Masonry is a highly skilled trade where the final appearance of a project can be negatively impacted by poor workmanship. There is an entire standard dedicated to masonry construction that can be referenced to address most of the issues that designers are concerned about when using masonry.
The purpose of this page is to summarize the workmanship standard defined by CSA and how to properly reference them with project specifications. Some projects may require greater attention to detail and tighter tolerances on the constructed masonry due to project specific factors and can be specified in addition to the standard outlined in CSA.
This page is part of a larger series of specification examples meant to highlight cases where vague or poorly written items within a specification document have lead to issues on masonry jobs across Canada.
Disclaimer
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 specification typically appears:
X.Y Installation Tolerances:
X.Y.a Install masonry work to a plane flatness and exposed end tolerance of 3 mm in 3000 mm.
Discussion points to consider when specifying tolerances:
This specification example seen above is poorly written for several reasons. “Plane flatness” is an ambiguous term that does not accurately describe the application of this tolerance. The 3 mm measurement is similarly ambiguous in the fact that it does not state whether this is a 3 mm absolute tolerance or a plus/minus tolerance of 3 mm. The former would suggest a plus/minus 1.5 mm allowance which is half of the latter interpretation, and quite a significant change for this tolerance measurement. This tolerance, at best, is half the allowable tolerance required in CSA A371-14 and interpreted as an absolute value of 3 mm, it is one quarter the allowable tolerance within CSA A371-14.
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. It can also be expected that tighter tolerances will come with a premium on the installation cost. 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.
Suggested changes to the specification:
X.Y Installation Tolerances:
X.Y.a Installation tolerances of masonry shall conform to those in the CSA A371 and as specified in this Section. If there is a discrepancy between the tolerances specified in this Section and those specified in CSA A371, the more stringent tolerance will govern.
X.Y.b Surfaces of walls, columns, edges, and corners must have a relative alignment of ± 3 mm in 3,000 mm.
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