concrete masonry walls.

When considering maintenance options, it is important to ensure that a masonry wall’s moisture control measures are kept intact. Thus, applying sealant beads, pargings, or coatings to a wall should be carefully weighed. Weep holes and vents should be maintained in an open condition to allow evacuation of moisture.

SUMMARY

Flashings are essential at foundations, bond beams, above and below openings, at shelf angles and at copings. Weep holes and vents reduce the moisture content of masonry walls. Proper selection of flashing materials, proper detailing, and proper installation will help ensure satisfactory performance.

REFERENCES

  1. The Building Envelope: Solutions to Problems, Proceedings from a national seminar series sponsored by Simpson Gumpertz & Heger Inc., 1993.
  2. Design for Dry Single-Wythe Concrete Masonry Walls, TEK 19-02B, Concrete Masonry & Hardscapes Association, 2012.
  3. Flashing Details for Concrete Masonry Walls, TEK 19-05A, Concrete Masonry & Hardscapes Association, 2008.
  4. Maintenance of Concrete Masonry Walls, TEK 08-01A, Concrete Masonry & Hardscapes Association, 2004.
  5. Standard Specification for Solder Metal, ASTM B 32-04, ASTM International, 2004.
  6. Standard Specification for Stainless and Heat-Resisting Chromium-Nickel Steel Plate, Sheet, and Strip, ASTM A 167-99(2004), ASTM International, 2004.
  7. Through-Wall Flashing, Engineering and Research Digest No. 654, Brick Industry Association.
  8. Water Repellents for Concrete Masonry Walls, TEK 19-01, Concrete Masonry & Hardscapes Association, 2006.

 

Design for Dry Single-Wythe Concrete Masonry Walls

  • August 2018

INTRODUCTION

Single-wythe concrete masonry walls are cost competitive because they provide structural form as well as an attractive and durable architectural facade. However, because they do not have a continuous drainage cavity (as do cavity and veneered walls), they require special attention to moisture penetration.

The major objective in designing dry concrete masonry walls is to keep water from entering or penetrating the wall. In addition to precipitation, moisture can find its way into masonry walls from a number of different sources (see Figure 1). Dry concrete masonry walls are obtained when the design and construction addresses the movement of water into, through, and out of the wall. This includes detailing and protecting building elements including parapets, roofs, all wall penetrations (utility and fire protective openings, fenestration, doors, etc.), movement joints, sills and other features to resist water penetration at these locations. Annotated Design and Construction Details for Concrete Masonry (ref. 1) contains comprehensive details for reinforced and unreinforced concrete masonry walls. Further, condensation and air leakage must be controlled. See the Condensation Control section on page 7.

The primary components of moisture mitigation in concrete masonry walls are flashing and counter flashing, weeps, vents, water repellent admixtures, sealants (including movement joints), post-applied surface treatments, vapor retarders and appropriate crack control measures. For successful mitigation, all of these components should be considered to be used redundantly, however not all will be applicable to all wall systems. For example, flashing and weeps are not necessary in solidly grouted construction, and may not be appropriate in areas of high wind or seismic loading where compromise of masonry shear resistance may occur (see the Wall Drainage section on page 3 for more information). The determination on structural effect must be made by the structural engineer. As another example, the use of integral water repellents for surfaces to receive a stucco finish may not be appropriate. Successful design for moisture mitigation considers each of these components, and provides for redundancy of protection, also known as a “belt and suspenders” approach.

This TEK provides a brief overview of the issues to consider when designing single wythe walls for water penetration resistance. The information presented is not meant to be comprehensive. Where appropriate, references to more detailed sources are provided.

Figure 1—Moisture Sources

SOURCES OF WATER IN WALLS

Driving Rain

Although concrete masonry units and mortar generally do not allow water to pass through quickly, rain can pass through if driven by a significant force. Cracks caused by building movements, or gaps between masonry and adjoining building elements are common points of water entry. If rain enters wall other than by way of the roof or at element interfaces (such as penetrations and window openings), it often can be traced to the masonry unit-mortar interface.

Capillary Action

Untreated masonry materials (without a compatible integral water repellent and/or post-applied surface treatment) typically take on water through absorption, adsorption and/or capillary forces. The amount of water depends on the characteristics of the masonry and mortar. Integral water repellents greatly reduce the absorption and adsorption characteristics of the units and mortar, but may not be able to prevent all moisture migration if there is a significant head pressure of approximately 2 in. water (51 mm) or more. Post-applied surface treatments reduce moisture penetration of masonry at the treated surface as well, but have little effect on the interior of the units.

Water Vapor

Water as vapor moves through a wall either via air leakage or by diffusion (from higher to lower: relative humidity, pressure and/or temperature). As air cools, it becomes more saturated, and when it reaches the dew point temperature the water vapor will condense into liquid form. See the Condensation Control section on page 7 for more information.

Ground Water

Protecting below-grade walls from water entry involves installing a barrier to water and water vapor. Below grade moisture tends to migrate from the damp soil to the drier area inside the basement. An impervious barrier on the exterior wall surface can prevent moisture entry. The barrier is part of a comprehensive system to prevent water penetration, which includes proper wall construction and the installation of drains, gutters, and proper grading (location of finished grade as well as grade sloping away from the building). Landscaping can also contribute to water ponding adjacent to the foundation wall and/or to insufficient drainage. IBC Section 1805 contains requirements for dampproofing and water proofing foundations. More detailed information for concrete masonry foundation walls can be found in Preventing Water Penetration in Below Grade CM Walls, TEK 19-03B (ref. 2).

DESIGN CONSIDERATIONS

When designing for moisture mitigation in walls, three levels of defense should be considered: surface protection (properly constructed mortar joints, surface water repellents, surface coatings), internal protection (integral water repellents), and drainage/drying (flashing, weeps, vents). The most successful designs often provide redundancy among these three levels. This redundant design approach helps ensure that the wall remains free of moisture problems even if one of the defense mechanisms is breached. Flashing and weeps, for example, provide a backup in case surface coatings are not reapplied as needed or leaks develop around windows or other openings. The following sections discuss the individual mechanisms in more detail.

Physical Characteristics of the Units

Open-textured concrete masonry units possessing large voids tend to be more permeable than closed-textured units. The texture can be affected by aggregate gradation, water content of the concrete mix, amount of cement in the mix, other materials in the mix such as admixtures, and the degree of compaction achieved during molding. These factors can also affect capillary action and vapor diffusion characteristics. Units should be aged at least 21 days if possible before installation to reduce the chance of shrinkage cracks at the mortar-unit interface.

Smooth-faced units facilitate mortar joint tooling, so will generally result in a more water resistant wall, as opposed to fluted units which are more difficult to tool and therefore the most susceptible to leakage. Horizontal effects such as corbels and ledges that may hold water are more prone to water penetration.

Integral Water Repellents

The use of integral water repellents in the manufacture of concrete masonry units can greatly reduce the wall’s absorption characteristics. When using units with an integral water repellent, the same manufacturer’s water repellent for mortar must be incorporated in the field for compatibility and similar reduced capillary action characteristics.

Integral water repellents make masonry materials hydrophobic, significantly decreasing their water absorption and wicking characteristics. While these admixtures can limit the amount of water that can pass through units and mortar, they have little impact on moisture entering through cracks and voids in the wall. In addition, when using an integral water repellent, any water that does penetrate can not exit as easily. Therefore, even with the incorporation of integral water repellents, flashing and weeps, as well as proper detailing of control joints and quality workmanship are still essential. See Water Repellents for Concrete Masonry Walls, TEK 19-01 (ref. 3), and Characteristics of CMU with Integral Water Repellent, TEK 19-07 (ref. 4), for more complete information on integral water repellents for concrete masonry walls.

Post-Applied Surface Treatments

For integrally colored architectural masonry, a clear surface treatment should be post-applied whether or not integral water repellent admixtures are used. Most post-applied coatings and surface treatments are compatible with integral water repellents although this should be verified with the product manufacturers before applying. When using standard units for single-wythe walls, application of a clear treatment, portland cement plaster (stucco), paint, or opaque elastomeric coating improves the water resistance of the wall. Coatings containing elastomerics have the advantage of being able to bridge small gaps and TEK 19-02B 3 CONCRETE MASONRY & HARDSCAPES ASSOCIATION masonryandhardscapes.org cracks. See Water Repellents for Concrete Masonry Walls, TEK 19-01 (ref. 3) for more detailed information.

Wall Drainage

In areas with high seismic loads, masonry walls tend to be heavily reinforced and it is often more economical to fully grout the masonry. In fully grouted masonry, flashing is not necessary. In these cases, the wall is designed as a barrier wall, rather than as a drainage wall.

When flashing is used, the importance of proper detailing cannot be over-emphasized. Traditionally, through-wall flashing has been used to direct water away from the inside wall face and toward weep holes for drainage. Figure 2 shows one example of flashing that spans completely across the width of the wall. In this example, the termination angle prevents any water that collects on the flashing from penetrating to the interior, and the weeps and drip edge drain water to the exterior.

Where it is necessary to retain some shear and flexural resistance capabilities, there are several options. One is to terminate the flashing within the inside face shell of the wall, as shown in Figure 3. In reinforced walls, some shear is provided through doweling action of the reinforcement, and by design the reinforcement takes all tension (refs. 5, 6). Proper grouting effectively seals around where the vertical reinforcement penetrates the flashing. The absence of reinforcement to provide doweling in plain masonry may be more of a concern, but loads tend to be relatively low in these applications. If structural adequacy is in doubt, a short reinforcing bar through the flashing with cells grouted directly above and below can be provided as shown in Figure 3c.

A better option to maintain shear at the level of the flashing is to use a product that maintains some bond in both face shells, such as that shown in Figure 4.

Ensuring that a buildup of mortar droppings does not clog the cells or weep holes is critical. Traditionally, a cavity filter consisting of washed pea stone or filter paper immediately above the flashing was provided to facilitate drainage, as shown in Figure 3. This should be accompanied by a means of intercepting or dispersing mortar droppings, as an accumulation can be sufficient to completely fill and block a cell at the bottom. As an alternative, mortar interception or isolation devices that provide pathways for the water to migrate through the layer of mortar droppings, or filling the cells with loose fill insulation a few courses at a time as the wall is laid up, can disperse the droppings enough to prevent clogging. Examples of polyester mesh drainage mats are shown in Figures 4 and 5. Another alternative is to leave out facing block at regular intervals just above the flashing until the wall is built to serve as cleanouts. The units left out can be mortared in later. See Flashing Strategies for Concrete Masonry Walls, TEK 19-04A and Flashing Details for Concrete Masonry Walls, TEK 19-05A, (refs. 7, 8) for an in-depth discussion and additional details regarding flashing.  

In addition to conventional flashing systems, proprietary flashing systems are available that direct the water away from the inside face of the wall to weep holes without compromising the bond at mortar joints in the face shells. See Figure 4 for one example. These are not intended to be comprehensive, but rather to provide examples of some types of available systems. Specialty units that facilitate drainage are also available from some manufacturers.

Solid grouted single-wythe walls do not require flashing because they are not as susceptible to moisture penetration, since voids and cavities where moisture can collect are absent. However, fully cured units and adequate crack control measures are especially important to minimize cracks. In some regions of the country, the bottom of the wall is recessed about 1 in. (25 mm) below the floor level to ensure drainage to the exterior.

Figure 2—Three-Piece Through-Wall Flashing
Figure 3—Flashing Details to Maintain Structural Continuity
Figure 4—Pan Flashing with Integral Weeps
Figure 5—Stainless Steel Strip with Integral Weeps

Crack Control

Because cracks provide an entry point for rainwater and moist air, crack control provisions are very important in producing dry walls. There are various sources of potential wall cracking. A detailed list, as well as an overview of crack control strategies, can be found in Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23 (ref. 9).

Control joints and/or horizontal reinforcement should be located and detailed on the plans to alleviate cracking due to thermal and shrinkage movements of the building. Specifying a quality sealant for the control joints and proper installation is a must to maintain the weather-tightness of the joint. Joint Sealants for Concrete Masonry Walls, TEK 19-06A (ref. 10) contains more comprehensive information on this topic. See Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23 (ref. 11) for detailed information on control joint placement and construction.

Mortar and Mortar Joints

The type of mortar and type of mortar joint can also impact a wall’s watertightness. A good rule of thumb is to select the lowest strength mortar required for structural and durability considerations. Lower strength mortars exhibit better workability and can yield a better weather-resistant seal at the mortar/unit interface. See Mortars for Concrete Masonry, TEK 09-01A (ref. 12), for a more complete discussion.

Unless otherwise specified, mortar joints should be tooled to a concave profile when the mortar is thumbprint hard (refs. 5, 13), as shown in Figure 6. For walls exposed to weather, concave joints improve water penetration resistance by directing water away from the wall surface. In addition, because of the shape of the tool, the mortar is compacted against the concrete masonry unit to seal the joint. V-shaped joints result in sharper shadow lines than concave joints. Raked, flush, struck, beaded, grapevine, squeezed or extruded joints are not recommended in exposed exterior walls as they do not compact the mortar and/or they create ledges that intercept water running down the face of the wall.

Head and bed joints should be the full thickness of the face shells for optimum water resistance. Head joints are particularly vulnerable to inadequate thickness (see Figure 7).

Figure 6—Mortar Joint Profiles
Figure 7—Mortar Joints Should Be the Full Thickness of the Face Shells

Condensation Control

Condensation is a potential moisture source in building assemblies. Because condensation potential varies with environmental conditions, seasonal climate changes, the construction assembly, building type and building usage, condensation control strategies vary as well. For a full discussion, see Condensation Control in Concrete Masonry Walls, TEK 06-17B, and Control of Air Leakage in Concrete Masonry Walls, TEK 06-14A (refs. 14, 15).

Note that the location and vapor permeability of insulation can influence the condensation potential of a wall. The following references provide more detailed information. Insulating Concrete Masonry Walls, TEK 06-11A (ref. 16), discusses various insulation strategies and the advantages and disadvantages of each. R-Values and U-Values for Single Wythe Concrete Masonry Walls, TEK 06-02C, and Thermal Catalog of Concrete Masonry Assemblies (refs. 17, 18) provide calculated thermal values of various walls and insulation types. Details for Half-High Concrete Masonry Units, TEK 05-15 (ref. 19), contains comprehensive details of various single wythe walls.

Cleaning

Concrete masonry cleaning methods can generally be divided into four categories: hand cleaning, water cleaning, abrasive cleaning and chemical cleaning. In general, the least aggressive method that will adequately clean the wall should be used, as overzealous cleaning can damage the water repellent characteristics of the wall. Keeping the masonry wall clean as the construction progresses using a brush and water minimizes cleaning efforts after the mortar has hardened. See Cleaning Concrete Masonry, TEK 08-04A (ref. 20) for more detailed information.

SPECIFICATIONS

Well-worded specifications are essential to ensure the design details are properly constructed. Items to address in the contract documents in addition to those previously mentioned include:

  1. All work to be in accordance with the International Building Code and Specification for Masonry Structures (refs. 5, 13).
  2. Require a qualified mason by documentation of experience with similar type projects.
  3. Require sample panels to assure an understanding of the level of workmanship expected and to be used as a standard of reference until the project is completed.
  4. Proper storage of all masonry materials (including sand) at the job site to protect from contaminants such as dirt, rain and snow.
  5. The tops of unfinished walls shall be covered at the end of each work day. The cover should extend 2 ft (610 mm) down each side of the masonry and be held securely in place.

REFERENCES

  1. Annotated Design and Construction Details for Concrete Masonry, TR 90. National Concrete Masonry Association, 2002.
  2. Preventing Water Penetration in Below-Grade CM Walls, TEK 19-03B, Concrete Masonry & Hardscapes Association, 2012.
  3. Water Repellents for Concrete Masonry Walls, TEK 19-01, Concrete Masonry & Hardscapes Association, 2006.
  4. Characteristics of CMU with Integral Water Repellent, TEK 19-07, Concrete Masonry & Hardscapes Association, 2008.
  5. International Building Code. International Code Council, 2012.
  6. Building Code Requirements for Masonry Structures, TMS 402-11/ACI 530-11/ASCE 5-11, reported by the Masonry Standards Joint Committee, 2011.
  7. Flashing Strategies for Concrete Masonry Walls, TEK 1904A, Concrete Masonry & Hardscapes Association, 2008.
  8. Flashing Details for Concrete Masonry Walls, TEK 19-05A, Concrete Masonry & Hardscapes Association, 2008.
  9. Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23, Concrete Masonry & Hardscapes Association, 2023.
  10. Joint Sealants for Concrete Masonry Walls, TEK 19-06A, Concrete Masonry & Hardscapes Association, 2014.
  11. Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23, Concrete Masonry & Hardscapes Association, 2023.
  12. Mortars for Concrete Masonry, TEK 09-01A, Concrete Masonry & Hardscapes Association, 2004.
  13. Specification for Masonry Structures, TMS 602-11/ACI 530.1-11/ASCE 6-11, reported by the Masonry Standards Joint Committee, 2011.
  14. Condensation Control in Concrete Masonry Walls, TEK 06-17B, Concrete Masonry & Hardscapes Association, 2011.
  15. Control of Air Leakage in Concrete Masonry Walls, TEK 06-14A, Concrete Masonry & Hardscapes Association, 2011.
  16. Insulating Concrete Masonry Walls, TEK 06-11A, Concrete Masonry & Hardscapes Association, 2010.
  17. R-Values and U-Values for Single Wythe Concrete Masonry Walls, TEK 06-2C, Concrete Masonry & Hardscapes Association, 2012.
  18. Thermal Catalog of Concrete Masonry Assemblies, CMU-MAN-004-12, Concrete Masonry & Hardscapes Association, 2012.
  19. Details for Half-High Concrete Masonry Units, TEK 05-15, Concrete Masonry & Hardscapes Association, 2010.
  20. Cleaning Concrete Masonry, TEK 08-04A, Concrete Masonry & Hardscapes Association, 2005.