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Information about CMDC, or even just masonry in general

Here are some of the more common questions that we get all the time

Questions are categorized on the left and listed below. Continue scrolling for more information and click or tab any question to expand our response.

Frequently Asked Questions

Can CMDC help me with questions about masonry on my house?

In general, CMDC works through members of the design community (engineering and architectural) as well as our masonry contractor members. In most cases, the most effective approach to address issues with your personal home is to get in touch with a design professional directly. They can assess the situation and, if necessary, utilize our services.

I need to hire an engineer. Can I contact CMDC to perform engineering services?

No. While we are staffed with qualified and licensed professional engineers, CMDC does not offer engineering consulting services in the form of stamped designs or drawings.

What does CMDC charge for consulting?

CMDC offers free technical assistance to members of the design community and our contractor members. While CMDC does provide consulting services in a few specialized and niche cases (click to learn more), we strongly advise seeking professional services from consulting firms that offer these services to the general public, which CMDC does not do.

Can CMDC come to do an inspection of masonry for me?

In general, CMDC collaborates with members of the design community, including engineering and architectural firms, and our masonry contractor members when they require technical assistance. In certain situations, these technical inquiries may necessitate an on-site visit; however, such visits are evaluated on a case-by-case basis. It’s important to note that CMDC does not offer fee-for-service consulting for masonry inspections. We are a resource to designers, not one of their competitors.

Does CMDC have a list of engineers, architects, or contractors they can recommend?

For CMDC to maintain objectivity and avoid any perceived bias, we cannot provide recommendations regarding specific designers or contractors. We recommend that when seeking a designer, you inquire about the up-to-date masonry education of their staff and whether they actively participate in any educational resources offered by CMDC. Masonry contractors who are members of a provincial association listed on our website (click for details) have access to CMDC services, and we highly recommend engaging a masonry contractor who is a CMDC member for your services.

Does CMDC sell codes and standards?

The National Building Code of Canada is available for free online. CMDC can provide electronic copies of masonry CSA standards A82, A165, A179 A370, A371 to designers that attend an educational seminar put on by CMDC. More information about how to request such a seminar can be found here. A hard copy version of CSA S304 is available within the textbook Masonry Structures: Behaviour and Design, 2nd Canadian Edition, which can be purchased here.

Does CMDC write codes and standards?

Our staff actively participate in the development of various codes and standards, both through voting and observation. However, it’s important to note that no single party is solely responsible for writing any standard or code. Codes and standards are created through a consensus-based process involving a diverse technical committee representing a broad spectrum of interests. While CMDC strives to support research programs that drive these changes, we are not the sole entity responsible for their development.

About CSA Standards and the Building Code

Are ASTM and CSA standards for masonry the same?

Designers should exercise utmost caution when citing an ASTM standard that is not directly referenced by either the National Building Code or one of our CSA standards. For example, the testing for the compressive strength of a concrete masonry unit (ASTM C140) is one such ASTM standard referenced in our Canadian standard CSA A165.1. However, it’s crucial to note that the testing of a masonry prism (ASTM C1314) differs significantly from the requirements outlined in the Canadian design standard for prism testing (CSA S304). While some ASTM and CSA standards may seem interchangeable, it is of paramount importance that only those standards referenced by the National Building Code of Canada are used in Canadian design.

Have the standards really changed that much since the last edition?

Users of the National Building Code of Canada will recognize the significant changes that have taken place with each recent new edition, which require strict compliance by building officials and authorities having jurisdiction. In a similar manner, the masonry standards referenced by the building code have also experienced substantial changes in each recent version. It is of paramount importance to ensure that you are using the relevant versions of the standards referenced in the current prevailing building code.

Where can I get the latest version of the code and masonry standards?

The National Building Code of Canada is available for free online. CMDC can provide electronic copies of masonry CSA standards A82, A165, A179 A370, A371 to designers that attend an educational seminar put on by CMDC. More information about how to request such a seminar can be found here. A hard copy version of CSA S304 is available within the textbook Masonry Structures: Behaviour and Design, 2nd Canadian Edition, which can be purchased here.

Are there any codes or standards for existing masonry structures?

At this time there are no specific Canadian codes or standards published by NRC or CSA that address the design of existing masonry structures. There are a number of resources that are available to designers and more information can be provided by reaching out to CMDC technical services directly.

General Questions about Masonry

Covering some broad, more general questions about masonry and how it fits in among other materials and systems in terms of cost, benefits, durability, and environmental impact.

Why build with masonry?

Similar to other building materials, there are times when using masonry just makes sense. Masonry carries a special aesthetic value deeply connected to Canadian history and a cultural heritage linked to some of the world’s most iconic historical structures. For many, masonry represents something ingrained in our culture. Masonry materials are typically produced locally, and they’re intimately tied to skilled craftsmanship and a level of hands-on artistry that’s often missing in mass-produced building materials. Many people appreciate masonry for its resilience and durability. Masonry often leads to buildings that are built to last, going above and beyond the minimum code requirements for durability, lifespan, fire protection, sound insulation, resilience, and strength. That’s why it’s the preferred choice for many of our most significant buildings and monuments. It’s closely associated with our proudest achievements, such as our places of worship, schools and universities, legislative buildings, hospitals, and emergency services – places that symbolize safety, importance, culture, history, and legacy.

Is masonry more expensive than other materials?

It’s hard to answer this question in a simple way, but it’s something we should think about when making decisions that go beyond our own lifetimes. There’s a lot of real-world data out there that shows masonry can be more cost-effective than other materials for both structural purposes and as a veneer. While we usually focus on current costs in these discussions, it’s essential to mention masonry’s proven long-term costs. The truth is that masonry wall systems offer a level of redundancy, safety, and durability that can last for hundreds of years if given the opportunity. When you consider masonry’s performance over such extended time frames, it’s tough to find a cheaper alternative or better value out there.

How do I find a good contractor?

Masonry contractors that are members of the local provincial associations listed here are the only contractors with access to CMDC technical services. These masonry contractor members have shown their commitment to actively contribute to the advancement of our industry through CMDC. They also enjoy access to CMDC’s latest educational initiatives, up-to-date guidance on codes and standards, and regular communication opportunities with our engineering staff. CMDC strongly advises that when seeking a masonry contractor, you consider one who holds active membership in a venture partner of CMDC.

Does masonry work need an engineer?

It depends. Masonry buildings can fall under either Part 9 or Part 4 of the building code, and the design requirements vary depending on the specific characteristics of the building. While there are situations where masonry work may not necessitate an engineer, it’s essential to exercise caution when making this determination. For example, masonry veneers are often seen as purely architectural features, but there are scenarios where engineering design is necessary. Just like other aspects of building design, each new version of the building code tends to bring more elements into the domain of engineered design. If you’re uncertain about whether you need an engineer, please don’t hesitate to contact CMDC, and we can assist in assessing whether an engineer might be required.

How is the masonry industry dealing with greenhouse gas emmissions and climate change?

CMDC and our partners, such as CCMPA, invest heavily in applied research at Universities across Canada. An overview of some of these recent programs can be found here. The masonry industry’s pathway to net zero and how we plan to address climate change and emissions targets can be found here.

How long does a masonry building last?

Masonry buildings, constructed using materials, techniques, and practices that predate the existence of building codes, electricity, and even running water, have endured for hundreds, if not thousands, of years. While these historic mass wall systems differ somewhat from modern masonry systems, the ultimate result remains the same. Modern clay, concrete, or stone masonry possesses intrinsic properties that allow their lifespans to be effectively measured in centuries. Modern masonry wall systems are designed with multiple layers of redundancy and resilience. The concept of “code minimum” is somewhat foreign to the masonry industry, as we consider our buildings an integral part of Canada’s cultural fabric. While a masonry building may be affected by other materials within it that degrade over time, requiring replacement or extensive remediation, the masonry itself often remains essentially unchanged. If designed and installed in accordance with modern codes and standards, a minimum lifespan of 100 years can be expected for a masonry building.

Is masonry bad for the environment?

Masonry is a broad term that encompasses various building materials, some of which have more significant environmental impacts than others. However, at its core, masonry is connected to locally available materials, often processed through relatively straightforward manufacturing methods. While we’re progressing toward our goal of achieving net-zero, the fundamental nature of masonry has remained largely unchanged. We extract materials from the earth, such as clay, shale, and stone, and through processes that typically involve heat, we produce bricks, blocks, and mortar. The primary environmental impacts are closely associated with the manufacturing process itself.

Can masonry be built in the winter?

Masonry construction is a year-round endeavor. Projects conducted during the winter months may necessitate extra precautions, such as hoarding and heating, to meet our cold weather construction requirements. Nevertheless, it’s a common sight in many regions across Canada to witness masonry projects in progress throughout all seasons.

About the Performance of Masonry

Can I get a 2-hour fire rating from a standard 20cm concrete masonry unit?

Concrete masonry units offer various methods to attain the Fire Resistance Rating (FRR) specified in the National Building Code of Canada. Designers can discover some wall configurations directly within the building code itself, and they can also explore numerous other options through additional resources. The most commonly used approach to establish the FRR of a masonry wall system is through the equivalent thickness method, although some manufacturers also provide fire testing data directly. In any case, there are several ways to achieve a 2-hour FRR, and it’s advisable to contact your local block manufacturer or CMDC staff for further information.

How do I support the top of a firewall?

Firewalls, as defined by the National Building Code of Canada, are a distinct category of walls. They typically have specific restrictions pertaining to their integrity when integrated with combustible construction that could otherwise be structurally compromised during a fire. The functionality of a firewall is of utmost importance, as it must remain intact even if the structure on one side fails, to ensure the safety of occupants on the other side. Various methods for achieving this in the detailing of masonry firewalls are available, and we recommend reaching out to CMDC directly for guidance.

Can I get a STC rating of 50 from a 20 cm concrete masonry unit?

There are many different ways to achieve a STC rating of 50 using a variety of different masonry unit types and wall configurations. Designers can find some of these directly within the building code itself but can also find a variety of other options through other resources.

CCMPA Physical Properties of Masonry Units


Is masonry safe for earthquake prone regions?

Masonry can be designed to suite any type of seismic region of Canada. Masonry, as with all building materials, must meet the requirements set out by the National Building Code of Canada when it comes to earthquake (or other load) resistance. Specific details have been developed to customize your design for various seismic objectives, whether it involves veneer, partition walls, or multi-story load-bearing options. A skilled designer can find an efficient solution to withstand the loads mandated by the code.

Is masonry good at resisting high loads?

Masonry provides buildings with a level of protection that’s hard to match with other materials. The natural strength, resilience, and durability of brick, block, and stone materials make masonry a reliable choice. It’s been proven over time in some of our country’s most significant monuments and buildings, offering exceptional resistance to fire, moisture, pests, and even uncommon stressors like impacts, wear and tear, fires, floods, and more. Masonry construction and detailing readily stand up to these challenges. All materials must meet the minimum resistance required to support any loading specified in the building code, but masonry’s robustness and resilience that go well beyond these minimums make it an excellent choice that provides peace of mind for both owners and occupants.

How much maintenance does masonry require?

In most cases the answer is essentially none. There may be cases where after long periods of time such as 50-100 years, repointing of mortar joints could be done if there are localized issues, often due to unusual conditions, but otherwise, modern masonry construction designed by educated professionals and installed by well trained masons should expect to last for hundreds of years as we see in places around the world.

About Masonry as a Loadbearing System

Loadbearing masonry is a cost-effective, durable, customizable system with many other benefits. There is a dedicated series of pages and articles covering this topic in more detail, available here.

About Masonry Partition Walls

How tall can I build a partition wall?

The height of a partition wall depends on various factors that a well-thought-out design can accommodate. When designing partition walls under Part 4 of the National Building Code of Canada, there’s only one prescriptive height limit, which applies solely to unreinforced masonry. This limit is an effective height-to-thickness ratio (kh/t) less than 30. In reinforced masonry cases, the height of a partition wall is determined by its capacity to withstand factored loads through the design process. For technical questions related to a specific partition wall design, you can seek assistance from MASS and CMDC staff.

How far apart should my partition anchors be?

The spacing of partition anchors is determined by the factored resistance of the anchor and the factored loads acting on the anchor’s tributary masonry area. In many cases, a good starting point is to align your partition anchors with cells that contain vertical reinforcement within the wall. If the partition wall has a bond beam at the top, the anchor spacing can often be chosen for convenience in that specific scenario. CSA A370 includes non-mandatory notes that suggest horizontal support anchors typically should not exceed a spacing of 10 times the nominal wall thickness, and vertical support anchors should not typically exceed 4 times the nominal wall thickness. However, designers have the flexibility to consider other spacing limits as long as the partition is appropriately designed.

Do I need a bond beam in the top course?

In general, no, a bond beam at the top of a partition wall is not always required for walls subject to out-of-plane loads. Bond beams are often used at the top course to facilitate load transfer to partition anchors. However, this can also be achieved by locating anchors at cells where vertical reinforcement is present. In some cases, designers may also opt to provide bond beams at the course immediately below the top of the wall if it can be demonstrated that this provide sufficient strength to assure that reaction forces in the anchors can be transferred to the wall. CMDC staff can aid designers in determining how this can best be achieved.

Do I need to reinforce my walls?

The requirements for partition walls depend on various factors, including the wall’s dimensions, the factored loads it must withstand, the seismic hazard of the building, and whether the partition contains openings. Increasingly, designers are finding that reinforced masonry partition walls are a necessity in buildings across Canada. However, it’s important to note that the design of unreinforced masonry following CSA S304 is just as safe as reinforced masonry and adheres to the same limit states design requirements as reinforced masonry. So, while it’s not as common as it once was, designers can be confident that if a partition wall meets the design criteria outlined in CSA S304 for unreinforced masonry, there is no need to incur additional costs for reinforcement.

Should I tie my walls to columns?

In general, it is not advisable to connect masonry partition walls to the main structural system of the building. Masonry partition walls are designed to function independently from the primary structural framework. Specifically, the partition anchors commonly used at the top of the wall are engineered to facilitate the installation of a movement joint along the upper section of the wall. They allow for relative in-plane and axial movements while providing out-of-plane support exclusively. Tying a partition wall to a column or other structural element is likely to result in masonry cracking, and in more severe cases, it can create an infill shear wall that engages in lateral in-plane load sharing between the main structure and the partition. This situation may lead to catastrophic damage during wind or seismic events. Designers are strongly encouraged to exercise great caution when considering any type of connection that could result in the transfer of in-plane or axial loads to a non-loadbearing masonry partition wall.

What is the fire rating of a masonry partition wall?

The fire resistance rating of masonry depends on several factors, including the size of the unit, the aggregate type of the unit, the solid content of the unit, and any materials used to fill the cells of the units. In many instances, the fire resistance rating of masonry can be determined using the National Building Code of Canada equivalent thickness method of analysis, which is summarized in detail here. It’s worth noting that masonry partition walls can be designed and detailed to readily achieve fire resistance ratings exceeding 4 hours. CMDC staff are well-equipped to assist designers in navigating the available resources and design details to achieve the required fire resistance rating for any masonry wall.

What is the sound rating of a masonry partition wall?

In general, this depends on many factors such as the aggregate type of unit, the solid content of the unit, materials used to fill the cells of units, or any coverings or coating applied to the surface of walls. A wide range of different STC ratings are readily achievable with masonry alone, or in combination with other insulating/sheathing materials. CMDC staff can help designers navigate the available resources and design details that can be applied to achieve the sound resistance rating needed of any masonry wall.

Can I put openings in my partition wall?

Numerous masonry partition walls necessitate the inclusion of doorways or window openings for the convenience of occupants. Masonry construction offers a straightforward approach to creating openings due to its modular nature, which stands as a compelling advantage compared to other systems. When detailing around an opening, the designer must ensure compliance with prescriptive reinforcement requirements. It is also imperative that the masonry surrounding the opening is engineered to withstand all relevant tributary axial and out-of-plane loads.

Can I reinforce a partition wall built with 10 cm units?

Although it may seem like this is possible when considering the minimum face shell dimensions for a 10 cm concrete masonry unit in CSA A165.1, the reality is that most 10 cm units are manufactured in a manner that would prohibit vertical reinforcement and grout to pass through. This is due to the taper that many concrete masonry units possess as a byproduct of their manufacturing. Although possible to custom cut these units to better facilitate both grouting and vertical reinforcement placement, it is impractical and not at all cost effective compared to other preferable options such as opting for a larger unit size or designing the wall to resist load through horizontal bending. In general, designers should not think of 10 cm concrete masonry units as capable of being reinforced.

How far apart should I put movement joints?

The location of movement joints in partition walls are generally used to ensure that whole building loads (in-plane and axial) are not transmitted to these non-loadbearing partitions. In this sense, movement joints are typically placed along the top and sides of a partition wall to ensure no load transfer other than that of out-of-plane loads to the partition anchors. Movement joints may also be used to alleviate locations where stresses can concentrate and lead to cracking of the masonry. Depending on the wall’s function, aesthetic specifications, and the reinforcement arrangements within the walls, it may be necessary to incorporate movement joints within the wall structure. This is typically done at best practice locations, such as where openings are situated, and at regular intervals in the case of extended, uninterrupted masonry spans. A variety of resources are accessible for proper design guidance in this regard, and CMDC staff are readily available to address any questions regarding the design and positioning of movement joints.

About Masonry Veneers

How tall can my veneer go off my foundation?

When it comes to masonry veneers designed according to CSA S304 Clause 9, there isn’t a strict height limit imposed on how far they can extend above a foundation. In most cases, it’s the relative movements between the veneer and the backup structure that influence the continuous height of the veneer and whether shelf angles are needed.

Typically, the taller the continuous masonry veneer, the more significant the relative movements between the backup and veneer will be. These movements must be considered when dealing with elements that penetrate the veneer, like windows, pipes, vents, and so on. Applying a fixed limit of 11 meters to veneers designed through CSA S304 Clause 9 is not accurate. There are various design options available, and you can find design examples in our textbook that illustrate different strategies for supporting masonry veneer. These strategies may include using shelf angles at every floor level, at every second floor level, having continuous masonry above the veneer for part of the building’s height transitioning to shelf angles, or building up without shelf angles altogether.

Each approach comes with its own design requirements, cost considerations, and technical challenges, but CMDC is readily available to assist designers in selecting the right solution for their project.

Do I need shelf angles for my veneer?

Shelf angles are a means to provide intermittent support for veneers that help to break sections apart to permit differential movements. The necessity for shelf angles depends on factors like the extent of movement between the backup and veneer, the number of penetrations through both layers, and the moisture management approach used in the cavity. Sometimes, the use of shelf angles and continuous horizontal movement joints can be influenced by aesthetic considerations and architectural goals. In many cases, shelf angles may not be needed as long as all aspects of the veneer design, particularly relative movements, are carefully considered. CMDC staff can assist with any specific questions about the need for shelf angles and how to design a veneer with or without them

Where should I put movement joints?

Movement joints in veneers are typically positioned to prevent stress concentration that can lead to masonry cracking. They also serve to accommodate relative movement between the building structure and the veneer, especially around elements that connect the two, like windows and shelf angles. The placement of movement joints in veneers is often guided by best practice locations, such as near openings, and at regular intervals for extended uninterrupted masonry sections. You can find various resources explaining proper design practices, and CMDC staff are available to address any questions you have about designing and positioning movement joints.

BIA TEK18A: Accommodating the Expansion of Brickwork

How far can I corbel brick? How far can a veneer hang off a shelf angle?

Prescriptive requirements in CSA A370 will limit brick corbelling to one-third of the unit thickness, while the projection of non-loadbearing masonry supported on a shelf angle or other support is limited to the lesser of 30 mm or one-third the unit thickness. In no case should a unit be projected so that cores, cells, or other voids are visible. In special cases a designer could justify a larger corbel or projection but they would need to ensure that the stability and durability of the masonry is not compromised. CMDC staff can directly work with designers who are dealing with these specific questions.

Can I go more than 11m off the foundation?

You absolutely can!

The interpretation of an all encompassing 11 m limit as a constraint on masonry veneer design is one of the most common misinterpretations we see.

This height limit is only applicable in cases where masonry is designed in accordance with Part 9 of the National Building Code of Canada or when following the empirical design method specified in Annex F of CSA S304. Given the limited applicability of Annex F, most masonry veneers fall under the design criteria outlined in CSA S304 Clause 9, such as any of those with steel stud backup walls.

When determining the maximum allowable height for a veneer directly on the foundation, designers should take into account the impacts of differential movements and how the wall system integrates into their overall building envelope and moisture management strategy. However, they have the freedom to select any height they deem suitable, as long as it aligns with the requirements specified in CSA S304 and applicable codes. CMDC is available to assist designers in navigating these distinct requirements.

About Masonry Mortars and Grouts

Do I need to match my grout strength to my unit strength?

No, in new construction designers should specify grouts based on the requirements outlined in CSA A179. A minimum compressive strength contained in the property specification pathway for masonry grouts specifies a minimum compressive strength of 10.0 MPa or 12.5 MPa, for fine and coarse grouts, respectively, at 28 days. There are few benefits to exceed these requirements unless prism testing is being undertaken to establish a design value for masonry compressive strength, f’m.

Is 20 MPa a good minimum strength for grout?

No, in new construction designers should specify grouts based on the requirements outlined in CSA A179. A minimum compressive strength contained in the property specification pathway for masonry grouts specifies a minimum compressive strength of 10.0 MPa or 12.5 MPa, for fine and coarse grouts, respectively, at 28 days. There are few benefits to exceed these requirements unless prism testing is being undertaken to establish a design value for masonry compressive strength, f’m.

Should I be using non-shrink grout?

Grouts that contained additives or admixtures that claim to offer non-shrink properties are not necessary in masonry construction following the requirements in CSA S304 and CSA A371. The use of such materials in masonry grouts require conformance with the requirements for property specified grouts contained in CSA A179 and should only be used when assurances are provided that these additives do not have an adverse effect on the performance of the masonry. This is typically done with assemblage testing. Proportion specified grouts that are mixed with aggregates, cement, and water as laid out in CSA A179 will perform satisfactorily and have many decades of proven performance which have served as the basis for design equations in CSA S304.

Can I ever use mortar as grout?

The answer is almost always “no”, unless when specified by the designer. There are few instances where a designer may opt for using mortar as a substitute for grout, typically limited to locations where the grout is not relied upon to resist loads and reinforcement is not provided for strength or stiffness (ie. simply occupying space inside a unit below grade). Mortar performs poorly when it comes to its ability to develop reinforcement and unless heavily modified, does not typically have the flowability required to penetrate all voids in masonry nor bond properly with the units.

Do I need a mortar strength that matches the strength of the masonry unit?


A common misunderstanding is that mortar strength should somehow be tailored to the unit strength. This misconception is rooted in historic and restoration fields of masonry, especially when dealing with lower strength units, where modern mortars used to repoint these walls may be several magnitudes stiffer than the units themselves.

In restoration, mortar is typically used as the sacrificial material to prevent cracking of the units, using too strong of a mortar may cause the opposite effect. However, in new construction using modern materials and following CSA standards, this approach has no basis for consideration.

A minimum compressive strength contained in the property specification pathway for masonry mortars specifies a minimum compressive strength of 3.5 MPa or 8.5 MPa, for Type N and Type S mortars, respectively, when prepared on the job site and tested at 28 days. There are few benefits to exceed these requirements unless prism testing is being undertaken to establish a design value for masonry compressive strength, f’m.

About Masonry Tolerances and Appearance

Why do I see shadows on my masonry wall?

Shadowing is commonly created when coincidental light sources, such as spotlights positioned close to a wall surface, are used. Even minor surface variations of less than 1 mm can result in shadowing when improper lighting is employed. The simplest way to minimize unwanted shadowing on masonry is to ensure that walls are illuminated with diffused light sources or that lights are directed away from the wall’s surface. In most instances, these shadows are not a fault of the wall but rather a consequence of the lighting choices made.

What is the white, chalky substance on the surface of my masonry?

In many cases this material is a normal part of masonry construction that shows up shortly after construction is complete. It is called efflorescence and occurs when moisture contained in a unit migrates to the surface and evaporates, depositing soluble salts and minerals on the surface. Efflorescence is typical in new masonry construction and can be cleaned rather easily in most cases following proper masonry cleaning techniques. Persistent efflorescence on masonry surfaces is usually an indicator of a broader building envelope issue. When appearing in localized areas it can indicate that excess moisture is passing through the veneer. In these cases, the presence of efflorescence can be sued a powerful diagnostic tool for broader issues within the building envelope.

Why don't the head joints line up in my running bond veneer?

In cases of unreinforced masonry, particularly veneers, constructed in a running bond pattern there are no specified tolerances for head joint alignment. In contrast, masonry patterns such as stack or vertically reinforced running bond masonry have defined vertical alignment tolerances of ± 20 mm, along with a relative alignment requirement of ± 6 mm within a 3-meter span. However, when dealing with unreinforced running bond masonry, the situation differs. In a running bond pattern, maintaining precise vertical alignment of head joints becomes progressively challenging for masons as the masonry element’s height increases. Standard practice acknowledges that head joints in unreinforced masonry utilizing a running bond pattern are not necessarily aligned to a plumb line. Instead, head joint alignment often adjusts between masonry courses to accommodate permissible variations in the overall length of the masonry. These variations can result from the accepted vertical, lateral, and relative alignment tolerances for masonry elements or tolerances for non-masonry elements integrated into or adjacent to masonry junctions.

What are typical masonry tolerances to expect when looking at a mason's work?

Designers can find industry acceptable masonry tolerances of construction within CSA A371. In most applications the tolerances specified in this standard are readily achievable and will result in aesthetically pleasing and structurally sound masonry. In some cases, designers may specify tighter tolerances, exceeding those provided in CSA A371, but in all cases these should only be done with special care and must still provide the mason with an overall tolerance envelope to follow following the same style of tolerance and relative alignment envelopes found in CSA A371. If deciding to alter these values, it must be recognized that this will come at a labour premium and will fall outside what is considered to be typical masonry construction. Furthermore, tolerances listed in CSA A371 are intended for unit masonry, meaning that masonry units that do not meet the dimensional limits for unit masonry specified in the standard. While these units can often adopt many of the provisions applicable to unit masonry, designers should seek additional requirements from the manufacturer to ensure their conformance. In all cases, the use of a sample panel to establish acceptable construction practices and details is strongly recommended by CMDC.

What is a sample panel?

A sample panel is a representative section of masonry, which may be a stand alone panel or a part of the finished wall, that demonstrates the bond pattern, mortar, workmanship and overall appearance that is deemed acceptable for a masonry project. Sample panels are to be signed off in writing before work continues and will serve as the basis for which all masonry work is to be judged. A sample panel is the best way toe ensure that all parties understand what the objectives of the masonry work are to be judged against and is one of the best ways to mitigate disputes and conflicts on a job site.

CMDC strongly recommends that samples panels be used by contractors and designers where qualitative objectives, such as aesthetics, are which the final masonry project is to be judged.

Is it okay if there are units with chips in my wall?

Masonry units, and more broadly, masonry construction in general, are physical elements constructed by skilled tradespeople, but subject to physical limitations from manufacturing and installation that will always result in some level of imperfection. In the same way that concrete, steel, and wood construction all possess tolerances of construction, masonry cannot be constructed without some level of acceptable tolerances too. This extends to the individual units used in masonry construction, of which there may be thousands upon thousands of bricks or blocks used in any single project. Every masonry material accepted for use in Canadian construction according to CSA A371 will posses some predefined set of tolerances. In clay brick and concrete block, one of these tolerances acknowledges that some level of chippage should be expected in masonry units. The size and prevalence of this chippage will vary across different types of units, however, it is not possible to manufacture masonry that is completely free of any type of chip or defect. Designers should be aware that these limits do exist but that so long as units meet the standards they generally do not detract from the final appearance of masonry when viewed properly from a distance of 6 m and under diffused lighting.

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The Canada Masonry Design Centre helps members of the design community across the country by connecting them to the resources and supports they need. Contact us today and get the conversation started!

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