Movement joints are a critical component of masonry design. They are to be specified by the designer with their locations clearly shown on the contract documents in order to allow for expansion, contraction, and other movement between sections of masonry to avoid cracking.
The purpose of this page is to offer insight and recommendations on how these can be specified when required in a masonry project.
This page is part of a larger series of specification examples meant to highlight cases where vague or poorly written items have lead to issues on masonry jobs across Canada.
The information contained here is intended to serve as educational content for designers, specifiers, or contractors. It is not to be relied upon for formal technical advice, as masonry projects may have details and considerations that are unique to a particular project and may be beyond the scope of the content of this page.
If there are any questions or concerns regarding masonry design or construction, CMDC offers technical assistance to our supporting members, as well as the design community.
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How the structural note typically appears:
X. Provide block wall control joint at location shown on architectural drawings. Maximum spacing to be at 12.0 meters. Reinforce one cell on either side of joint with 2 – 15m vertical and fill with concrete. All horizontal reinforcing to run continuous through control joint.
Discussion points to consider when specifying movement joints:
In this structural note horizontal reinforcement is being specified to be continuous through a vertical movement joint in the wall. The details given in the structural note raise several important considerations.
- The term control joint is not a term used in Canadian design. The term Movement Joint is the modern name used in the CSA suite of standards as well as the National Building Code of Canada.
- The purpose of a movement joint within a wall may serve one or more of structural, environmental, and serviceability requirements. The purpose of a movement joint is to permit unrestrained movement between adjacent masonry wall sections, or between masonry walls and non-masonry elements. Reinforcement may be provided across such a joint in 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 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.
- Movement joint locations are to be specified by the designer on the contract documents. A maximum spacing of 12.0 m does not provide enough details to the installer as to the exact locations where movement joints should be placed. A distance of 12.0 m between movement joints is a large distance by most industry standards. Typical industry recommendations are to provide movement joints at spacings ranging from 6.0 m (20′) to 7.6 m (25′), however this can vary due to the masonry unit, the amount of reinforcing in the wall, and the expected service conditions.
- 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).
- Concrete should never be used as a substitute for grout. Concretes will not meet the aggregate gradation requirements for a CSA A179-14 proportion specified grout and is typically mixed to a lower slump and water content than that of masonry grouts. The use of plasticizers or water reducing agents in concrete will cause issues with grout flow and bond in the wall.
Suggested changes to the specification:
X. Movement joints shall be provided as indicated in the drawings. Vertical reinforcement in the form of 1-15M bar shall be placed in one cell on either side of a movement joint. Cells containing reinforcement shall be grouted with a grout meeting the proportion specifications of CSA A179-14.
Y. Horizontal reinforcement shall be terminated as specified in the drawings at vertical movement joint locations.
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