Brick masonry is one of our most widely used building materials and has been used to construct building façades for thousands of years. Because brick is manufactured from natural materials, and with firing processes that produce a nonuniform temperature distribution across a cube of brick, brick masonry from the same plant, product line, and even from the same batch and production run will have variations in color and, occasionally, surface texture.
These visual differences must be accommodated in a building's design and construction. Architects and engineers engaged in preservation and rehabilitation work have long struggled with the problem of having to match the color and surface texture of historic brick masonry.
But problems related to “brick color” and “brick texture” also affect new commercial construction, mainly in the form of undesirable patterns in an otherwise uniform distribution of brick colors and textures.
We summarize some traditional brick blending practices and ways that have been successful in achieving uniform distribution of brick masonry.
Why blend brick?
The appearance of brick masonry is largely defined by the size, color, and surface texture of the units, along with the configuration, color, and texture of the mortar joints. Brick should be blended or mixed in a wall to obtain an evenly distributed, or approximately random distribution of brick colors. When brick are not adequately blended, accumulations of like colors, repeating patterns, or unintended discernible geometric patterns occur. Architects and building owners usually object to such patterns.
Another frequent aesthetic problem is adjacent internally uniform fields of brick with very similar, but subtly different appearance. These appearance issues are not easily discernible when viewed up close, such as from a scaffold. But they become prominently apparent when viewed from a distance, often when the masonry has been cleaned and scaffolding is removed near the end of a project.
Hence, to avoid disputes, finger-pointing, nonacceptance of the work, or costly removal and replacement of areas of brick during the punchlist phase, or after removal of the scaffold, the brick must be blended thoroughly before construction.
Brick manufacturers understand the necessity for blending brick colors and intermix brick during the packing process to achieve a uniform color distribution. Skilled masons also recognize the need for blending brick and use traditional procedures, such as unpacking cubes of brick at a 45-degree angle, mixing brick from different cubes on the scaffold, and using judgment when placing individual brick into a wall.
Even though the requirement to blend brick appears to be a well-recognized practice, there is no known industry standard that defines how to blend brick masonry to achieve a uniform appearance or random distribution. After reviewing industry publications and discussions with practitioners in brick masonry design and construction, we determined that the terms “blend” or “blending” in the brick industry mean “evenly or randomly distributed, sometimes according to a specified ratio, without discernible repeating patterns or unusual accumulations of the same colors, and with the goal of achieving uniform appearance.”
While this is a practical working definition, it does not establish a procedure for producing such a blend. Where the appearance of a wall is critical or the skill and experience of the installer is limited, the design professional may have to specify the blending process.
From plant to jobsite
To view the process used to blend brick of various colors, we visited a manufacturing plant of a prominent Pennsylvania brick manufacturer to observe the blending and packaging process.
Most of the brick produced at the plant we visited are “flashed” brick. These have a dark finish caused by the burning of iron-oxide in the clay, with a darker color distribution around the top of the brick stacks where the kiln is hottest. Due to the variations in surface color between the top and bottom, and between the interior and exterior of the brick stacks, flashed bricks are blended to produce a random distribution of colors.
At the plant, flashed brick are pre-mixed before they are strapped and packaged in brick cubes for inventory or delivery. During this premixing process, 10 workers, each working off their individual palette of brick that comes straight from the kiln, work in front of a rotating carousel containing many open shelves. Each worker places one row of brick on the shelf in front of him (for modular brick, roughly 10 per row) before the carousel turns and the next worker lays the next course on top of it. For modular brick, the shelves can hold 11 courses (or about 110 total brick).
As each worker picks brick from his palette and stacks it on the shelf, he removes brick from the palette at a 45-degree angle. This mixes bricks from the palette's interior and exterior that may have color differences due to flashing or from uneven temperature distributions between the interior and exterior of the stack. The shelves of brick are then strapped and assembled into cubes where each strap has been pre-blended in this manner.
When a cube is delivered to a construction site or to a precast panel manufacturer, an instruction sheet advises the mason to follow the same 45-degree angle rule when tearing down the preblended cube and laying the brick in a wall. The procedure provides a small amount of blending at each step of the process, from the manufacturing plant to installation.
Manufacturers are reluctant to interrupt their production and packaging process to accommodate custom blending projects, or blending certain proportions of various brick colors. But the process used in the plant we visited can be adapted to intermix proportioned amounts of different brick colors as defined by the architect's design.
Thus, intermixing different brick colors to create a custom blend generally takes place in a yard and requires the manual disassembly and reassembly of different brick cubes which were previously internally blended at the factory. This process of custom blending among different cubes of brick at the construction site is labor-intensive and costly, and requires skill and experience.
Still, this blending of brick, both in the manufacturing plant and in the field, is critical to obtain a uniform color distribution because the multistep process introduces some degree of intermixing at every step. Problems occur when blending was not performed or was left to the initiative of the brick mason.
Blending problems also occur on precast panels with thin brick veneer. The laborers typically placing the thin brick sections in a precast mold are not able to view and judge the appearance of a panel until it is complete. In their defense, uniform mixing of brick from different cubes cannot be reasonably performed given the space restrictions and schedule pressures of a jobsite or precast production facility. The best way to avoid these problems is to perform a multistep blending process before installation.
For projects with a range of brick colors or where a blend has been specified, review the blending procedure with the installer as part of the pre-installation conference and mockup. Factory blending, using a process similar to the process used at the factory we visited, is necessary for any brick masonry.
Additional blending, using a process similar to the factory blending and including the deconstruction, intermixing, and reconstruction of brick cubes, is required to produce custom brick blends incorporating several different colors. Because of the substantial effort and additional construction costs associated with this process, the blend procedure should be explicitly included in the project specifications to ensure a level playing field for bidders.
Requiring proper blending procedures is particularly important on new construction projects or during the production of brick-clad precast panels where schedule pressures or access restrictions allow neither methodical, deliberate mixing of the brick onsite, nor a critical aesthetic evaluation of the masonry in place, and from a distance. The blending procedure must be worked out in advance of general construction, its results evaluated, and appearance expectations defined using full size sample panels.
A carefully conceived and implemented brick blending process, review of sample brick masonry panels, and continuous review of brick blending procedures and the appearance of the finished product, will go a long way toward avoiding unpleasant and costly appearance problems.
Niklas W. Vigener, P.E., LEED AP, is a senior principal, and Philip Frederick is a staff I engineer at Simpson Gumpertz & Heger Inc., a national engineering firm that designs, investigates, and rehabilitates structures and building enclosures. Visitwww.sgh.com;firstname.lastname@example.org@sgh.com.