by 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 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 the 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…”
Tip 2: Realize bricks have dimensional tolerances
Table 2 of ASTM C216-19 (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 aesthetically 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 the masonry accessories, that show how they interact with other materials, the brick, including range of color, 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 (1/8 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, 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.