When placing the veneer on the shelf angle, it is recommended that no more than one-third of the width of the veneer extends past the edge of a shelf angle. According to Clause 6.4.2 of CSA A371-14:

6.4.2 Projection of a nonloadbearing wall or veneer

The projection of a nonloadbearing wall or veneer beyond the edge of a supporting member such as a shelf angle or edge of a beam shall not exceed 30 mm or one-third of the width of the wall or veneer, whichever is more. The projection of the units beyond the bearing support shall not contain voids.

Similarly, masonry designed using Part 9 of the National Building Code of Canada are governed by a similar provision in clause 9.20.12:

9.20.12.3. Corbelling for Masonry Veneer

     (1) Masonry veneer resting on a bearing support shall not project more than 25 mm beyond the supporting base where the veneer is at least 90 mm thick, and 12 mm beyond the supporting base where the veneer is less than 90 mm thick.

     (2) In the case of rough stone veneer, the projection, measured as the average projection of the stone units, shall not exceed one-third the bed width beyond the supporting base.

The loads acting on the shelf angle must be determined, and the design of steel sections used for shelf angles must adhere to relevant steel design standards, particularly the CSA S16. Similarly, the design of anchors must conform to the specific material design standards of the  structural backup  material. Requirements for the support of masonry that are relevant to design of shelf angles, including rigidity requirements, can be found in Clause 4.8 of CSA S304-14.

It is important to keep in mind that shelf angles are prone to corrosion as they are left exposed within the cavity’s airspace. While proper installation and overlapping of flashing materials can offer protection against direct moisture, the underside and backside of the steel itself may still be exposed to external air, potentially leading to long-term corrosion risks. Corrosion protection requirements for shelf angles are indicated in Clause 4.11.3.5.1 of CSA S304-14. For conditions wherein CSA A370-14 requires veneer ties to have Level 3 corrosion protection (stainless steel), the shelf angle must be hot-dip galvanized. Otherwise, if ties only require Level 2 corrosion protection (hot-dip galvanized), then the shelf angle may be protected only with a primer coating conforming to CSA S16 as long as it is also protected by a durable flashing  or in case the service life of the building is less than 25 years.

The shelf angle serves as a vital structural connection between the exterior veneer and the backup wall. However, this connection also creates a direct pathway for thermal transfer, bypassing the insulation layer. Shelf angles act as thermal bridges in masonry veneer walls, resulting in relatively small but noticeable adverse effects on the overall thermal resistance of the wall system. The larger the area of steel that passes through the insulation layer, the greater the negative impact on the whole-wall R-value.

The trend towards increased cavity sizes in masonry walls has brought about a twofold advantage for thermal performance. Firstly, the wider cavity allows for more insulation to be installed. Secondly, the use of stand-off shelf angles reduces the extent of steel that crosses the insulation layer, when compared to shelf angles connected directly to a floor slab or wall. A fundamental principle in masonry building envelope design is the necessity for continuous insulation over the exterior of the backup wall. Therefore, it is crucial to ensure that insulation is always placed behind the shelf angle, when stand-off supports are utilized, in order to maintain the continuity of insulation and preserve thermal performance.

Design requirements for masonry veneers can be found in CSA S304-14 Design of Masonry Structures, Clause 9. Within the requirements, the Standard provides limits on both the unit material and unit dimensions (Clause 9.1.2) for Unit Masonry Veneer.

9.1.2  Unit material and dimension limitations

Unit masonry veneer shall be construction using clay (shale) masonry units, calcium silicate (sand-lime) masonry units, or concrete masonry units; the individual units shall be limited in height to not more than 200 mm, limited in length to not more than 400 mm, and limited in thickness to not less than 75 mm.
Note: Masonry units exceeding the specified maximum size limits may be considered to satisfy the requirements for unit masonry veneer, provided that independent testing confirms suitability for unit masonry construction methods, tolerances, and load transfer to structural backing.

The size limitations of masonry units have been harmonized throughout all of the material, construction, and design CSA Masonry Standards. Units within those size limitations are suitable for unit masonry construction methods and tolerances due to the extensive research and field experience that has been conducted on units within this size range as well as decades of satisfactory performance of structures featuring these materials. Units exceeding these size limitations are not covered by the standards and therefore the minimum requirements, performance, and tolerances may not be applicable.

Manufacturers are responsible for providing adequate testing to ensure that units which exceed the dimensional limits to unit masonry may still be designed and installed using masonry CSA standards. Test data, analysis, and relevant specifications shall be provided to the designer and masonry contractor to confirm unit suitability for unit masonry construction methods, tolerances, and load transfer to structural backing. This article provides some of the possible issues that should be considered for testing but does not represent a comprehensive list.

Each masonry standard serves a specific purpose. More information about the landscape of masonry-related codes and standards is available here.

CSA A370-14 is a material standard. It provides material requirements for the manufacturing of masonry ties, anchors and fasteners (collectively termed connectors).

CSA A370-14 provides material properties such as minimum connector strength, maximum connector free play, and maximum spacing limits.

CSA A371-14 is a construction standard. It provides requirements for the construction of masonry.

CSA A371-14 outlines guidance for many different aspects of construction, including but not limited to the following: tolerances of construction, reinforcement cover and tying requirements, mortar and grout placement, and maximum spacing of ties.

The design of masonry ties are solely covered by the CSA S304-14. Masonry ties must be designed to transmit lateral loads applied to the veneer from wind or earthquakes, the design of the masonry ties is subject to material properties such as the strength of the tie, expected differential movement, and construction properties such as the material used for the back-up.

For a masonry building that qualifies for design using Annex F, the masonry veneer may be designed using empirical methods. To design masonry ties using Annex F there are several important things to consider:

1. The building must adhere to all of the requirements of Clause F.1.1. This includes restrictions on the height of the masonry and the seismic hazard index.
2. Veneers must be supported by a structural backing of concrete or masonry and must have a slenderness ratio, kh/t, less than or equal to 20. Design of veneers on wood or steel stud back-up walls are not permitted through Annex F and are required to be designed to satisfy the requirements of Clause 9 of CSA S304-14.
3. Only prescriptive connectors may be used with Annex F empirical design. CSA A370-14 by default requires connectors to be designed for factored loads according to the CSA S304-14. While CSA A370-14 does also provide manufacturing and design requirements for prescriptive ties, the use of these provisions are limited to the same criteria that also apply to empirical design (low seismicity, limited wind loads, reduced building height, etc.). Prescriptive connectors must also be spaced at no more than the maximum spacing limits provided in Clause 10 of the CSA A370-14 as well as follow all of the requirements listed in CSA A370 for the specific connector used.

For cases where Annex F does not apply, ties for the masonry veneer must be designed according to Clause 9 of the CSA S304-14 with their spacing based on the factored load and the factored resistance of the tie. Maximum spacing requirements are provided by CSA A370-14 and CSA S304-14. These do not represent a conservative solution without accompanying engineering analysis. The intent of this maximum spacing requirement is to limit cracking of the masonry veneer and has no relevance to strength or performance of the tie itself.

It is important that the most recent editions of relevant CSA standards are referenced. In the case of uncertainty, one can find the relevant edition of the standard in the list of referenced documents accompanying the building code in effect for any specific area. For the current edition of the national model code, National Building Code of Canada 2015, the relevant editions of the CSA standards are circa 2014.

The four facets are explained below. These four facets completely define the characteristics of the block, according to the standard, and no further clarification is required.

The first facet indicates the solid content of the units. Hollow units, whose solid content is generally between 50 and 55%, are designated by the letter “H”; semi-solid units, with a solid content exceeding 75%, are designated by the letters “SS”; and solid units, the net cross-section of which is equal to 100% of the gross section (without voids), are designated by the letters “SF”.

The second facet indicates the specified compressive strength of the units: 10 for 10 MPa, 15 for 15MPa, 20 for 20MPa, etc.

For a concrete masonry unit to meet the requirements at a given specified strength, there is a statistical formula that must be satisfied within the block standard, CSA A165.1-14, that is based on 95% confidence of exceeding that specified strength. For example, a specified 15 MPa block would test around 18 MPa on average, and required to be stronger than that depending on the scatter of the testing results. Manufacturers are also required by CSA A165 to have compression testing for each mix design done within the last year, serving as an additional measure for quality assurance that is built into the standard.

Designers should note that higher strength units are not inherently “better” than the lowest strength that otherwise meet the structural design requirements. By simply specifying CMU following the 4-facet system and referencing CSA A165.1-14, the provisions discussed here are automatically included and there is no need to add further conservatism by further increasing the specified compressive strength.

The third facet indicates the density and maximum water absorption of the units: “A” for a normal density (greater than 2000 kg/m³) with a maximum absorption of 175 kg/m³; “B” for a density of 1800 to 2000 kg/m³ and a maximum absorption of 200 kg/m³; etc.

Units are typically specified as either Type A (“normal”) density, or Type C (“lightweight”) density. Depending on the concrete mix used to achieve the lightweight, Type C density classification, there may be increase in the fire resistance rating that can be considered using the equivalent thickness pathway within the National Building Code of Canada.

The fourth facet indicates whether the units are moisture-controlled (type “M”) or whether there is no limit to the moisture content (type “O”). Moisture-controlled units have different humidity limits depending on the total linear drying shrinkage. It is generally recommended not to specify moisture controlled units and to accommodate shrinkage through the regular placement of movement joints.

A concrete block can be specified as follows: H/15/A/O which would translate to a hollow unit, with a specified compressive strength of at least 15 MPa, normal density, and not requiring additional moisture control measures.

These four facets completely define the characteristics of the block, according to the standard, and no further clarification is required. The standard allows producers flexibility to meet these and other requirements of the standard through different modes of production. For example, the standard does not distinguish between a block that is cured at room temperature or high temperature, or at normal atmospheric pressure or autoclaved, or if the blocks are produced with new technology. In all cases, the minimum strength, shrinkage and absorption limits, and dimensional and cracking tolerances (and other aesthetic aspects) are the same, according to the standard, for all blocks designated with the same four facets. Therefore, all blocks that comply with CSA A165.1 and are designated with the same four facets are considered aesthetically and structurally equivalent, under the standard, including for differential movements.

It is not uncommon to hear these terms used interchangeably throughout the masonry industry. The term “control joint”, which would indicate that the detailing of this joint is to release internal tensile stresses in the masonry wall caused by shrinkage, has been phased out of the CSA Masonry Standards in lieu of a more generic term “movement joint” as defined below:

Movement joint — a vertical or horizontal separation built into a masonry wall to reduce restraint and the corresponding stresses by accommodating movement of the wall or movement of other structural elements adjacent to the walls.

The term movement joint covers both, expansion and contraction of masonry, and accommodates for differential movement between the masonry and other parts of the structure.

Movement Joint is the modern term used in the CSA suite of standards as well as the National Building Code of Canada.

Movement joint locations are to be specified by the designer in the contract documents. A maximum spacing of 12.0 m, as shown in the example of problematic specification, does not provide enough details to the installer as to the exact locations where movement joints should be placed. In addition, a distance of 12.0 m between movement joints is a large distance by most industry standards. Typical industry recommendations are to provide vertical movement joints at spacings ranging from 6.0 m (20′) to 7.6 m (25′), however, this can vary due to the masonry units, the amount of reinforcing in the wall, and the expected service conditions.

The purpose of a movement joint within a wall may serve one or more of structural, environmental, and serviceability requirements. Movement joint permit unrestrained movement between adjacent masonry wall sections, or between masonry walls and non-masonry elements. Horizontal reinforcement may be provided across such a joint in a manner that still facilitates this movement (e.g., the detailing of slip dowels whereby reinforcing bars are embedded in a sleeve and lubricated to permit lateral movements while providing dowel action). Movement joints may be crossed by horizontal reinforcement at certain locations where it is structurally necessary but will have minimal impact on serviceability, such as at the top of the wall to resist diaphragm cord tension forces. However, this is localized to specific locations typically at the top of bottoms of walls and not over the wall height.

Horizontal joint reinforcement should not cross a movement joint, unless specific detailing has been specified and approved at a set location by the structural engineer (e.g., to transfer out-of-plane loading with one end debonded within the wall). Horizontal joint reinforcement that is continuous through a movement joint, restricts horizontal movement of the masonry wall, allowing a significant concentration of stresses along the length of the wall and resulting in the formation of cracks.

In the example of problematic specification, vertical reinforcement is specified as 2-15M bars in a single cell. In some unit sizes the use of two reinforcing bars in a single cell will lead to reinforcement congestion and grouting issues. A single vertical bar is recommended in 20 cm units and will provide adequate structural integrity. Two bars may be acceptable in 25 cm or 30 cm units as long as the spacing and position requirements of CSA A371-14 and CSA S304-14 are met. Depending on the required steel, designers could replace the 2-15M bars (As = 400 mm²) with a single 20M bar (As = 300 mm²) or a single 25M bar (As = 500 mm²).

The example of problematic specification also mentions the use of “concrete” to fill the cells with vertical reinforcement. Concrete should never be used as a substitute for grout. Concrete will not meet the aggregate gradation requirements for a CSA A179-14 proportion specified masonry grout and is typically mixed to a lower slump and water content than that of masonry grouts. The use of concrete with plasticizers or water reducing agents could cause issues with flow and bond in the wall. Grout meeting the requirements of CSA A179-14 should be specified in masonry construction.

This is by far the most common path for specifying mortars and grouts. In this case, the mortar type (Type S or N) is specified to meet the requirements for proportion specified mortars in Table 3 or Table 4 of CSA A179-14. CSA A179-14 provides installers with a prescriptive mix design to follow for either mortar type depending on the materials used (Portland cement, masonry cement or mortar cement). The standard has requirements for the gradation curves of sand and outlines how mortars are to be mixed. Field testing of proportion specified mortars may include tests for the sand/cementitious material ratio or compressive strength of mortar cubes. For a proportion specified mortar there is no minimum value of compressive strength which must be met. Rather, field testing is done against a benchmark value, typically established at the start of construction, to ensure consistency in mortar mixes throughout a project.

For mortars prepared at the job site when conventional materials and conventional procedures are expected, Proportion Specification may be specified (CSA A179-14, proportions of the ingredients comply with Table 3 or Table 4, as applicable) and no minimum value of compressive strength needs to be specified.

A lesser used compliance pathway is property specification for mortars and grouts. This compliance path is open for new materials or mixes that may otherwise fall outside the proportion specification. An example of this might be ready-mixed mortars that are batched and mixed off site and use additives to extend their useful life. These types of mortars require testing to ensure that they meet a baseline of performance equal to at least that provided by proportion specified mortars. This requires multiple tests, one of which is based on the type of mortar and whether it is a jobsite prepared or laboratory prepared mortar. Table 6 of CSA A179 provides minimum compressive strength values of mortar cubes at 7 and 28 days. So, for a Type S mortar prepared at the jobsite, the required minimum compressive strength values would be 5 MPa and 8.5 MPa for the 7 d and 28 d test respectively.

For mortars manufactured off-site in a batching plant (like ready-mixed mortars), Property Specification should be specified, and a minimum compressive strength value may be specified but not lesser than strength requirements in Table 6 of CSA A179-14. It should be noted that certain pre-packaged, pre-bagged or silo products of dry materials simply contain the components of a proportion specified mortar, in compliance with Table 3 or Table 4 of CSA A179 and should be treated as such. However, other dry-mixed property specified mortar products contain admixtures and/or other components and must meet the requirements of CSA A179 through property specification.

When the designer requires on-site introduction of an admixture or other materials to improve the performance of the mortar, then Property Specification should be followed. In such cases,  the designer should work with the masonry contractor to develop a mortar mix that meets the required properties.  A ratio of aggregate to cementitious material in the mortar may be established (monitoring batching, mixing, and handling procedures) or a minimum compressive strength value may be specified but not lesser than strength requirements in Table 6 of CSA A179-14. Monitoring of properties (i.e., compressive strength of mortar cubes) is often used in lieu of monitoring batching, mixing, and handling.

In this case, as with most projects involving new construction, the specification needs to reference the mortar and grout standard, CSA A179.

Finally, it is important that the most recent editions of relevant CSA standards are referenced. In the case of uncertainty, one can find out the relevant edition of the standard in the list of referenced documents accompanying the building code in effect for your specific area. For the current edition of the national model code, National Building Code of Canada 2015, the relevant editions of the CSA standards are circa 2014.

Clause 8.1 from CSA A371-14 states that wire used for bed joint reinforcing shall have a minimum diameter of 3.0 mm and a maximum diameter of half the joint thickness or 5 mm, whichever is less. In practice, there are two common diameter sizes for joint reinforcing, 3.65 mm (termed “regular”) or 4.76 mm (termed “heavy duty”). In most cases, regular 3.65 mm joint reinforcement is preferred and should be specified because it is easier to cut, install, and lay units on, compared to heavy duty bed joint wire reinforcement. Heavy duty wire is more difficult to work with on site due to its increased rigidity and increased thickness relative to the mortar joint size.

The size of bed joint wire reinforcement required depends on the design. In general, when bed joint wire reinforcement is needed for crack control (e.g., over very long lengths of wall between movement joints, around openings, or as required in stack or decorative pattern masonry) then regular (3.65 mm) size wire should be used. The need for heavy duty wire is typically a result of meeting prescriptive reinforcing ratios for seismic design requirements or resisting in-plane shear forces in loadbearing walls. Therefore, its use must be determined by the designer and detailed within the contract documents.

When specifying bed joint wire reinforcement for cored clay brick or unreinforced concrete block, truss-type bed joint wire may be used. Truss-type bed joint wire reinforcement is fabricated by securing the cross-rods between wires at an angle to form a truss. The cross-rods will interfere with any vertical reinforcing bar placement in the masonry because of how the cross-rod passes through the open cell (across the middle).

Specifying truss reinforcing in masonry walls that will also be vertically reinforced will create great difficulty in placing the vertical reinforcing. Typical masonry construction practice will have the vertical reinforcing bars placed after the wall is constructed. If there are diagonal cross wires present within the cells it will make the placement of this reinforcing extremely difficult and will likely push the placement of outside of its tolerance window. In some cases, contractors may cut the diagonal cross wires of truss joint reinforcement to facilitate the placement of vertical rebar. However, CMDC generally discourages that practice.

To avoid situations where the bed joint reinforcing will interfere with the vertical reinforcement, truss type bed joint reinforcing should not be specified with vertically reinforced walls.

There is no recognized structural difference between ladder- and truss-type bed joint wire reinforcement. Ladder-type bed joint wire reinforcement has the advantage of locating cross-rods perpendicular to the main reinforcing wires in the face shells. Therefore, cross-rods can be arranged so that they lie on, or close to, unit webs ensuring they do not interfere with vertical bar placement. To alleviate any possible conflicts on site, ladder-type bed joint wire reinforcement should always be used with concrete block masonry.

Since vertical reinforcing bars are not easily or typically placed in clay brick or 10 cm concrete block masonry units, truss-type bed joint wire reinforcement may be used. When hollow or semi-solid 15 cm, 20 cm, 25 cm, or 30 cm concrete block masonry units are used then only ladder-type bed joint wire reinforcement should be used. This is the safest approach because of the possibility for these units to contain vertical reinforcing bars, however, truss type joint reinforcement can be acceptable with these types of units when designed and constructed as unreinforced.

Other than for veneer applications, the vast majority of bed joint wire reinforcement used in masonry construction does not require any additional corrosion protection requirements (i.e., plain steel is acceptable and preferred).

Typical bed joint wire reinforcement assemblies (ladders and trusses) are manufactured to be 40 mm narrower than the actual unit width resulting in a mortar cover of 20 mm. CSA A371-14 provides cover requirements for all reinforcing in masonry elements. Except where required for veneer walls, single wythe exterior walls, foundation walls, or interior columns and beams, all reinforcing bars (20M and smaller, without corrosion protection) or bed joint wire reinforcement in masonry walls require only 20 mm of cover from the masonry surfaces.

Designers are reminded that concrete masonry walls (e.g., shear walls and partition walls) are considered to be “interior” when they are located on the inside face of the wall cavity behind the building envelope’s waterproof membrane. These walls are not considered to be exposed to any direct precipitation, or weather, as defined by CSA A371-14. Exceptions can be made, for instances, where masonry is used within certain industrial settings such as  a sewage treatment plant, or for other special cases such as for a decorative fountain or pool, etc. when corrosion resistance for interior walls becomes a concern. However, in most applications plain steel embedded with at least 20 mm of mortar cover is sufficient for corrosion protection of bed joint wire reinforcement.

In cases where bed joint wire reinforcement is required in masonry that is exposed to weather (single-wythe walls, veneer walls), or potentially corrosive environments (industrial settings), then CSA S304-14 Clause 4.11.3 requires that the joint reinforcement must have the same corrosion protection as required for ties in accordance with CSA A370-14. Where corrosion protection is required, it should be indicated in the project plans in accordance with the levels of corrosion protection described in CSA A370:

• Level 1: no corrosion protection (plain steel or mill galvanized)
• Level 2: hot-dip galvanized after fabrication (requirements, including coating thickness are indicated in CSA A370)
• Level 3: stainless steel (acceptable grades of stainless steel indicated in CSA A370)

Spacing requirements for bed joint wire reinforcement are determined by the designer. There is no one-size-fits all spacing requirement for bed joint wire reinforcement. Since it is most commonly required to meet a prescriptive area of reinforcement (e.g., crack control) or to resist in-plane shear forces (e.g., seismic), the size and spacing requirements for bed joint reinforcement are dependent on many possible factors.

Crack control in masonry can be achieved with bed joint wire reinforcement, most commonly in concrete brick and concrete block walls. In such cases, designers may refer to industry recommended guidelines for its use (click here to open in new browser tab) and the recommended methods to determine if and how much may be required. Typically, crack control in very long spans of masonry, or around openings, is achieved by providing a horizontal reinforcement ratio based on net wall area of approximately 0.002. Seismic design requirements for non-loadbearing and loadbearing masonry may also require prescriptive horizontal reinforcement ratios based on the gross wall area per CSA S304-14. However, prescriptive maximum spacing limits and minimum reinforcement ratios may also account for the presence of bond beams. Furthermore, loadbearing walls may be governed by the need for bed joint wire reinforcement to resist in-plane shear forces, which itself may present different prescriptive limits.

Spacing of bed joint wire reinforcement should not be left to the specifications; instead, it should be established during the design of the masonry elements and based on the requirements of CSA S304-14 and CSA A371-14. There are few cases, in addition to stack pattern masonry, where a common size or spacing across all walls is necessary or justified; however, in many cases bed joint wire reinforcement that is added to meet no other definable design objective rationally calculated represents an unnecessary added cost.

Masonry mortar must meet the requirements of CSA A179-14: Mortar and grout for unit masonry. Under this standard there are two separate compliance paths to specify mortar: proportion specifications and property specifications.

Proportion specified mortar is for jobsite mixing where CSA approved materials are to be mixed to the volume-based proportions given in Table 3 or Table 4 of the Standard. Property specified mortars allow for manufacturers to use innovative materials to enhance the properties and/or behaviour of masonry mortar but must follow strict testing requirements to ensure acceptable performance.

The effect of these different types of mortar on the strength of a masonry assemblage is reflected in Table 4 of CSA S304-14: Design of masonry buildings. A higher assemblage strength, f’_m, is assigned to masonry assemblages with Type S mortar compared to those with Type N mortar. The strength of masonry assemblages also increases with increasing specified strength of the units, however the specified properties of Type S and Type N mortar does not change depending on the units used. In general, specifying a mortar strength greater than the minimum required by CSA A179 will not provide any benefit to the specified strength of masonry for design.

Proportion specification in CSA A179-14 sets the proportion, by volume, of Portland cement, lime, and sand, in accordance with Table 3 or Table 4 of the Standard, to be combined to achieve the desired Type S or Type N mortar. Although testing of site-prepared mortar, including compression testing, may be used as quality control to verify the mortar is being mixed to the correct proportions, there is no minimum compression strength required for proportion specified mortar – even for loadbearing applications. Proportion specified Type S and Type N mortars have a long history of good performance, when mixed using the correct materials to the correct proportions, for loadbearing masonry applications.

Property specifications in CSA A179-14 allow the designer to require any 28-day mortar cube strength they may need, so long as it is not less than those listed in Table 6. For Type S mortar, a minimum required 28-day mortar cube strength of 8.5 MPa and 12.5 MPa for jobsite prepared and laboratory prepared mortars, respectively. The lower strength requirements for jobsite prepared mortar accounts for the effects of increased water content to achieve higher flows, effects of retempering and age of mortar on the board, among other job site conditions. Research indicates that specifying a higher strength mortar than those detailed in Table 6 of CSA A179-14 may only yield a marginal increase in the overall compressive strength of the masonry assembly, fʹ_m. This marginal increase is even less apparent in assemblages with higher strength units and when units are grouted. Increased mortar strength offers no benefit to masonry strengths for design unless accompanying masonry prism testing is being undertaken in order to exceed the prescriptive values for fʹ_m given in CSA S304 Table 4. Additionally, higher strength mortars are achieved by increasing the cement content of the mix which will decrease the workability of the mortar. A mortar with low workability is more difficult for the masons to place properly and may increase the risk of bond problems between the mortar and the masonry units.

For mortars manufactured off-site in a batching plant (like ready-mixed mortars), Property Specification should be specified, and a minimum compressive strength value may be specified but not lesser than the strength requirements in Table 6 of CSA A179-14. It should be noted that certain pre-packaged, pre-bagged or silo products of dry materials may simply contain the components of a proportion specified mortar, in compliance with Table 3 or Table 4 of CSA A179 and should be treated as such. However, other dry-mixed property specified mortar products contain admixtures and/or other components and must meet the requirements of CSA A179 through property specification.

When the designer requires on-site introduction of an admixture or other materials to improve the performance of the mortar, then Property Specification should be followed. In such cases, the designer should work with the masonry contractor to develop a mortar mix that meets the required properties.  A ratio of aggregate to cementitious material in the mortar may be established (monitoring batching, mixing, and handling procedures) or a minimum compressive strength value may be specified but not lesser than strength requirements in Table 6 of CSA A179-14.  Monitoring of properties (i.e., compressive strength of mortar cubes) is often used in lieu of monitoring batching, mixing, and handling.

Use of mortars with the strengths given by the property specifications detailed in CSA A179-14 Table 6 has been shown to result in masonry compressive strengths meeting or exceeding those detailed in Table 4 of CSA S304-14. The best way to increase the compressive strength, fʹ_m, of a masonry assemblage is to specify concrete masonry units with a higher compressive strength. If a masonry strength is required that exceeds those provided in CSA S304-14 Table 4, testing of masonry prisms in accordance with clause 5.1.2 of CSA S304-14 must be conducted.

Designers occasionally mistakenly use historic approaches to estimate masonry strength by using empirical equations that relate block, grout, and mortar strengths to estimate the assemblage strength. Such equations predate limit states design of the CSA S304-14. Without prism testing there is no design benefit to specifying mortar properties that exceed those indicated in CSA A179-14. Furthermore, designers are reminded that mortar cubes, grout cylinders and concrete block units, as tested, do not represent in-situ wall properties and cannot serve as a rational basis to estimate assemblage strength. The loss of free moisture, confining effects of the units, and dimensional properties of mortar and grout in cube/cylinder form are completely different than those within a masonry assemblage. This is why the standard only recognises prism testing as a means to establish a masonry strength in excess of the values listed in Table 4 of CSA S304-14. Matching strengths of mortars or grouts to that of blocks has no theoretical or rational basis within the CSA S304-14 design standard.

Design requirements for masonry veneers can be found in CSA S304-14 Design of Masonry Structures, Clause 9. Within the requirements, the Standard provides limits on both the unit material and unit dimensions (Clause 9.1.2) for Unit Masonry Veneer.

9.1.2  Unit material and dimension limitations

Unit masonry veneer shall be construction using clay (shale) masonry units, calcium silicate (sand-lime) masonry units, or concrete masonry units; the individual units shall be limited in height to not more than 200 mm, limited in length to not more than 400 mm, and limited in thickness to not less than 75 mm.
Note: Masonry units exceeding the specified maximum size limits may be considered to satisfy the requirements for unit masonry veneer, provided that independent testing confirms suitability for unit masonry construction methods, tolerances, and load transfer to structural backing.

The size limitations of masonry units have been harmonized throughout all of the material, construction, and design CSA Masonry Standards. Units within those size limitations are suitable for unit masonry construction methods and tolerances due to the extensive research and field experience that has been conducted on units within this size range as well as decades of satisfactory performance of structures featuring these materials. Units exceeding these size limitations are not covered by the standards and therefore the minimum requirements, performance, and tolerances may not be applicable.

Manufacturers are responsible for providing adequate testing to ensure that units which exceed the dimensional limits to unit masonry may still be designed and installed using masonry CSA standards. Test data, analysis, and relevant specifications shall be provided to the designer and masonry contractor to confirm unit suitability for unit masonry construction methods, tolerances, and load transfer to structural backing. This article provides some of the possible issues that should be considered for testing but does not represent a comprehensive list.

Frequently, specifications indicating the use of masonry units larger than the definition of unit masonry also call for the application of tolerances contained in CSA A371-14, that may not be possible to meet with the larger masonry units. In particular, designers often comment on the alignment between adjacent units, noticeable under coincident lighting (e.g. from a surface-mounted light fixture), casting unwanted long shadows and giving the appearance of poor workmanship.

Masonry CSA standards’ requirements and tolerances may be applicable to units exceeding the dimension limitations if the manufacturer of the masonry units has completed independent testing for this unit to confirm items including:

1. The unit tolerances and physical properties meet the requirements of CSA A165-14; and
2. The masonry construction methods and tolerances contained within CSA A371-14 can be achieved; and
3. The loads can be transferred to the structural backing, including connector spacing and installation methods and differential movement details.

In all cases of masonry construction, it is recommended that designers should specify the construction of a “mock up” wall or “sample panel”, as a segment of a masonry assemblage or a stand-alone panel (CSA A371-14, Annex A) before the start of general masonry construction. This should be done in addition to any testing provided by the manufacturer.

Designers should be aware that while coincident lighting from a surface-mounted light fixture or sconce may be used to enhance the architectural features of rough or textured units, accenting the shadows created by the 3-dimensional geometry of the surface of the rough masonry wall (e.g. rough stone walls), this same effect may unexpectedly occur with coincident lighting on a smooth masonry wall surface. In such cases, minor construction imperfections (even those that may be within agreed construction tolerances), especially when long masonry units are used, may cast unwanted long shadows and give the erroneous visual appearance of unacceptably poor workmanship. If the resulting shadows on the masonry veneer cause any aesthetic concerns, it is suggested that a change to the lighting will achieve the desired aesthetic while maintaining cost effectiveness and durability for the intended building function.

The final consideration for veneer units would be the location and connections of the veneer to the back-up wall and the design of masonry ties. The spacing of ties selected based on their engineering design must consider the new unit dimensions and corresponding modular spacing available for placement of ties. Units that are taller or longer than unit masonry may require special considerations when designing tie systems that have non-standard spacing, increased stiffness or strength, and may require some type of mechanical fastening to the unit. Dimension cut stone, as an example, is a type of masonry unit that may exceed the dimensional limits for unit masonry that have special provisions provided by CSA S304 Appendix A. These provisions provide designers with a good background to how larger units may be accommodated.