Frequently Asked Questions

The decision to utilize this information is not within the purview of MIM, and persons making use of this information do so at their own risk. MIM makes no representation or warranties, expressed or implied, with respect to the accuracy or suitability of this information. MIM and its members disclaim liability for damages of any kind, including any special, indirect, incidental, or consequential damages, which may result from the use of this information. This information is not to be interpreted as indicating compliance with, or waiver of, any provision of any applicable building code, ordinance, standard or law.

Materials: Concrete Masonry Unit (CMU)

Yes. ASTM C90 specifies a viewing distance of not less than 20-ft. However, this viewing distance is often misused. The most common ways that the ASTM C90 viewing distance has been misused are:

  1. Viewing the completed wall assembly and not only the CMUs
  2. Viewing CMUs at less than 20-ft
  3. Viewing CMUs under direct lighting, and not diffused lighting. According to ASTM C90, the CMUs are viewed specifically for non-permitted chips, cracks, and other imperfections.

ASTM C90 Section 7.2 states; “Where units are to be used in exposed wall construction, the face or faces that are to be exposed shall not show chips or cracks, not otherwise permitted in 7.1.2 and 7.1.3, or other imperfections when viewed from a distance of not less than 20-ft under diffused lighting.”

NCMA FAQ 11-14 includes the following commentary:

  • Section 7.2 Commentary Discussions

ASTM C90 is a manufacturing standard – addressing the minimum requirements for block. It does not cover design, application, workmanship, etc. – each of which is necessary for the successful application of a C90-compliant concrete masonry unit. It is often interpreted that the 20-foot criterion above applies to the units that are installed. While this requirement could be applied as such, its true intent is for assessing units prior to their installation – again, because this is a product standard. When applying these limits to units that have already been installed, one should note that units may become damaged between the time they were delivered and the time they were installed. This should be taken into consideration. One reason that these requirements are applied to a finished assembly is because there are not standardized means of assessing workmanship or appearance of completed masonry assemblies.

Resources

ASTM Standard C90-16a, “Standard Specification for Loadbearing Concrete Masonry Units,” ASTM International, West Conshohocken, PA, 2016, www.astm.org

National Concrete Masonry Association. (2010, June 9). Commentary Discussions to ASTM C90-09 Standard Specification for Loadbearing Concrete Masonry Units.

No; there is not a standardized means of assessing workmanship or appearance of completed masonry assemblies as noted by NCMA.

TMS 602 does not address a viewing distance for sample panels. TMS 602 Commentary states; “Sample panels should contain the full range of unit and mortar color. Each procedure, including cleaning and application of coatings and sealants, should be demonstrated on the sample panel. Certain elements of sample panels, such as the type of mortar joint, can have structural implications with the performance of masonry. Construct sample panels within the tolerances of Article 3.3F. The specifier has the option of permitting a segment of the masonry construction to serve as a sample panel or requiring a separate stand-alone panel.”

There is a specified viewing distance in ASTM C90 for CMUs (Refer to Is there a recommended viewing distance for concrete masonry units (CMUs) for more information.). The MIM FAQ references NCMA FAQ 11-14. The NCMA FAQ points out that there is not a standardized means of assessing workmanship or appearance of completed masonry assemblies. The NCMA FAQ also states; “It is often interpreted that the 20-foot criterion above applies to units that are installed. While this requirement could be applied as such, its true intent is for assessing units prior to their installation – again, because this is a product standard.” Based on this commentary discussion and since the industry has accepted the 20-foot rule for viewing the units, the MIM Generic Wall Design Committee recommends that it be applied to viewing the completed wall assembly.

Below are some suggestions for viewing CMU sample panels or viewing CMU walls at completion:

  1. View the CMU sample panel or completed wall at a distance not less than 20-feet
  2. View the CMU sample panel or completed wall under diffused lighting. Note that this is especially critical for walls exposed on both sides (i.e., interior hallway).
  3. Note the viewing time:
    1. At delivery (consider this when the viewing distance will be less than 20 feet)
    2. At installation (consider this when the viewing distance can be 20 feet)
  4. Compare the wall assembly to established criteria1:
    1. For the units, ASTM C90 provides requirements for non-permitted chips, cracks, or other imperfections.
    2. For the mortar, from PCA Masonry Walls and the Importance of Mockups
      1. Initial agreement between the owner or their representative and the contractor or mason on what constitutes desired appearance
      2. An understanding by both of the inherent limitations of the system
  • Careful control of influencing variables by the contractor and mason

Footnotes:

  1. MIM recommends that acceptance criteria be established at the preconstruction meeting so that all parties agree. MIM has developed a preconstruction agenda available on their website, masonryinfo.org

Resources

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

ASTM Standard C90-16a, “Standard Specification for Loadbearing Concrete Masonry Units,” ASTM International, West Conshohocken, PA, 2016, www.astm.org

National Concrete Masonry Association. (2010, June 9). Commentary Discussions to ASTM C90-09 Standard Specification for Loadbearing Concrete Masonry Units. https://ncma.org/resource/faq-11-14/

Portland Cement Association. (n.d.). Masonry Walls and the Importance of Mockups.

Typically, Concrete Product Producers manufacture their CMUs using locally available aggregates. These aggregates, when mixed with cement and water, produce specific block physical properties which are inherent with the locally available aggregates.

Relative to the manufacture of CMUs, Michigan’s normal weight aggregates of sand, gravel, and limestone (ASTM C33) are abundant throughout the state. When these predominant aggregates are utilized in the CMU manufacturing process, the resulting CMUs are most nearly classified by ASTM as normal weight (density of 125 lb/ft3 and above).

Historically, expanded slag, a lightweight aggregate (ASTM C331), has been available in southeast Michigan which offered Concrete Product Producers the option of blending the expanded slag with normal weight aggregates to produce a medium weight CMU (density greater than or equal to 105 lb/ft3 and less than 125 lb/ft3). Compared with normal weight units, medium weight units offer the mason contractor a lighter weight unit and offer the designer potentially increased fire ratings and reduced coefficients of thermal expansion. These benefits were realized for a reasonably priced premium when compared to normal weight units.

More recently, some Michigan Concrete Product Producers have chosen to inventory only normal weight units, some have inventoried both normal weight and medium weight units, and some have chosen to inventory only medium weight units. In southeast Michigan, a medium weight unit came to be known as the “standard” unit that is inventoried in most Concrete Product Producers’ yards.

In today’s market, expanded slag has virtually become unavailable to southeast Michigan producers unless trucking the aggregate in from neighboring states or even Ontario, Canada. As a result, there is a premium for medium weight CMUs compared to normal weight CMUs in these markets. Most manufacturers in these markets do not feel as thought he market in this region will bear this premium. Given this premium, many manufacturers have either changed or are in the process of changing their inventory to normal weight units. Medium weight units will still be available in the southeast Michigan, but on a much more limited basis than in the past and at a premium. Outside of the southeast Michigan market, medium weight and light weight CMUs are more readily available.

ASTM C90 contains a footnote which states, “When particular features are desired such as surface textures for appearance or bond, finish, color, or particular properties such as density classification, higher compressive strength, fire resistance, thermal performance or acoustical performance, these features should be specified separately by the purchaser. Suppliers should be consulted as to the availability of units having the desired features.”

To assist the designer and specifier when features are desired, the following are suggested guidelines:

  1. CMUs should be specified to meet ASTM C90
  2. All three density classifications (normal weight, medium weight, and light weight) must meet a minimum net area compressive strength of 2000 psi, as stated in ASTM C90. Depending on the mortar type, the compressive strength of the wall increases with higher density CMUs.1
  3. Based on the calculation procedure, the sound transmission class (STC) increases with higher density walls. Codes typically require a STC of not less than 50.2
  4. When designing for moisture management and mitigation in single wythe CMU walls, three levels of defense should be considered3:
    1. Surface protection (properly constructed mortar joints, surface water repellents, surface coatings)
    2. Internal protection (integral water repellents)
    3. Drainage/drying (flashing, weeps, vents)
  5. The coefficient of thermal expansion of CMUs depends to some degree on the density and on the type of aggregate used. Normal weight units have an expansion coefficient of approximately 5×10-6/°F and the value for light weight units is approximately 4×10-6/° The value presented in the TMS 402 is 4.5×10-6/°F.
  6. As the density of the unit increases, the unit’s weight increases. This may affect mason contractor productivity numbers on the job site.
  7. Relative to fire resistance ratings, in general, lower density walls provide more fire resistance.4
  8. Relative to thermal resistance, lower density walls provide higher R-values.5
  9. The heat capacity (thermal mass) increases with higher density walls.5
  10. Relative to structural concerns, increased weight helps with resisting lateral wind load but increases seismic lateral loading.
  11. In the southeast Michigan markets, specifying medium weight or light weight CMUs may affect LEED credits since the materials are not locally sourced.

Footnotes

  1. NCMA has developed a “Unit Strength Calculator” to determine the specified compressive strength of masonry (f’m) based on the unit compressive strength. This tool is available for free through NCMA (ncma.org) or through MIM (masonryinfo.org)
  2. NCMA has developed TEK 13-02A Noise Control with Concrete Masonry. In addition, MIM has a free tool to determine the STC and NRC of wall assemblies.
  3. MIM has developed generic sections and details that are available on their website which incorporate these recommendations.
  4. MIM has developed a guide for determine the most economical wall assembly to achieve a specified fire resistance rating that is available on their website.
  5. MIM has developed a guide for determining the most economical single wythe wall assembly to meet energy code requirements and has an accredited webinar discussing this topic.

Resources

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

ASTM Standard C90-16a, “Standard Specification for Loadbearing Concrete Masonry Units,” ASTM International, West Conshohocken, PA, 2016,

Materials: Grout

TMS 602 Article 1.6E (Grout Demonstration Panel) requires a grout demonstration panel if the applicable requirements of Article 3.5C (Grout Pour Height), Article 3.5D (Grout Lift Height), and 3.5E (Consolidation) are not met. According to TMS 602 Article 3.5G, alternate grout procedures (those that differ from TMS 602 Articles 3.5C, 3.5D, and 3.5E) may be employed when the grout demonstration panel is accepted by the Architect/Engineer. The requirements for cleanouts are given in TMS 602 Article 3.2F and are, therefore, independent of the requirements that may be waived through an accepted grout demonstration panel.

Consequently, a grout demonstration panel cannot be relied upon by the Architect/Engineer to eliminate the need for cleanouts when the grout pour heights exceed 5’-4”. The only recourse for a contractor who wants to avoid cleanouts and still construct masonry to a pour height that exceeds 5’-4” is to obtain approval of the building official for a “special system of construction”, as permitted by TMS 402 Section 1.3 (Alternative design or method of construction) or IBC Section 104.11 (Alternative materials, design and methods of construction and equipment).

Resources

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

International Code Council (2018). International Building Code, 2018. International Code Council.

International Code Council (2015). International Building Code, 2015. International Code Council.

The masonry code and specification referenced by IBC 2018 is the TMS 402/602-16 Building Code Requirements and Specification for Masonry Structures.  TMS 602 Specification, Article 3.5 D. addresses grout lift heights. 

There are basically four types of grouting (see Table 1):

  1. Grouting with no cure time limit
  2. Conventional grout with no intermediate bond beams
  3. Conventional grout with intermediate bond beams
  4. Self-consolidating grout with or without intermediate bond beams.

There are two terms that need to be defined: “grout lift” and “grout pour”.

  • Grout pour is the total height of masonry to be grouted prior to erection of additional masonry. A grout pour consists of one or more grout lifts.
  • Grout lift is an increment of grout height within a total grout pour. A grout pour consists of one or more grout lifts.

Resources:

TMS 402/602-16 Building Code Requirements and Specification for Masonry Structures

Materials: Mortar

Glazed masonry units are a good choice for clean room walls because the glazed surface is relatively easy to clean. Furthermore, glazed units (such as those complying with ASTM C744 or ASTM C126) are fabricated to be placed with 1/4-inch wide mortar joints while non-glazed units (such as those complying with ASTM C90 or ASTM C212) are fabricated to be placed with 3/8-inch wide joints. Narrower joints are preferred in clean room applications because mortar is not as easy to clean as the glazed surface. Larger masonry units, such as glazed concrete block or glazed hollow clay tile, are preferred to smaller masonry units, such as glazed brick, because the constructed wall has fewer mortar joints.

For mortar used with glazed concrete masonry units, the Portland Cement Association1 recommends adding a water repellent admixture to the mortar to reduce absorption of the constructed mortar joints.

To improve resistance to biological growth, a mildewcide or fungicide that has been proven to be not detrimental to mortar properties may be added to the mortar that is used to set the glazed units. Another option is to rake back the mortar joints after setting the units, and then point with a proprietary epoxy grout that is specifically formulated for this application.

Footnotes:

  1. This recommendation was provided by Jamie Farny, Market Manager for the Portland Cement Association

Resources:

ASTM Standard C90-16a, “Standard Specification for Loadbearing Concrete Masonry Units,” ASTM International, West Conshohocken, PA, 2016, www.astm.org

ASTM Standard C126-15, “Standard Specification for Ceramic Glazed Structural Clay Facing Tile, Facing Brick, and Solid Masonry Units,” ASTM International, West Conshohocken, PA, 2015, www.astm.org

ASTM Standard C212-14, “Standard Specification for Structural Clay Facing Tile,” ASTM International, West Conshohocken, PA, 2014, www.astm.org

ASTM Standard C744-16, “Standard Specification for Prefaced Concrete and Calcium Silicate Masonry Units,” ASTM International, West Conshohocken, PA, 2016, www.astm.org

ASTM C270 defines two approached for specifying mortar:

  1. The Proportion Method
  2. The Property Method

The Proportion Method is the simpler approach and is used on most projects. The Proportion Method specifies mortar by giving a “recipe” and this method does not require mortar testing (Refer to When should mortar cube testing be performed? for more information). The Proportion Method “recipe” specifies relative quantities of sand and cementitious materials, each measured by volume, to mix and create the appropriate mortar type (Refer to How do I determine what mortar type to specify? for more information).

The Property Method requires mortar testing by a qualified laboratory. A laboratory-prepared mixture is tested to confirm that the physical properties, compressive strength, air content, and water-retentivity meet the requirements of ASTM C270. The laboratory then defines the mixture for mixing mortar in the field.

Note that regardless of whether the Proportion Method or Property Method of specifying mortar is used, the quantity of water in field-mixed mortar is not limited by ASTM C270. ASTM C270 identifies the Proportion Method as the default, so when a specifier does not specify the method of mortar specification, the Proportion Method governs.

Resources:

ASTM Standard C270-14a, “Standard Specification for Mortar for Unit Masonry,” ASTM International, West Conshohocken, PA, 2014, www.astm.org

For new construction, ASTM C270 defines three (3) mortar types: N, S, and M; listed from lower to higher compressive strengths. Within the masonry industry, it is widely accepted to use Type N mortar for new construction unless there is a structural or durability reason to use a higher strength mortar. For veneer, Type N mortar will often be the best choice. Higher compressive strength mortar may be required for structural masonry, below-grade masonry, or masonry in higher seismic regions.

In its non-mandatory appendices, ASTM C270 offers additional guidance on selecting the appropriate mortar type for every project. Appendix X.1 relates the type of structural member and its location (above or below grade) to the preferred mortar type.

Resources:

ASTM Standard C270-14a, “Standard Specification for Mortar for Unit Masonry,” ASTM International, West Conshohocken, PA, 2014, www.astm.org

Mortar is typically specified using the Proportion Method, which is the default in ASTM C270. The only circumstance in which mortar cube testing is required is when the mortar has been specified by the Property Method and the proposed mix design must be verified to meet the requirements of ASTM C270. In that circumstance, the proposed mortar mixture is batched in the qualified laboratory using the laboratory proportions and conditions defined within ASTM C270. Laboratory-prepared mortars differ from field-mixed mortars in the type of sand, the water content (which is less), the curing temperature, and the humidity of the curing environment. Once the qualified laboratory establishes a mix design that satisfies the Property Method of ASTM C270, the qualified laboratory defines the mortar’s component materials and their proportions for the contractor to batch in the field. An appropriate quality assurance measure for field-mixed mortars is inspection during batching and mixing. If test reports are required for compliance, mortar aggregate ratio testing in accordance with ASTM C780 should be considered. The scope of ASTM C270 does not include determination of mortar strength through field testing.

Many designers incorrectly assume that mortar compressive strength testing during the project is a good approach. However, mortar cube testing is of little value for several reasons:

  1. Mortar compressive strength determined by testing a 2-inch cube does not represent mortar compressive strength in the wall assembly where the mortar is typically 3/8-inch thick. Furthermore, mortar cubes are made in non-absorptive molds while mortar used to erect masonry is subject to water absorption from the mortar into the masonry units. Mortar in the wall assembly, with its lower water content (due to absorption), will have greater compressive strength than that in the molded cube formed from the same batch.
  2. Mortar compressive strength testing takes 28 days. If there truly is a problem with the mortar, a significant amount of masonry will have been erected in those 28 days. Mortar aggregate ratio testing in accordance with ASTM C780 can be completed in a half-day.
  3. Compressive strength testing of field-mixed mortar yields inconsistent results because the water content in the mortar will vary with weather conditions. During hot dry weather, the mason contractor will mix the mortar with more water to compensate for evaporation.
  4. The contribution of mortar compressive strength to compressive strength of the wall assembly is small. The masonry units are the greatest factor in assembly compressive strength (Refer to Is the compressive strength of mortar important? for more information).

For these reasons, compressive strength testing of field-mixed mortars does not provide meaningful results.

Resources:

ASTM Standard C270-14a, “Standard Specification for Mortar for Unit Masonry,” ASTM International, West Conshohocken, PA, 2014, www.astm.org

ASTM Standard C780-17, “Standard Test Method for Preconstruction and Construction Evaluation of Mortars for Plain and Reinforced Unit Masonry,” ASTM International, West Conshohocken, PA, 2017, www.astm.org

In loadbearing masonry, mortar compressive strength may have some importance, but mortar only contributes a small amount to the net area compressive strength of masonry (f’m). For ASTM C90 concrete masonry units (CMUs) with a compressive strength of 2000 psi, the net area compressive strength of masonry (f’m) only increases by 250 psi when the mortar is changed from Type N to Type S. The compressive strength of the masonry units is the largest factory, by far, in the net area compressive strength of masonry.

In masonry veneer, mortar compressive strength is not important. The veneer only has to support its self-weight, which results in an axial compressive stress of approximately 10 psi for a 10-ft tall veneer. For ASTM C216 face brick placed in Type N mortar, the assembly compressive strength is at least 1220 psi (for clay brick units with 3000 psi compressive strength). For ASTM C1634 concrete face brick placed in Type N mortar, the assembly compressive strength is at least 2280 psi (for 4-inch tall concrete brick units with 3500 psi compressive strength. Thus, the veneer compressive capacity far exceeds the actual compressive stress to which the veneer is subjected, even with Type N mortar.

Bond is the most important property of hardened mortar and workability is the most important property of plastic mortar. Bond has three facets: strength, extent, and durability. Bond strength affects the ability of the masonry to resist cracking and bond extent affects the ability of the masonry to minimize penetration of water. The tensile and compressive strengths of mortar far exceed the bond strength between the mortar and the masonry units. This is the reason that when cracking occurs, it usually appears at the interface of the units and the mortar. There are many variables that affect development of bond between mortar and units, but workability is one of the most significant factors.

Mortar having good workability can be picked up on a trowel, adhere to the trowel as the mortar is evenly spread on the units, and adheres to the masonry units as they are placed in the wall. Workable mortar supports the weight of masonry units when they are placed and facilitates alignment. As stated in Appendix X1 of ASTM C270, “Good workability is essential for maximum bond with masonry units,” and “Complete and intimate contact between mortar and masonry unit is essential for good bond.”

Good workability affords the mason the best opportunity to achieve “complete and intimate contact”, which is essential for achieving good extent of bond. Workability is affected by the component materials in the mortar. Water improved workability, to an extent, and the mason is permitted to add as much water to the mortar as the mason feels is appropriate. The mason knows that adding too much water makes the mortar unusable to support the weight of masonry units as they are laid and, therefore, makes the mortar unworkable. In Portland cement/lime mortar, the lime gives the mortar its workability. In masonry cement mortar and mortar cement mortar, plasticizing materials and air entrainment give the mortar its workability. High air entrainment reduces bond strength, however, which is reflected in the reduced allowable flexural tensile stress (modulus of rupture strength) values in TMS 402 for masonry cement mortar and air-entrained Portland cement/lime mortar in unreinforced masonry.

In summary, there is usually too much focus on mortar compressive strength and not enough on workability. In ASTM C270, the Proportion Method is the default specification for mortar and is most used. When mortar is specified using the Proportion Method, testing to evaluate mortar compressive strength is not required and is not recommended (Refer to When should mortar cube testing be performed? for more information). Decades of experience have demonstrated that mortars mixed according to ASTM C270 perform appropriately, whether they are specified by the Proportion Method or the Property Method.

Resources:

ASTM Standard C270-14a, “Standard Specification for Mortar for Unit Masonry,” ASTM International, West Conshohocken, PA, 2014, www.astm.org

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Reinforcement

Steel reinforcement in masonry is protected from corrosion by one or more construction practices; cover by cementitious materials (mortar or grout) and/or by application of a corrosion-resistant coating. The protective coating can be mill galvanizing, hot-dip galvanizing, epoxy, or, alternatively, use of stainless steel instead of carbon steel. Steel joint reinforcement is required by TMS 402/602 to be protected by both construction practices (cover and coating). The type and thickness of corrosion-resistant coating depends on whether the masonry is exposed to weather or high humidity (such as in natatoria).

Although TMS 402/602 permits steel reinforcing bars to be galvanized or epoxy-coated, TMS 402/602 does not require a corrosion-resistance protective coating. This is because the depth of masonry cover (combination of grout, mortar, and masonry units) is much larger than the mortar cover over joint reinforcement. Masonry cover over steel reinforcing bars provides sufficient corrosion protection without the need for a protective coating.

According to NCMA TEK 12-4D, “A minimum amount of masonry cover over reinforcing bars is required to protect against steel corrosion…These requirements also help minimize corrosion by providing for a minimum amount of masonry and grout cover around reinforcing bars…”

The other reason why corrosion-resistant coatings are not required and are not commonly used on masonry reinforcement is because masonry is primarily constructed in vertical planes. Conversely, concrete slabs-on-grade, where deicing salts are routinely applied, are subject to chloride intrusion and accelerated corrosion of embedded steel. Steel reinforcement in these members is routinely protected by a corrosion-resistant coating, in addition to being placed with a larger amount of concrete cover. Masonry is not typically exposed to salts in this way.

Epoxy coating is another protective coating that is commonly used in concrete members that are exposed to deicing salts. Although epoxy coating is also permitted by TMS 402/602, bars with epoxy coating are required to have a longer lap length than those without that coating due to the reduced bond development. Epoxy coating results in additional cost and difficulty in construction, which are not justified by substantive improvement in masonry performance because masonry is not exposed to conditions that would warrant that level of protection.

Resources:

National Concrete Masonry Association. (2006). TEK 12-04D Steel Reinforcement for Concrete Masonry. https://ncma.org/resource/steel-reinforcement-for-concrete-masonry/

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

The tolerance for mortar bed joint thickness specified in the TMS 602 is plus or minus 1/8-inch from the specified dimension. In standard modular construction, the default specified bed joint thickness is 3/8-inch. Therefore, a standard mortar bed joint can be placed with a minimum 1/4-inch thickness.

Placing 3/16-inch joint reinforcement wire on the top surface of the concrete masonry units (CMUs) would, theoretically, leave 1/16-inch of top mortar coverage above the wire. However, no top mortar coverage may result when construction tolerances and TMS 402/602 corrosion protection for the joint reinforcement are considered as follows:

  1. Two (2) or three (3) mil thickness of galvanizing increases the wire diameter by four (4) to six (6) mils.
  2. The as-manufactured top and bottom surfaces of a CMU can vary due to texture.
  3. The top surface of CMU courses is required by TMS 602 to be placed true-to-a-line, but the permitted tolerance for true-to-a-line is plus or minus 1/4-inch in 10-feet.
  4. The height of individual CMUs can vary by plus or minus 1/8-inch (per ASTM C90) from the specified height, resulting in potential offsets in the bottom of the CMU course above the joint reinforcement.
  5. A 10-foot length of horizontal joint reinforcement will have some curvature.

Heavy duty (3/16-inch) joint reinforcement can, theoretically, be placed in a 3/8-inch joint. However, limiting such heavy duty joint reinforcement to construction in which the specified mortar bed joint thickness is 1/2-inch or more should be considered to accommodate the tolerances described above.

According to Selecting the Right Joint Reinforcement for the Job, “One compelling reason to use 9 gauge joint reinforcement is for fit and constructability. While the code allows joint reinforcement to have a diameter one half the mortar joint width, the tolerances allowed for units, joints, and the wire itself can hinder the placement of large diameter reinforcement. Use it only when there is no other choice.”

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Joint Reinforcement: Less is More. (July 2015). Masonry Magazine, 44-50.

https://www.masonrymagazine.com/blog/2015/06/24/joint-reinforcement-less-is-more/

Selecting Joint Reinforcement. (June 2014). The Construction Specifier Magazine, 50-58.

https://www.constructionspecifier.com/selecting-joint-reinforcement/

Selecting the Right Joint Reinforcement for the Job. (January 1995). Masonry Construction Magazine, 8-14.

Yes, straight lengths of horizontal joint reinforcement can be field-fabricated to form a continuous corner as follows:

  1. Cut one longitudinal wire,
  2. Bend the other longitudinal wire to for a 90-degree angle,
  3. Bend the cut ends of the longitudinal wire 90-degrees to lap the other cut sections of the longitudinal wire to form the required minimum 6-inch lap splice.

The figure below depicts a 90-degree outside corner of joint reinforcement that has been field fabricated with he required lap splice. The same configuration can be used at an inside corner.

Prefabricated joint reinforcement corners are available from joint reinforcement manufacturers, but field-formed corners have some advantages over prefabricated corners:

  • No extra lead time needed for ordering
  • No additional cost to purchase
  • More likely to be installed because the material is available on the project site
  • Can be custom cut to length and lapped per course, when building a corner lead (racking back)

The TMS 602 does not include a requirement for continuity of horizontal joint reinforcement at corners and, therefore, does not address how to achieve continuity at corners. Nevertheless, constructing joint reinforcement with continuity at corners is good practice and reduces the potential for shrinkage cracking at wall corners.

According to Dr. Thomas J. Langill, Technical Director, American Galvanizers Association, susceptibility to corrosion at the bend, due to potential damage to the zinc galvanizing, is not a concern. “In the case of bending the wire the usual thickness of galvanized coating on the wire makes the potential of coating cracking or crazing during bending very low. Even small cracks in the coating t the bend will not affect the corrosion performance.”

Resources:

Joint Reinforcement: Less is More. (July 2015). Masonry Magazine, 44-50.

https://www.masonrymagazine.com/blog/2015/06/24/joint-reinforcement-less-is-more/

Selecting Joint Reinforcement. (June 2014). The Construction Specifier Magazine, 50-58.

https://www.constructionspecifier.com/selecting-joint-reinforcement/

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

No, neither the TMS 402/602 nor the Michigan Building Code require rebar positioners.

The Michigan Building Code references the TMS 402/602. Neither the TMS 402 nor the TMS 602 require rebar positioners or tying of reinforcing bars.

The commentary to TMS 402 Section 6.1.3 states, “Reinforcing bar positioners are available to control bar position.” However, the corresponding Code section does not require use of such positioners. Figure SC-11 in TMS 602 illustrates typical reinforcing bar positioners, but Article 3.4.B.1 merely states, “Support reinforcement to prevent displacement caused by construction loads or by placement of grout or mortar, beyond the allowable tolerances” without requiring use of positioners. The TMS Masonry Designers Guide (MDG), which is prepared to help users apply the provisions of TMS 402/602, confirms this. In Section 4.2.2.3 (Reinforcing Bars), MDG states, “However, TMS 602 does not require the use of positioners, nor does it specify a maximum spacing for them.”

Although reinforcing bars are not prohibited from being tied, neither the TMS 402 nor the TMS 602 require tying of reinforcement. In fact, both the TMS 402 and the TMS 602 specifically permit reinforcing bars to be lap spliced while not in contact. The MIA Inspector’s Handbook, which was developed as a guide for reinforced hollow unit concrete masonry construction, states in Section 5.7 (Lap Splices, Reinforcing Bars), “Physical tying, or contact, is not a requirement for transferring stresses, however, a designer may require tying of reinforcing bars in the project specifications.”

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

International Code Council (2018). International Building Code, 2018. International Code Council.

International Code Council (2015). International Building Code, 2015. International Code Council.

Society, The Masonry. (2016). The Masonry Society’s Masonry Designers’ Guide, 2016. The Masonry Society.

Masonry Institute of America (2015). Reinforced Concrete Masonry Construction Inspector’s Handbook, 9th Edition. Masonry Institute of America.

Design: Flashing; and Air, Moisture, and Vapor Barriers

Masonry that extends below grade is in a potentially moist environment, so this design feature is not recommended. When the veneer is designed to extend below grade, cells and cavities below the flashing should be filled solidly with mortar and/or grout. With that in mind, four ways to terminate the horizontal leg of base flashing, including their advantages and disadvantages, are discussed below:

  1. Sheet metal drip, hemmed and bent to 45-degrees or 90-degrees: A sheet metal drip, bent to 45-degrees with sealant below the drip, is the detail most frequently recommended by industry organizations because it sheds water from the face of the wall below. However, exposed sheet metal edges (particularly at outside corners and laps) are sharp and pose a risk of injury to people who might be close to the building wall.1 Also, some people object to the aesthetics of exposed sheet metal. Coating the metal with a color that matches the masonry units can overcome this shortcoming.
  2. Sheet metal edge, hemmed and bent 180-degrees: The bend of the sheet metal should be placed at the outside surface of the masonry. The sheet metal should be fully bedded in non-asphaltic mastic or adhesive or non-skinning butyl sealant. This detail does not shed water away from the wall surface below. This detail reduces the appearance of the sheet metal to a thin “line”.2
  3. Flexible flashing cut flush with the outside surface of masonry: This detail minimized the outside appearance of the flashing. When this detail is desired, the flashing should be placed so that it protrudes from the face of wall and should be cut flush. When asphaltic flashing is used, this detail may result in unsightly black drippings. With this detail, non-self-adhesive flashing should be fully bedded in non-asphaltic mastic, adhesive, or non-skinning butyl sealant to prevent water entry below the flashing. Some flashing materials cannot achieve perfect flatness and a wavy line may be visible at the outside surface.3
  4. Flashing recessed 1/2-inch from the outside face of masonry: The advantage to this detail is that the flashing is not visible from the exterior. Also, when asphaltic flashing is used, this detail is not likely to result in unsightly black drippings. Non-self-adhesive flashings should be fully bedded in mastic or adhesive or non-skinning butyl sealant to prevent water movement below the flashing. However, when the flashing is placed recessed from the outside surface, there is risk that the flashing will be drawn into the wall by the weight of mortar droppings, resulting in the outside edge being recessed enough to expose the solidly filled masonry cores below. Most importantly, though, is that this detail is not allowed by the IBC. Consequently, this detail requires building official approval in accordance with IBC Section 104.11 (Alternative materials, design and methods of construction and equipment).

Resources:

International Code Council (2018). International Building Code, 2018. International Code Council.

International Code Council (2015). International Building Code, 2015. International Code Council.

Aesthetics versus Function (April 2016). The Construction Specifier Magazine, 12-24

https://www.constructionspecifier.com/publications/de/201604/index.html

In accordance with the International Building Code 2018:

Section 1402.2 Weather Protection, states; “…The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1403.2, and a means for draining water that enters the assembly to the exterior…

Exceptions:

  1. A weather-resistant exterior wall envelope shall not be required over concrete or masonry walls designed in accordance with Chapters 19 and 21, respectively.”

With respect to this specific FAQ, the IBC minimum requirements, from Section 1402.2 and stated above, include an exception that a weather-resistant exterior wall envelope is not required over masonry (or concrete walls). Typically, MIM has experienced architects detailing a masonry cavity wall the same as a frame wall when it comes to the four control layers (moisture, air, vapor, and thermal). The IBC does not require moisture barriers in masonry walls (or concrete walls). Potential needs for moisture barriers in masonry walls are discussed below.

According to a Masonry Construction, Troubleshooting Q&A, Dampproofing the Cavity Face; “…In a well-built wall with an open cavity, dampproofing on the face of the block is not needed. The dampproofing, however, can provide additional protection.”

The need for a moisture barrier in a masonry cavity wall will ultimately depend on moisture management and the condensation potential.

One of the key items to consider in a moisture management strategy is the size of the drainage cavity. There is a code minimum for a 1-inch drainage space for masonry veneers (TMS 402 Sections 12.2.2.6 through 12.2.2.9). However, to minimize mortar bridging, a larger air space is often suggested. As the masonry veneer units are being placed, the bed and head joint mortar protrudes into the drainage cavity. According to Masonry Construction, Wall Cavities: Design vs. Construction, 1997; “…The air space should be 1-1⁄2 to 2 inches wide—large enough that masons can keep it mostly free of mortar. An airspace less than 1-1⁄2 inches wide is difficult to keep clear of mortar droppings, and an airspace less than 1 inch wide is almost impossible to keep clean.” The need for a moisture barrier will be dependent on the size of the drainage cavity. As the drainage cavity increases in size (greater than 1 inch), the need for a moisture barrier is lessened.

The need for a moisture barrier in a masonry cavity will also depend on the condensation potential (Refer to Are vapor retarders required or needed in masonry walls?). Dewpoint theory predicts condensation in a system at any point where the actual and dewpoint temperature lines cross. The need for a vapor retarder in a masonry wall should be determined by a dewpoint analysis. The software is available to building owners, designers and contractors1. If the dewpoint is shown to be in the dry zone (interior wythe), then a vapor retarder should be considered. If the dewpoint is shown in the wet zone and occurs in the thermal layer, then a moisture barrier should be considered.

The National Concrete Masonry Association, NCMA TEK 19-02B, Design for Dry Single wythe Concrete Masonry Walls, includes recommendations for moisture management for single wythe walls:

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. Dry concrete masonry walls are obtained when the design and construction addresses the movement of water into, through, and out of the wall.

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.

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. For details incorporating these NCMA recommendations, see MIM Generic Wall Design details.

1 Special thanks to Brent Jacobs, Commercial Channel Manager – Michigan

  DuPont Specialty Products Division, brent.jacobs@dupont.com

 Resources:

International Code Council (2018). International Building Code, 2018. International Code Council.

International Code Council (2015). International Building Code, 2015. International Code Council.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Building Code Requirements for Masonry Structures (TMS 402-11/ACI 530-11/ASCE 5-11)

Dampproofing the Cavity Face, Troubleshooting Q&A, (November 1996). Masonry Construction (495)

Wall Cavities: Design vs. Construction ( August 1997). Masonry Construction. file:///C:/Users/dan/Downloads/Concrete%20Construction%20Article%20PDF_%20Wall%20Cavities_%20Design%20vs.%20Construction.pdf

National Concrete Masonry Association, NCMA TEK 19-02B, Design for Dry Single wythe Concrete Masonry Walls

Design: Fire

Resource A of the IEBC provides detailed guidance for evaluating fire resistance of archaic materials, defines as those utilized prior to the 1950s, including concrete masonry units (CMUs). The CMU size, percent thickness, and aggregate type must be known to use the tables in the IEBC.

Section 722 of the IBC provides information on calculating the fire resistance of materials for new construction, including tables that list CMU wall fire resistance ratings based on the equivalent thickness and type of aggregate used in the CMUs. For similar guidance, ACI/TMS 216 can be consulted.

The equivalent thickness of the CMU wall is calculated as the net volume of masonry divided by the product of the unit length and height, where these parameters are determined in accordance with ASTM C140. An estimated equivalent thickness can be obtained by consulting NCMA TEK 7-1C Fire Resistance Ratings of Concrete Masonry Assemblies, which lists values for typical two-core units. However, significant changes were made to the ASTM standard for hollow CMU after the publication of NCMA TEK 7-1C, renderings its information invalid for newer units.

Both the IBC and ACI/TMS 216.1 categorize CMU aggregate into four (4) types, listed in order from lowest fire resistance to highest fire resistance:

  • Calcareous or siliceous gravel (other than limestone)
  • Limestone, cinders, or air-cooled (unexpanded) slag
  • Expanded clay, expanded shale, or expanded slate
  • Expanded slag or pumice

Table 3.1 of ACI/TMS 216 lists the fire resistance rating of the CMU wall based on the minimum equivalent thickness and type of aggregate used in the CMU. IBC Table 722.3.2 expands this table to provide fire resistance ratings in quarter hour increments.

As a first step, the tables should be consulted based on the estimated average equivalent thickness in found in NCMA TEK 7-1C, provided that the construction predates 2009. If the required fire resistance rating can be achieved regardless of the type of aggregate used, then no further effort is required, unless the required thickness value is close to the estimate. If the value is close, or if the required fire resistance rating cannot be achieved unless certain types of aggregate are present, then the equivalent thickness and/or aggregate type should be verified. Equivalent thickness can be determined by removing several units and assessing them in accordance with ASTM C140. Aggregate type can be determined by subjecting the CMU to petrographic (microscopical) analysis.

EXAMPLE: Consider an existing 10-inch CMU wall circa 1970. According to NCMA TEK 7-1C, the typical two-core 10-inch CMU has an equivalent thickness of 4.5-inches. If a 2-hour fire resistance rating is required, the wall is sufficient no matter what type of aggregate is in the CMU because the required equivalent thickness ranges from 3.2 to 4.2-inches. If a 3-hour rating is required, however, the wall is only sufficient if it has all expanded slag, pumice, expanded clay, expanded shale, and/or expanded slate as its aggregate. The first resistance rating is not sufficient if the CMU includes other types of aggregate.

Resources:

International Code Council (2018). International Building Code, 2018. International Code Council.

International Code Council (2015). International Building Code, 2015. International Code Council.

International Code Council (2018). International Existing Building Code, 2018. International Code Council.

International Code Council (2015). International Existing Building Code, 2015. International Code Council.

American Concrete Institute (2014). ACI/TMS 216.1-14 Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, 2014. American Concrete Institute.

ASTM Standard C140-03, “Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units,” ASTM International, West Conshohocken, PA, 2003, www.astm.org

National Concrete Masonry Association. (2018). TEK 07-01D Fire Resistance Ratings of Concrete Masonry Assemblies. https://ncma.org/resource/fire-resistance-ratings-of-concrete-masonry-assemblies/

If an existing masonry wall is determined to have a fire resistance rating less than that required (Refer to How does one determine the fire resistance rating of an existing, single wythe, hollow concrete masonry unit (CMU) wall? for more information), one option is to add wall finished on one or both exposed surfaces to improve its fire resistance.

The following finishes add to the wall’s fire resistance rating, whether applied to one surface only or to both surfaces, when installed in compliance with ACI/TMS 216.1 Section 5.3 or IBC Section 722.3.2.5:

  • Portland cement-sand plaster
  • Gypsum-sand plaster
  • Gypsum-vermiculite or perlite plaster
  • Gypsum wallboard

The fire resistance contribution(s) of the finish(es) is(are) calculated in accordance with IBC Sections 722.3.2.1 through 722.3.2.4 or ACI/TMS 216.1 Section 5.2. For each finish type and thickness, two sets of calculations of finished wall fire resistance must be made:

  1. The first calculation set assumes that the finish is on the non-fire-exposed side
  2. The second calculation set assumes that the finish is on the fire-exposed side

The smallest of these calculated values represents the fire resistance rating of the finished wall.

For a CMU wall with a finish that contributes to the fire resistance rating, the masonry alone is required to provide not less than one-half of the total required fire resistance. Also, the contribution of the finish on the non-fire-exposed side of the wall cannot exceed one-half of the masonry’s contribution alone.

Resources:

American Concrete Institute (2014). ACI/TMS 216.1-14 Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, 2014. American Concrete Institute.

If an existing masonry wall is determined to have a fire resistance rating less than that required (Refer to How does one determine the fire resistance rating of an existing, single wythe, hollow concrete masonry unit (CMU) wall? for more information), one option is to fill the hollow cells of the CMUs. Generally, this approach is only practical when the top of the wall is accessible so that the fill material can be poured in from the top and complete filling can be achieved.

Per ACI/TMS 216.1, the following cell fill materials are approved for improving fire resistance:

  • Sand, pea gravel, crushed stone, or slag that complies with ASTM C33
  • Pumice, scoria, expanded shale, expanded clay, expanded slate, expanded slag, expanded fly ash, or cinders that comply with ASTM C331
  • Perlite that complies with ASTM C549
  • Vermiculite that complies with ASTM C516

If the cells can be completely filled with one of these approved materials, then the equivalent thickness of the filled CMU wall is equal to the actual unit thickness which results in a substantial increase in fire resistance rating.

EXAMPLE: Consider an existing 10-inch CMU wall with an equivalent thickness of 4.5-inches. Suppose that a 4-hour fire resistance rating is required. The required minimum equivalent thickness, per ACI/TMS 216.1, ranges from 4.7-inches to 6.2-inches (depending on the aggregate type), so the existing wall is not adequate. If the cells are completely filled with one of the approved cell fill materials, then the equivalent thickness is the actual unit thickness, or 9.625-inches. In that case, the wall easily meets the required fire resistance rating.

Resources:

American Concrete Institute (2014). ACI/TMS 216.1-14 Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, 2014. American Concrete Institute.

The answer depends on what, if anything, is in the cells that are not grouted. If the ungrouted cells are completely filled with one of the code-approved materials, then the equivalent thickness of the wall is equal to the actual unit thickness (Refer to Can the fire resistance rating of an existing, single wythe, hollow concrete masonry unit (CMU) wall be improved by filling the cells? for more information).

If the ungrouted cells are void or are not completely filled with one of the code-approved materials, then the fire resistance rating is calculated in the same manner as for an ungrouted single wythe CMU wall. Thus, the effect of the grouted cells is neglected (Refer to How does one determine the fire resistance rating of an existing, single wythe, hollow concrete masonry unit (CMU) wall? for more information).

Resources:

International Code Council (2018). International Building Code, 2018. International Code Council.

International Code Council (2015). International Building Code, 2015. International Code Council.

American Concrete Institute (2014). ACI/TMS 216.1-14 Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, 2014. American Concrete Institute.

Design: Intersecting Walls

Rigid strap anchors are only required at the intersection of participating walls, which comprise part of the lateral force resisting system, when unit interlock or reinforced bond beams are not part of the construction at the intersection (Refer to How should intersecting masonry walls be connected? for more information).

Rigid strap anchors should not be installed where they are not necessary because the projecting portions of the metal strap could pose a safety hazard to persons on the project site if the projecting ends are not protected. Participating walls should be identified specifically as such by notes on the drawings. When required, strap anchors should be provided in accordance with MIM Generic Wall Design Committee Detail 2/S-2 shown below:

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Wall intersections may be required to meet one of three conditions:

  1. Transfer of all forces – All forces must be able to be transferred when the intersecting walls are participating walls and are both part of the lateral force resisting system (shear walls).
  2. Transfer of out-of-plane forces only – When a wall (first wall) is relying upon another wall (second wall) for lateral support, but the first wall is non-participating (not part of the lateral force resisting system), then the intersection must only transfer forces that are acting out-of-plane on the first wall.
  3. Transfer of no forces – Due to differential support or loading conditions, it may be desirable for no forces to be transferred at a wall intersection.

Transfer of all forces at an intersection, including shear, can be achieved by one of three methods:

  1. At least 50% of the masonry units at the interface must interlock (overlap),
  2. Steel anchors of minimum size 1/4-inch x 1.5-inch x 28-inch, including 2-inch long bends at each end, must be grouted into the intersection at a maximum spacing of 48-inches on center, or
  3. Intersecting reinforced bond beams must cross the intersection at a maximum spacing of 48-inches on center.

A steel anchor detail, which is used to transfer all forces at an intersection in the absence of unit overlap or reinforced intersecting bond beams, is shown in MIM Detail 2/S-2 below (Refer to When are rigid steel connectors (strap anchors) required for anchoring intersecting masonry walls? for more information).

When the wall relies on an intersecting wall for lateral support (transfer out-of-plane forces) only, with no shear (in-plane force) transfer, joint reinforcement or mesh hardware cloth are commonly used. Other metal ties/anchors that provide equivalent connection to joint reinforcement or mesh hardware cloth may be employed. However, TMS 402 currently explicitly permits this type of connection in intersecting walls designed by the Empirical provisions and in intersecting partition walls only.

The 2022 edition of TMS 402 is expected to describe how to anchor partition walls to structural walls so as to provide lateral support only.

  • Intersecting walls shall be anchored so as to transfer out-of-plane lateral load from the partition wall to the structural wall.
  • Masonry partition walls shall be isolated within their own plane at the intersection, except as required for gravity support of the walls.
  • Isolation joints and connectors at the intersections of masonry partition walls and structural walls shall be designed to accommodate the vertical and horizontal deformations of the structural wall.

A mesh hardware cloth detail, which is used to transfer out-of-plane forces only, is shown in MIM Detail 1/S-2 below:

When it is desirable to prevent transfer of all forces at a wall intersection, a movement joint (expansion or contraction) is formed at the intersection. Clay masonry expansion joints are detailed in BIA Technical Note 18A and concrete masonry control joint details are shown in NCMA TEK 10-2C.

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Joint Reinforcement: Less is More. (July 2015). Masonry Magazine, 44-50.

https://www.masonrymagazine.com/blog/2015/06/24/joint-reinforcement-less-is-more/

Selecting Joint Reinforcement. (June 2014). The Construction Specifier Magazine, 50-58.

https://www.constructionspecifier.com/selecting-joint-reinforcement/

National Concrete Masonry Association. (2019). TEK 10-02D Control Joints for Concrete Masonry Walls-Empirical Method. https://ncma.org/resource/control-joints-for-concrete-masonry-empirical-method/

Brick Industry Association. (May 2019). Technical Notes on Brick Construction 18A accommodating Expansion of Brickwork. https://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/tn18a.pdf?sfvrsn=0

Design: Movement Control

Movement joints are constructed within masonry to accommodate predicted volume changes of the masonry materials as well as relative movement between masonry and adjacent materials. Movement joints are finished with sealant to prevent water entry while the joint changes dimension. Masonry movement joints may be described as one of three types:

  1. Expansion joints,
  2. Contraction or control joints, or
  3. Isolation joints

Expansion joints (EJs) are used to accommodate volume expansion of clay masonry. According to the Brick Industry Association (BIA), clay masonry undergoes irreversible moisture volume expansion over time, with the majority of the size change occurring during the first year after manufacture. As the clay masonry increases in size, or volume, the movement (expansion) joint decreases in width. The sealant in the EJ needs to be capable of continuing to function as intended by remaining intact and adhered to the joint sides while being squeezed.

Control joints (CJs) are used to accommodate volume shrinkage of concrete masonry, including cast stone. According to the National Concrete Masonry Association (NCMA), concrete masonry undergoes irreversible volume shrinkage over time. Most of the size change occurs during the first year after manufacture. As the concrete masonry decreases in size, or volume, the CJ increases in width. The sealant in the CJ needs to be capable of continuing to function as intended by remaining adhered to the joint sides, without interior tearing, while being stretched.

Isolation joints (IJs) are designed and constructed to permit differential movement between masonry and adjacent materials, such as windows, doors, and non-masonry façade cladding materials. The differential movement may be parallel or perpendicular to the length of the movement joint. Therefore, the sealant in the joint may be squeezed smaller or stretched wider or stretched diagonally or may be subjected to a combination of these movements. The sealant in the IJ needs to be able to continue to function without tearing or losing adhesion to the joint sides while accommodating these various distortions.

Masonry movement joints are separate and distinct from building expansion joints. Masonry movement joints are designed and constructed within the masonry wythe only but building expansion joints extend through the entire building structure and finishes.

Resources:

National Concrete Masonry Association. (2019). TEK 10-02D Control Joints for Concrete Masonry Walls-Empirical Method. https://ncma.org/resource/control-joints-for-concrete-masonry-empirical-method/

Brick Industry Association. (May 2019). Technical Notes on Brick Construction 18 Volume Changes – Analysis and Effects of Movement. https://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/tn18.pdf?sfvrsn=0

National Concrete Masonry Association. (2001). TEK 10-04 Crack Control for Concrete Brick and other Concrete Masonry Veneers. https://ncma.org/resource/crack-control-for-concrete-brick-and-other-concrete-masonry-veneers/

The architect/engineer is responsible for determining the locations of masonry movement joints and identifying those locations for the contractor to construct (Refer to What are masonry movement joints? for more information).

TMS 402/602 addresses responsibility for determining the locations of movement joints. TMS 402 Section 1.2.1 directs the architect/engineer to, “Show all Code-required drawing items on the project drawings, including…provision for dimensional changes resulting from elastic deformation, creep, shrinkage, temperature, and moisture.” In the Mandatory Requirements Checklist, TMS 602 provides additional guidance to the architect/engineer by listing under Part 3 – Execution, Article 3.3 D.6 Movement joints, a note to the architect/engineer that states, “Indicate type and location of movement joints on the project drawings.”

Movement joints in a masonry veneer are typically shown on the architectural drawings. Architects typically locate the joints in accordance with the recommendations of the Brick Industry Association (for a clay masonry veneer) and the National Concrete Masonry Association (for a concrete masonry veneer). Architects also typically consider aesthetics when choosing the locations of movement joints.

Single wythe concrete masonry walls and the concrete masonry inner wythe of a multi-wythe wall are typically structural members used to resist gravity loads and lateral loads. IN structural walls, movement joints are typically shown on the structural drawings. These movement joint locations must be carefully selected by the engineer to avoid impairing structural integrity of the wall and to be consistent with the structural behavior intended by the engineer during design (Refer to How does an engineer determine the location of masonry movement joints in a structural masonry wall? for more information).

Movement joint locations identified by the architect/engineer should be shown graphically on plan or elevation drawings. A narrative note like, “Locate movement joints at a spacing not to exceed 25-feet on center” on the drawings allows the contractor to decide the actual locations of movement joints, which may not be consistent with the architect/engineer’s design intent. When some movement joints are shown on the architectural drawings and others are shown on the structural drawings, coordination between the architect and engineer is required.

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Following are some of the issues that the engineer should address when selecting movement joint locations and designing movement joint details to be shown on the structural drawings (Refer to Who is responsible for determining the locations of masonry movement joints? for more information):

  1. Should a movement joint extend through a bond beam? The answer depends on the purpose of the bond beam. Bond beams at floor and roof levels act as tension ties (also known as the tension chord) for the floor or roof diaphragm, and/or as a bearing surface for gravity loads, and, therefore, usually should not be interrupted by a movement joint. Whether movement joints should extend through intermediate bond beams (other than at floor and roof levels) depends on how the engineer intended that bond beam to function and how the movement joint is detailed at the bond beam.
  2. Is the wall acting as a shear wall to resist in-plane forces from wind or seismic loads? If it is a shear wall, what is the wall length upon which the engineer is relying for strength to resist those in-plane forces. Movement joints should not be designed between ends of designated shear wall segments.
  3. What is the intended behavior at a wall intersection? If the two walls are intended to work together as a shear wall (as a flanged shear wall, which is stronger than a straight shear wall segment) to resist wind and seismic loads, then a movement joint should not be designed at the intersection of the walls. Alternatively, if the two walls need to act independently so as not to transfer loads from one wall to another, then a movement joint at the intersection may be appropriate.
  4. Where are the point loads from floor or roof beams bearing on the wall and how far away from those bearing points do the movement joints need to be placed? A movement joint should not be designed within the length of wall that directly supports that point load (Refer to TMS 402 on how concentrated loads disperse through a bond beam and disperse through masonry below the bond beam). Also consider that vertical loads cannot be transferred across a movement joint or a continuous mortared head joint as would occur with stack bond construction.
  5. Is the wall spanning vertically between lateral supports at the top and bottom, or horizontally between columns, pilasters, or cross walls at each end of the wall? If a wall is spanning horizontally, a vertical movement joint should not be designed within that wall length unless the joint is carefully designed to transfer out-of-plane forces.
  6. Are shaft walls being relied upon to brace the structure against lateral loads by acting as shear walls? If so, were the shaft walls intended to act separately as straight wall segments or were they intended to resist the loads by working together as a box shape? Only the engineer knows how the shaft walls were designed, so the engineer must decide whether movement joints should be omitted from those walls.
  7. Do the walls have adequate horizontal reinforcement to resist shrinkage stresses without movement joints? If the horizontal reinforcement is designed properly (Refer to NCMA TEK 10-3), then the movement joints in those walls may not be required by the engineer.

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

National Concrete Masonry Association. (2003). TEK 10-03 Control Joints for Concrete Masonry Walls-Alternative Engineered Method. https://ncma.org/resource/control-joints-for-concrete-masonry-walls-alternative-engineered-method/

This FAQ specifically assumes that the cracking has occurred due to shrinkage in the concrete masonry and not due to settlement or structural reasons.

According to NCMA TEK 10-01A, “Cracking resulting from shrinkage can occur in concrete masonry walls because of drying shrinkage, temperature fluctuations, and carbonation. These cracks occur when masonry panels are restrained from moving.” To control shrinkage cracking in concrete masonry walls, control joints are placed along with horizontal joint reinforcement. This approach does not eliminate cracking; however, it limits the crack width.

By today’s standards, NCMA TEK 10-2D, control joints should be spaced at a minimum of 1.5 times the height of the wall or 25-feet when standard 9-gauge (W1.7) horizontal joint reinforcement is placed every 16-inches on center for 8-inch high units. For 4-inch (half high) units, control joints should be spaced at a minimum of 1.5 times the height of the wall or 20-feet when standard 9-gauge (W1.7) horizontal joint reinforcement is placed every 12-inches on center. From corners, control joints should be spaced within a distance equal to half of the control joint spacing. Control joints can be placed near unreinforced openings, or away from reinforced openings.1 When mapping existing cracks on wall elevations, the following distances should be noted to assist in the evaluation:

  1. Distance between cracks
  2. Distance from corners
  3. Distance from openings

NCMA TEK 8-01A provides the following repair information regarding shrinkage cracking:

  1. In considering implementing control joints in the existing wall, determination will have to be made in their location and spacing.1
  2. If the cracking is not extensive, confined primarily to the mortar joints, and relatively stable (not moving); then consider conventional tuckpointing.
  3. For smaller cracks, there are a variety of clear water repellents that can resist water penetration when the crack is less than 0.02-inches in width.
  4. For larger cracks that are continuing to move, consider filling the crack with a flexible sealant.

Footnotes

  1. For locating and spacing recommendations, reference NCMA TEK 10-2D and the MIM Control Joint Guide available on their website, masonryinfo.org. For cutting in control joints, reference NCMA TEK 8-01A.

Resources

National Concrete Masonry Association. (2004). TEK 08-01A Maintenance of Concrete Masonry Walls. https://ncma.org/resource/maintenance-of-concrete-masonry-walls/

National Concrete Masonry Association. (2019). TEK 10-02D Control Joints for Concrete Masonry Walls-Empirical Method. https://ncma.org/resource/control-joints-for-concrete-masonry-empirical-method/

National Concrete Masonry Association. (2003). TEK 10-03 Control Joints for Concrete Masonry Walls-Alternative Engineered Method. https://ncma.org/resource/control-joints-for-concrete-masonry-walls-alternative-engineered-method/

Design: Stack Bond

Stack bond is one bond pattern that falls into the category of “not laid in running bond”, where running bond is defined as placing units in successive courses so that head joints are offset at least one-quarter of the unit length. TMS 402 does require horizontal reinforcement when the masonry is not laid in running bond. TMS 402 requirements apply to concrete masonry, clay masonry, and dimension stone masonry, but not autoclaved aerated concrete masonry.  Cast stone masonry is also currently excluded from the TMS 402, but the same amount of horizontal reinforcement should be used when cast stone is not laid in running bond.

Masonry that is not laid in running bond is required to contain horizontal reinforcement in the amount of 0.00028 multiplied by the gross vertical cross-sectional area of the wall, using specified dimensions. The horizontal reinforcement may be placed in mortar joints or in bond beams and may be spaced up to 48-inches on center as required in Section 4.5 of the TMS 402.

Masonry veneer that is not laid in running bond is required to have horizontal joint reinforcement consisting of at least one wire of size W1.7 spaced at a maximum of 18 inches on center as required by Section 12.2.2.10 of TMS 402.

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

National Concrete Masonry Association. (2003). TEK 10-03 Control Joints for Concrete Masonry Walls-Alternative Engineered Method. https://ncma.org/resource/control-joints-for-concrete-masonry-walls-alternative-engineered-method/

Stack bond is one bond pattern that falls into the category of “not laid in running bond”, where running bond is defined as placing units in successive courses so that head joints are offset at least one-quarter of the unit length. In addition to the requirement for horizontal reinforcement (Refer to Are there Code requirements for joint reinforcement in masonry laid in stack bond? for more information), several other Code requirements are imposed when the masonry is not laid in running bond. These primarily affect the structural design, but also affect the amount of reinforcement, particularly in higher Seismic Design Categories.

  1. As stated in Section 5.1.2.2 of TMS 402, “For masonry not laid in running bond and having bond beams spaced more than 48-inches center-to-center, the width of the compression area used to calculate member capacity shall not exceed the length of the masonry unit.”
  2. As stated in Section 5.1.3.2 of TMS 402, “For assemblies not laid in running bond, concentrated loads shall not be distributed across head joints.”
  3. Under the Allowable Stress (Chapter 8) provisions, the allowable flexural tensile stress for masonry not laid in running bond is zero unless the masonry includes continuous grout sections parallel to bed joints (Refer to Table 8.2.4.2 of TMS 402 for additional information).
  4. Under the Allowable Stress (Chapter 8) provisions, the allowable shear stress is reduced when masonry is not laid in running bond and fully grouted. The allowable shear stress is zero when masonry is not laid in running bond and is not fully grouted.
  5. Under the Strength Design (Chapter 9) provisions, the modulus of rupture for masonry not laid in running bond is zero unless the masonry includes continuous grout sections parallel to the bed joints (Refer to Table 9.1.9.2 of TMS 402 for additional information).
  6. Under the Strength Design (Chapter 9) provisions, the nominal shear strength is reduced when masonry is not laid in running bond and fully grouted. The nominal shear strength is zero when masonry is not laid in running bond and not fully grouted.
  7. As stated in Section 7.3.2.6 of TMS 402 for Special Reinforced Masonry Shear Walls, the maximum spacing of vertical and horizontal reinforcement is reduced from 48-inches to 24-inches for masonry not laid in running bond, while the additional maximum spacing limits of 1/3 the shear wall height and 1/3 the shear wall length still apply. The minimum cross-sectional area of horizontal reinforcement is also increased from 0.0007 to 0.0015 when masonry is not laid in running bond. Masonry not laid in running bond shall also be gully grouted and constructed of hollow open-end units or two wythes of solid units.
  8. As stated in Section 7.4.5 of TMS 402 for masonry elements in Seismic Design Categories E and F, “Masonry not laid in running bond in nonparticipating elements shall have a cross-sectional area of horizontal reinforcement of at least 0.0015 multiplied by the gross cross-sectional area of masonry, using specified dimensions. The maximum spacing of horizontal reinforcement shall be 24-inches. These elements shall be fully grouted and shall be constructed of hollow open-end units or two wythes of solid units.”
  9. TMS 402 includes additional requirements for autoclaved aerated concrete masonry that is not laid in running bond in Chapter 11.

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Design: Veneer

Yes, concrete masonry veneer should include horizontal joint reinforcement placed in mortar bed joints including embedded lap splices of at least 6 inches. Because it is a concrete masonry veneer, the veneer will undergo net irreversible shrinkage due to:

  1. Wetting and drying cycles
  2. Carbonation
  3. A decrease in temperature (reversible)

Because the net effect is shrinkage, a combination of horizontal joint reinforcement and proper placement of control joints1 should be employed to reduce the potential for shrinkage cracking. Note that joint reinforcement should be galvanized or stainless steel and placed with at least 5/8-inch of mortar cover at the weather exposed face and 1/2-inch of mortar cover at the non-weather exposed face. Typically, the industry suggests the horizontal joint reinforcement be placed every 16-inches vertically for 9-gauge wire (W1.7). The horizontal joint reinforcement may be separate and placed in alternate joints or connected to adjustable veneer anchors (seismic clip)2.

Footnotes

  1. MIM has developed a control joint guide and spreadsheet for determination of control joint spacing available on their website, masonryinfo.org
  2. The MIM Generic Wall Design Committee has developed veneer details which incorporate these recommendations and are available on their website, masonryinfo.org

Resources

National Concrete Masonry Association. (2001). TEK 10-04 Crack Control for Concrete Brick and other Concrete Masonry Veneers. https://ncma.org/resource/crack-control-for-concrete-brick-and-other-concrete-masonry-veneers/

National Concrete Masonry Association. (2005). TEK 12-02B Joint Reinforcement for Concrete Masonry. https://ncma.org/resource/joint-reinforcement-for-concrete-masonry/

Selecting Joint Reinforcement. (June 2014). The Construction Specifier Magazine, 50-58.

https://www.constructionspecifier.com/selecting-joint-reinforcement/

The TMS 402 permits masonry veneer to be designed by either the alternative engineered method (Refer to TMS 402 Section 12.2.1 for more information) or the prescriptive requirements for anchored masonry veneer (Refer to TMS 402 Section 12.2.2 for more information).

According to the prescriptive requirements, veneer that is backed by wood framing is not required to have shelf angles because the height of such veneer above the support is limited to 30-feet, except that gables are permitted to be 38-feet tall (Refer to TMS 402 Section 12.2.2.6.1 for more information). When the veneer is backed by cold-formed steel framing, the veneer must be supported at each story above 30-feet to the plate or 38-feet to the gable (Refer to TMS 402 Section 12.2.2.7.1 for more information). The veneer height limits for wood-framed and steel-framed backing are permitted to be waived if an engineering analysis is performed in accordance with the alternative engineered method outlined in Section 12.2.1. However, shelf angles are not required for structural support of prescriptively designed masonry veneer backed by concrete masonry unit (CMU) construction, regardless of the veneer height, provided that the veneer is supported on an appropriate foundation.

When the veneer wythe is clay masonry and the backup wythe is CMU, the differential volume change movements (due to clay masonry expansion and CMU shrinkage, as well as thermal movements, creep, etc.) must be considered in the design, regardless of whether the alternative engineered method or prescriptive requirements are used. The taller the wall, the more significant the differential movement. Detailing at penetrations through the wall must be carefully designed and executed. As a practical matter, the height of buildings with such walls should not exceed four stories because it becomes more difficult for detailing (at the top, at ties between wythes and openings) to accommodate the magnitude of differential movement that result from taller structures. Anticipated volume changes can be calculated in accordance with TMS 402 Section 4.2.

When the veneer wythe is the same CMU material as the backup wythe, but the cavity between the wythes is insulated, some differential movement will also occur between wythes, although less than with a veneer wythe of clay masonry. The anticipated differential movement should be calculated so that appropriate details can be developed to accommodate it.

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Detailing to Accommodate Vertical Expansion. (June 1994). Masonry Construction Magazine, 254-256. https://www.concreteconstruction.net/how-to/construction/detailing-to-accommodate-vertical-expansion_o

Designing for Differential Movement. (April 2005). The Construction Specifier Magazine, 44-56. https://masonryinfo.org/wp-content/uploads/2016/05/designing-for-differential-movement-clay-brick-veneer-over-wood-frame.original.pdf

Brick Industry Association. (May 2019). Technical Notes on Brick Construction 18A Accommodating Expansion of Brickwork. https://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/tn18a.pdf?sfvrsn=0

Recessing of masonry courses adds architectural interest to a building façade. However, there are three aspects of recessing that should be considered:

  1. Recessing creates a “ledge” on the outside face, at the bottom of the recess. Just as with raked and struck mortar joints, this “ledge” increases the risk of water infiltration at the mortar/unit interface. The International Masonry Institute (IMI) recommends installing a mortar wash at this “ledge” at the same time the units are placed on the mortar bed. However, if the recessed course is at or below eye level, this mortar wash will be visible which will impact aesthetics.
  2. The impact on the cavity behind the veneer, where the recessed course creates a projection into the drainage space. This projection must not decrease the air space behind the veneer to less than the 1-inch minimum required by the TMS 402. Also, consideration should be given to the impact of that projection on the ability of water that has penetrated the veneer and entered the cavity to flow freely downward to the flashing and weep holes. Like the mortar wash on the outside face, IMI recommends a mortar wash on the inside face of the veneer at the top of the recessed course. Unless a cavity is wide enough, however, this mortar wash could be difficult to accomplish and may contribute to mortar droppings in the cavity.
  3. The reduction of flexural strength, or resistance to cracking. When the veneer consists of solid units (net cross-sectional area of 75% or more per ASTM), which are laid with full mortar bed, the reduction in strength at a slightly recessed course is small and insignificant. However, when hollow units (net cross-sectional area less than 75% per ASTM) are constructed with recessed courses, strength reduction can be significant because these units are typically laid with face shell mortar only and there is little to no face shell overlap at the recessed course. Consequently, hollow units should not be used when recessed courses are desired, unless they are solidly filled with mortar or grout. When the magnitude of the recess equals or exceeds the depth to the core holes in solid units, extra care is required during construction to mitigate the potential for water entry into those core holes.

The magnitude of recessing in veneer is governed by the corbel provisions of TMS 402 Section 5.5. The maximum offset per course must not exceed one-half the nominal unit height nor one-third the nominal unit thickness. If successive courses are each recessed, the total offset should not exceed one-half the veneer wythe thickness. Whether one course or multiple courses are recessed, the back, or inside, surface of the veneer must remain within one-inch of plane.

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

ASTM Standard C216-16, “Standard Specification for Facing Brick (Solid Masonry Units Made from Clay of Shale),” ASTM International, West Conshohocken, PA, 2016, www.astm.org

ASTM Standard C652-17a, “Standard Specification for Hollow Brick (Hollow Masonry Units Made from Clay of Shale),” ASTM International, West Conshohocken, PA, 2017, www.astm.org

ASTM Standard C1634-06, “Standard Specification for Concrete Facing Brick,” ASTM International, West Conshohocken, PA, 2006, www.astm.org

ASTM Standard C55-17, “Standard Specification for Concrete Building Brick,” ASTM International, West Conshohocken, PA, 2017, www.astm.org

ASTM Standard C73-17, “Standard Specification for Calcium Silicate Brick (Sand-Lime Brick),” ASTM International, West Conshohocken, PA, 2017, www.astm.org

ASTM Standard C129-17, “Standard Specification for Nonloadbearing Concrete Masonry Units,” ASTM International, West Conshohocken, PA, 2017, www.astm.org

Details to Avoid. (July 1990). Masonry Construction Magazine, 292-294.

Wall Cavities: Design vs. Construction. (August 2997). Masonry Construction Magazine, 445-446.

Often, clay masonry is incorporated into exterior concrete masonry veneer, or concrete masonry veneer is used in clay brick masonry veneer as accent bands. The bands add architectural interest to the wall and can help hide horizontal elements such as flashing and expansion joints. However, combining these two materials within one wythe of masonry requires special detailing due to the different material properties.

When a band of concrete masonry is located within a clay brick veneer, one method of detailing is to place horizontal joint reinforcement in the mortar joints immediately above and below the band. Also, anchors should be installed within the band whenever the band consists of more than one course. For bands higher than two courses, joint reinforcement should also be placed within the band itself at a spacing of 16-inches on center vertically. Ideally, the joint reinforcement and ties should be placed in alternate joints so that one does not interfere with placement of the other. Some designers, however, prefer placing joint reinforcement in every bed joint in the concrete masonry band. In this case, a tie that accommodates both tie and wire in the same mortar joint should be used, such as a seismic clip wall tie shown below from NCMA TEK 05-02A:

Alternatively, a slip plane can be incorporated into the interfaces between the concrete masonry courses and clay masonry courses to allow unrestrained longitudinal movement between the two materials. This can be accomplished by placing building paper, polyethylene, flashing, or a similar material in the horizontal bed joints above and below the band. When hollow masonry units are used for the band, the slip plane below the band should incorporate flashing so that water draining down the cores of the band can be directed out of the wall at the flashing. When slip planes are used, joint reinforcement should be incorporated into the concrete masonry band in the veneer. The exposed mortar joint at the top and bottom of the band should be raked back and sealed with an appropriate sealant to prevent water penetration at these joints. If the bottom joint incorporates flashing, however, sealant should not be installed to cover the edge of the flashing or the weeps. One detail of a band with slip planes is shown below from NCMA TEK 05-02A:

When slip planes are used, the veneer should be anchored to the backing within 12-inches above and below the isolated band. Also, anchors should be installed within the band whenever the band consists of more than one course. In addition to incorporating joint reinforcement in the concrete masonry, expansion joint spacing should be decreased to reduce the potential for masonry cracking. Experience has shown that vertical expansion joints in the clay masonry veneer should extend through the concrete masonry band, as well, and be placed at a maximum of 20-feet along the length of the wall. Local experience may require reducing the expansion joint spacing from 20-feet to 16-feet. Although concrete masonry construction typically requires control joints rather than expansion joints, control joints should not be used in the concrete masonry band at the expansion joint location.

The recommendations to control differential movement for clay brick masonry bands in a concrete masonry wythe are remarkably similar to those for a concrete masonry band in a clay brick veneer: joint reinforcement above and below the band, wall ties within the band, and wall ties within 12-inches above and below the band. Seismic clip-type wall ties are recommended, as they provide an adjustable wall tie and joint reinforcement in one assembly. With this construction, it is imperative that the concrete masonry veneer control joints not contain mortar where they extend through the clay brick band that would restrict brick expansion.

Cast stone is another material that may be used in feature bands within clay masonry, or vice versa. When the cast stone units are hand held units that are bedded in mortar, banding of cast stone in clay masonry and banding of clay masonry within cast stone masonry should be treated the same as if the cast stone was concrete  masonry. When large cast stone units are installed with gravity supported anchors rather than mortar bedding, the cast stone masonry should be isolated from the clay masonry.

Resources:

National Concrete Masonry Association. (2002). TEK 05-02A Clay and Concrete Masonry Banding Details. https://ncma.org/resource/clay-and-concrete-masonry-banding-details/

Brick Industry Association. (May 2019). Technical Notes on Brick Construction 18A Accommodating Expansion of Brickwork. https://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/tn18a.pdf?sfvrsn=0

Cast Stone Institute. (June 2018). Allowing for Movement of Masonry Materials. https://www.caststone.org/bulletins/technical_bulletin_52_allowing-for-movement-of-masonry-

The air space is located directly behind the masonry veneer. This space allows for proper drainage along with flashing and weeps. The principle of a drainage type wall is water that may penetrate from the exterior to the interior through the masonry veneer can flow downward within the air space once the water reaches the inboard surface of the veneer. The amount of water penetrating the masonry veneer will be based on the unit material properties, detailing, and workmanship. For example, one could expect more penetrating water with greater exposure from raked out mortar joints, a sloping roof with no gutters, and head joints that are not full and not compressed. A flashing is installed at the bottom of the air space to collect the water and direct it via the weeps and along the flashing plane to the exterior. According to BIA Technical Note 7; “Properly designed, detailed and constructed drainage wall systems provide excellent water penetration resistance.” According to BIA Technical Note 23A, “Drainage walls are recommended for maximum resistance to rain penetration and minimum efflorescence.” From Masonry Online Construction, “I have heard people recommend using weep vents at the bottom and top of walls to help dry them out following a rain…The faster the walls dry out following rains, the less time available for salts and soluble compounds within the mortar to be carried to the surface…Although vents help dry walls following a rain, those near the top can also allow water to easily enter the walls during rains. Water penetrating the top vents can increase the potential for efflorescence and other moisture related problems. In this case, vents may do more harm than good. There are, however, creative ways of installing vents at the top of walls that protect them from rains…”

The total cavity width would typically include the combined widths of the air space, insulation, and sheathing (depending on the backup).

Footnotes

  1. The TMS 402/602-22 is still being developed and, as such, these numbers have not been finally adopted and codified.

Resources

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Brick Industry Association. (November 2017). Technical Notes on Brick Construction 7 Water Penetration Resistance – Design and Detailing. https://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/7-water-penetration-resistance-design.pdf?sfvrsn=0

Brick Industry Association. (June 2019). Technical Notes on Brick Construction 23A Efflorescence – Causes and Prevention. https://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/tn23a.pdf?sfvrsn=0

Most of the brick in walls designed and constructed today are classified as a veneer. A veneer is a masonry wythe that provides the exterior finish of a wall system that transfers our-of-plane load directly to a backing. A veneer is an element that is not considered to add strength or stiffness to the wall assembly. This FAQ will address the brick anchor embedment for anchored veneer. Anchored veneer is secured to and supported laterally by the backing through anchors and supported vertically by the foundation or other structural elements. Thus, an anchored veneer supported by the foundation will not contribute to the effective seismic weight.

Article 3.4E of the TMS 602 addresses veneer anchors (corrugated sheet-metal anchors, sheet metal anchors, and wire anchors) for solid units and hollow units. A solid masonry unit is defined as having a net cross-sectional area of 75 percent or more of its gross cross-sectional area. A hollow masonry unit is defined as having a net cross-sectional area of less than 75 percent of its gross cross-sectional area.

For solid units, anchors are required to be embedded in mortar a minimum of 1-1/2-inch with at least 5/8-inch mortar cover to the outside face.

For hollow units, anchors are required to be embedded in mortar or grout a minimum of 1-1/2-inch with at least 5/8-inch mortar or grout cover to the outside face. Proper anchorage of veneer anchors into hollow units can be achieved by:

  1. Mortaring anchors in bed joints or on the cross-webs of the units
  2. Grouting the cells or cores adjacent to the anchor
  3. Following the anchor manufacturer’s requirements for installing the anchor into the cell or core above or below the bed joint and filling the cell or core containing the anchor with mortar or grout

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.

Chapter 12 of the TMS 402 Building Code Requirements for Masonry Structures contains provisions relating to the design of veneers. The Code Commentary to Section 12.2.2.10.3, Seismic Design Categories E and F, states; “The 1995 through 2011 editions of the MSJC Code required that masonry veneer in Seismic Design Categories E and F be provided with joint reinforcement, mechanically attached to anchors with clips or hooks. Shaking table research (Klinger et al, 2010(b)) has shown that the requirement is not necessary or useful so the requirement was removed in the 2013 edition of the MSJC Code.”

Resources:

Society, The Masonry (2016). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2016. The Masonry Society.

Society, The Masonry (2013). TMS 402/602 Building Code Requirements and Specification for Masonry Structures, 2013. The Masonry Society.