Masonry: 10 tips from the field

November 6, 2021

[1]By Brian E. Trimble, P.E., CDT, LEED AP, FASTM, and David Sovinski

Each project is unique, but there are some common mistakes, problems, and inefficiencies that occur on a regular basis, affecting the cost, schedule, or performance of building enclosures.

Understanding material qualities and resultant performance is the core of good masonry construction. Common misunderstandings about the basic material of masonry, clay masonry, or brick can be better understood by reading ASTM C216-19, Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale).

While there are many important requirements in this standard, studying two tables will eliminate many common issues and potentially costly mistakes. Bricks are subject to chipping. Think about the manufacturing process involving tumbling, firing, packaging, and the actual delivery. Once the brick gets to a jobsite, it may be handled several times before actually being placed into service in a wall. Potential for chipping is high, and ASTM C216-19 recognizes this. Figure 1 details chippage allowances.

Minimizing how often a brick is handled is important not only for chippage, but also for the productivity of a mason contractor, since time spent on transportation logistics can quickly add up. Dan Schiffer, former president of Schiffer Mason Contractors even commented, “I am not always a mason contractor, but often a transportation contractor”.

Tip 1: Understand brick crack allowances

When viewing a FBS brick wall for allowable cracks, the general requirement is to stand 6 m (20 ft) away in diffused lighting and check for visible cracks or imperfections. More stringent standards for FBX brick allow for 4.5-m (15-ft) viewing distance. A close examination will likely show some imperfections. This may be fine with the design intent, since as one architect explained, “that is part of the romance of brick…”

Chippage allowances, as per ASTM C216-19, Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale).

Tip 2: Realize bricks have dimensional tolerances

Table 2 of ASTM C216-19 (see Figure 2) shows the dimensional tolerances of brick.

A trained mason will space out the brick in a wall and make up the differential with wider or narrower head joints, resulting in an esthetically pleasing appearance while minimizing excessively large mortar joints.

Including detailed requirements for a mockup of the masonry wall system will help define expectations. The mockup should include, but not be limited to, all masonry accessories, showing how they interact with other materials, the brick, including range of colour, size, shape, and texture, and finally, the expected workmanship. Imagine inspecting a commercial project with 100,000 bricks, which would have nearly a mile-and-a-half of mortar joints. Measuring each brick or mortar joint is more difficult than assessing the overall appearance by comparing to a masonry mockup.

Concrete masonry is typically specified by referring to ASTM C90-16a, Standard Specification for Loadbearing Concrete Masonry Units. The viewing distance for imperfections is again 6 m under diffused lighting. Dimensional variance is +/– 3 mm (0.125 in.) from the specified dimensions. Again, comparing the installed product to an approved mockup is an effective method of determining quality.

Tip 3: Use modular dimensioning

Modular design seems intuitive and natural, and masonry units lend themselves to the concept. Concrete masonry, for example, while available in many sizes and shapes, often is specified with a nominal 200-mm (8-in.) high x 405-mm (16-in.) long face dimension, with varying widths. One can save time and money by designing both height and length to this modular dimension when spacing openings. A concrete masonry unit (CMU) is one of the best bargains in construction, and a skilled bricklayer can install them rapidly. The cost rises quickly, however, when extra cuts and layout time are involved. In Figure 3 (page 32), the wall is off module and a bricklayer needs to measure and mark each cut, send the block to a saw, and have the extra expense of laying more units. In this case, each concrete block around the perimeter of the opening needed to be cut. If the opening could have been shifted only an inch or two, then there would have been a steady spacing of half and whole blocks. Add this up over many openings and costs can escalate.

A good concept used by estimators is the rule of 200-mm heights. If the foot dimension is an even number, then the height to stay on module is either the even foot or the even foot plus 200 mm. If the foot dimension is an odd number, the height to stay on module is the foot dimension plus 100 mm (4 in.). Any other height and costs increase.

This concept works for brick as well. On a recent dormitory project in Ohio, a plan review noted window dimensions were slightly off module. Shifting them fractionally preserved the design intent, but saved more than $10,000 on the bid cost for reduced cutting of brick.

Dimensional tolerances of brick according to ASTM C216-19.

Tip 4: Locate movement joints on the drawings

Some of the more popular questions the author’s firm (the International Masonry Institute [IMI]) receives revolve around movement control. Concrete products, including concrete masonry, tend to shrink as they cure and lose moisture. Clay masonry expands with moisture and experiences dimensional changes for thermal expansion as well. It is helpful to recognize that and note on the drawings, locations, and provisions for movement control. Placing this only in a specification can lead to confusion and potential cracks in the masonry system. Control joints should be placed at various intervals for concrete masonry, as it tends to shrink. Clay masonry should have expansion joints to allow small growth of the brick.

According to the Masonry Society (TMS) 402/602, Building Code Requirements and Specification for Masonry Structures, the masonry code referenced by the International Building Code (IBC), the coefficient of thermal expansion for clay masonry is 7.2 x 10-6 mm/mm/C (0.000004 in./in./F), which works out to roughly a 13 mm (0.5 in.) of growth over a 30-m (100-ft) span with a 38 C (100 F) temperature difference.

Tip 5: The mason contractor should not locate the movement joints

While IMI and other groups offer advice on standard spacing for control and expansion joints, and review specific projects to make recommendations for movement joint location, the ultimate responsibility is with the designer of record. Decades ago, the masonry building code understood this need. The code now contains provisions requiring the designer, not a contractor or other source, to locate and detail provisions for movement control in masonry. While trained mason contractors are an asset to the project, they may not know the design intent or how the walls were structurally designed.

Properly designed masonry works with the adjacent materials as a system to control moisture penetration, vapour, airflow, and energy transfer. Most problems in the enclosure occur where two dissimilar materials meet.

In this project, the wall is off module and a bricklayer needs to measure and mark each cut, send the block to a saw and bear the extra expense of laying more units, thereby increasing project cost.

Tip 6: Pay extra attention to where dissimilar materials meet

It is important to take great care where dissimilar materials requiring installation by different trades meet. Specifications and contracts should carefully state responsibilities.

Putting masonry units together as a system is the next step toward high performance. Masonry walls fall into the general categories of barrier, cavity, or drainage and rainscreen walls, which are a refinement of the cavity wall system. The most common issue with any masonry wall system is water penetration. Building professionals tend to assume moisture intrusion is a result of wind-driven rain, but designers should pay attention to other sources, including rising damp, vapour diffusion, and airborne moisture that moves due to differences in temperature and pressure. With the rise in the use of air and moisture control systems and layers, there is an increase in moisture problems due to uninformed or incorrect placement of the air and vapour barriers, or unintended consequences of trapping moisture or vapour, and location of the dewpoint.

It sounds counterintuitive, but in a cavity or drainage wall one assumes moisture will find its way into the cavity. Brick themselves do not leak, but water can find a way into the system.

The first dissimilar material to investigate is the actual mortar joint. A mortar joint that is both tooled and compressed during installation is the first line of defense against moisture penetration. Figure 4 features a sample of mason tools used for tooling and compressing mortar joints.

Small hairline cracks in mortar joints are to be expected and should be no cause for alarm unless they grow to exceed roughly 1.5 mm (0.0625 in.). In that case, it should be looked at as a possible source of moisture, and the problem should be addressed in maintenance.

Assuming some amount of moisture will enter the masonry cavity, the strategy is for moisture to drain down the back of the veneer to flashing and weep vents. Flashing materials, and their installation, are the source of many long and detailed articles, so for this discussion, the author only wants to point out some common mistakes.

First, laps can cause leaking. Since most flashing systems require a lap from one section to another, this is a natural place for problems to occur. It is advisable to check the lap size and whether appropriate sealants were used. Most manufacturers will recommend anywhere from 50 to 150 mm (2 to 6 in.) for the lap. Based on jobsite experience, IMI recommends a minimum lap of 150 mm. This reduces the possibility of moisture travelling underneath the lap and also gives additional room for the installer to have some tolerance.

Mason tools employed for tooling and compressing mortar joints.

Check all flashings to see if there are penetrations. In many cases, the flashing is installed with the backup concrete masonry, with the intention to install the brick veneer later. This leaves some vulnerable types of flashing exposed to other trades prior to installation of the brick veneer. This can be addressed by either changing the sequencing or installing the flashing later with the brick veneer using a termination bar (Figure 5).

When using a termination bar, it is advisable to insist on a sealant bead across the top of the bar to resist water draining behind the flashing. Trade co-ordination in the masonry enclosure is critical.

Windows, doors, and changes in materials from brick to concrete, stone, glass, or metal are all potential areas for leaks. When two trades meet, there is always the possibility for a huge sealant joint due to tolerances or just poor co-ordination. This leads to another common issue: the size of the drainage plane, cavity, or air space itself. With various tolerances in the construction industry among steel, wood, concrete, and the masonry itself, one needs some room in the cavity between the back of the brick and the face of the backup material. Building codes call for a 25-mm (1-in.) minimum cavity dimension. While this may seem generous, consider various tolerances and the possibility for mortar droppings or other construction debris to fill a cavity. The author’s firm recommends a 50-mm air space independent of any insulation in the cavity.

A 50-mm air space has positive effects, including:

• promoting airflow through the cavity, a first principle towards rainscreen construction; and

• allowing for some level of mortar droppings.

A good cavity should be “clean, but not pristine.” Craftworkers trained by the International Masonry Training and Education Foundation (IMTEF) are taught to minimize droppings through good workmanship, but also to have a full head and bed joint.

The flashing can be installed along with the brick veneer by using a termination bar.

Tip 7: Minimize efflorescence and other unsightly deposits and stains

The most common call on this topic to the author’s firm concerns efflorescence, more accurately termed a deposit than a stain (Figure 6). Sometimes called new building bloom, efflorescence often shows up at the time a contractor is trying to collect retainage and the construction team is trying to turn a job over to an owner. For efflorescence to occur, three factors need to happen:

1) Water needs to enter the masonry system;

2) There needs to be a source of soluble salts; and

3) These salts need to migrate to the surface of the brick through capillary action and are left behind when water evaporates.

Finding the source of efflorescence can be as simple as finding the source of water penetration. A less simple answer is to sample the salts to find the actual physical source. New building bloom is usually caused by excessive water in the masonry wall during construction. One should always specify covering the open cavity wall during construction. When new building bloom is the source of efflorescence, it will often disappear with normal weathering. If efflorescence continually shows up on the wall, the source of moisture should be found and repaired. If not, salts may not only deposit on the face of the wall, but also occur as subflorescence beneath the face of the brick, leading to spalling of the masonry face. Cleaning efflorescence follows the common-sense rule of first using a mild detergent with a scrub brush. If this is insufficient, proceed to chemical cleaners under strict conformance with the manufacturer’s directions. Often chemical cleaners can make the problem worse. A common mistake is to hasten the process by either not wetting a wall, if called for, using an improperly diluted cleaning solution, or leaving the solution on the wall for too long a period. All of these can lead to masonry ‘burning,’ often noticeable as a sandy mortar joint.

Lime runs typically occur at a small hole, opening, or hairline crack in the face of the brick masonry (Figure 7). Lime runs are often mistaken for efflorescence. Lime runs are caused by repeated water flow through mortar joints. The deposits are often thicker and harder to remove than efflorescence. Consult with a trusted professional to use proper cleaning techniques.

While well-written specifications and other contract documents are absolutely critical to define roles, responsibilities, and expectations, good communications is another method to ensure success.

Efflorescence is usually caused by excessive water in the masonry wall during construction.

Tip 8: Use pre-job meetings and mockups to optimize communication

Pre-job meetings with trades and ongoing site co-ordination meetings are critical to the success of a project. Allow trades to speak freely while respecting their contractual relationships and they will often point out some of the trade co-ordination and schedule/sequencing issues that can result in poor performance. It is easy to skip these meetings while trying to maintain a schedule and productivity, or when a trade is inactive on a job, but regular attendance and participation in the process will help reduce future problems.

Thinking of the mockup as part of the communications plan also manages expectations of workmanship during construction.

Tip 9: Training makes a difference

“…it is pretty generally admitted that few of them were to be trusted within reach of a trowel and a pile of bricks.” – PG Wodehouse

IMI and IMTEF train thousands of craftworkers annually in apprenticeship and journeyworker upgrade courses. These programs include certifications in various skills and trades, as well as safety, welding, and many other specialty courses. Some or all of these can be included in project or model specifications to help ensure the best quality installation from craftworkers trained in specific skill sets.

Lime runs typically occur at a small hole, opening, or hairline crack in the face of the brick masonry. They are caused by repeated water flow through mortar joints.

Tip 10: Innovate

Today’s bricklayer is a building enclosure installer who maintains the skills and understanding to successfully place the various control layers managing air, moisture, vapour and thermal control, along with structure and finish, giving a single source solution and higher quality installation to the finished product.

Looking ahead, technological advances in design, manufacturing, and installation will accelerate the changes in how services are delivered to the marketplace.

The masonry industry came together in 2012 to form an initiative called BIM for Masonry, funding development of many tools, software, and training to educate contractors and support the architecture/engineering (A/E) community. Visit for more information.

The masonry industry is developing mason assists and robotic supports. As early as 1992, IMI worked with the U.S. Army Corps of Engineers to develop the Mechanically Assisted Masons Aid (MAMA) that assisted a mason in lifting heavy units. Today, we see similar products, and development of exoskeletons that improve and extend the work life of a masonry craftworker.


In an era of not only rapid change, but also an increase in the rate of evolution, collaboration between all parties in the building process will deliver the best product to the end-user.

[9]Brian Trimble is director of industry development and technical services at the International Masonry Institute (IMI). He is a licensed professional engineer in Pennsylvania and Virginia with more than 25 years’ experience in the masonry industry assisting design professionals with masonry structures. He is a Fellow of ASTM International and frequently lectures on masonry subjects. Trimble has an architectural engineering degree from Penn State University.

[10]David Sovinski is a retired masonry industry professional, formerly serving as national director of industry development at the International Masonry Institute’s (IMI). His experience includes masonry project manager, estimator, and architecture and technology teacher at Indiana University Purdue University Indianapolis (IUPUI). Sovinski has a degree in building construction from Purdue University.

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