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.

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.

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.