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.

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.