When it comes to masonry construction, mortar joints are how a mason can provide quality workmanship even when the units themselves and support conditions are not perfect. While there are other workmanship items addressed on pages available here, the size of mortar joints can be specified in a manner consistent with CSA standards.
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.
How the specification typically appears:
X.Y.a All joints must be 10 mm thick. Masonry courses to be uniform height and both vertical and horizontal joints to be of equal and uniform thickness.
Discussion points to consider when specifying mortar joint thickness
Mortar joints help the mason accommodate the permissible variation between masonry units (dimension, distortion or warpage, and out-of-square). They also help accommodate permissible variations in the overall length of the masonry (i.e.: non-modular lengths between windows) and tolerances of the supporting and adjacent structures. As a result, acceptable masonry construction practice in Canada allows for some variability to the mortar joint thickness within the construction tolerances of CSA A371-14. It is impossible to construct any masonry without tolerances. For common types and uses of masonry construction the standard allows for a variation in mortar joint thickness of ± 3 mm. As a result, the bed and head joint thickness for constructed masonry may vary between 7 and 13 mm (other than the first course of masonry).
Tighter tolerances than those within CSA A371-14 can certainly be specified within a project specification, however, they must be both practical and well described. In addition, the masonry units selected for the project must also have a higher degree of precision and a smaller permissible variation in dimensions. Tolerances that appear within the specifications should be carefully considered by both the designer and the installer when they deviate from industry accepted values contained in the CSA A371-14. If the designer wishes to have tolerances of construction that are more restrictive than the CSA A371-14 it should be clearly stated in a manner consistent with the wording of the standard and come with the expectation that tolerances above those considered to be industry standard come with increased cost considerations and in certain situations actually decrease the aesthetic qualities of the masonry wall by chasing unrealistic tolerances.
Suggested changes to the specification:
X.Y.a The constructed thickness of the first mortar bed joint at the base of unit masonry built on a non-masonry element shall be from 6 to 20 mm, except that for masonry veneer built on shelf angles or lintels, the constructed thickness shall be from 0 to 13 mm.
X.Y.b Mortar bed and head joints, other than the first mortar bed joint, shall have a thickness of 10 mm ± 3 mm.
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