Changes in temperature or moisture can wreak havoc on building materials, and brick is no exception. Elastic deformation due to loads, creep, or changes in volume can cause movement, which can crack your project's lovely brickwork.
There are two basic ways to avoid cracks in masonry elements (for the purposes of this article, we'll stick to bricks): 1) minimize the movement or 2) accommodate movement between materials and assemblies, through a system of movement joints that allow for some give in your brickwork.
For expert advice on this problem we turned to Brian Trimble, senior director of engineering services and architectural outreach at the Brick Industry Association, Reston, Va., and James Tann, president of the Brick Institute of America - Mid East Region, Canton, Ohio. We also relied heavily on the Brick Industry Association's Technical Notes 18 ("Volume Changes - Analysis and Effects of Movement") and 18A ("Accommodating Expansion of Brickwork").
THE BASICS OF EXPANSION JOINTS
DO appreciate that brick can change slightly in volume, depending on the age and color of the brick, the direction the wall faces, and the temperature at installation.
DO assume bricks will increase slightly in size over their life. This is due primarily to moisture expansion and, says Trimble, "It's part of how bricks are made." There are helpful formulas to calculate the movement of brick walls (see Technical Note 18).
DO employ expansion joints in your brickwork. Expansion joints separate brick masonry into segments to prevent cracking caused by temperature change, moisture expansion, elastic deformation, settlement, or creep. They can be horizontal or vertical.
DON'T confuse expansion joints with control joints. According to Technical Note 18A, the term "control joint" is used in reference to concrete or concrete masonry construction. There's also a "building expansion joint," a through-the-building joint that separates a building into discrete sections to relieve stress, while a "construction joint" (or "cold joint") is used primarily in concrete work when construction is interrupted.
DO form the expansion joint by leaving a continuous unobstructed opening through the brick wythe and filling it with a highly compressible material, preferably premolded foam or neoprene pad. A backer rod and sealant are used out front to weatherproof the joint (Figure 1).
DO make sure all expansion joint materials extend through the full thickness of the wythe to keep mortar and other debris from clogging the joint and to keep water from penetrating the joint as much as possible.
DON'T use fiberboard or similar materials in expansion joints; they are not compressible.
DON'T allow mortar, ties, or wire reinforcement to extend into or bridge the expansion joint, as these can restrict movement and undo the benefit of the expansion joint.
APPLYING VERTICAL EXPANSION JOINTS
DO be aware that the positioning and spacing of expansion joints in brickwork will vary from structure to structure, depending on a variety of factors: the amount of expected movement, the size of the expansion joint, the compressibility of the expansion joint materials, restraint conditions, elastic deformation due to loads, shrinkage and creep of mortar, construction tolerances, and wall orientation. "There's something of an art to getting this right," says Trimble.
DON'T go more than 25 feet without a vertical expansion joint for brickwork in a veneer or cavity wall without openings, such as windows. "This is a well-accepted rule of thumb in the industry," says Tann. Tip: To derive the optimal expansion joint spacing for your project, consult the formulas in Technical Notes 18 (page 1) and 18A (page 3).
DON'T leave it up to the masons to locate the expansion joints. "The design professional should take responsibility for determining the placement and spacing of joints," says Trimble.
DO place vertical expansion joints at corners, offsets and setbacks, openings, wall intersections, changes in wall heights, parapets, and, of course, along long walls following BIA's recommendations.
DO place expansion joints at the junction of walls with different environmental or climatic exposures or support conditions. Tip: Use expansion joints to separate adjacent brick walls of different heights to avoid cracking caused by differential movement. The joint can be placed at the interior corner or, if appropriate, a foot or so away from the corner to provide a masonry bonded corner for stability. Wall ties must be in place to properly support the brick wythes adjacent to the interior corner.
ATTENDING TO HORIZONTAL EXPANSION JOINTS
According to Technical Note 18A, "Horizontal expansion joints are typically needed if the brick wythe is supported on a shelf angle attached to the frame or used as infill within the frame. Placing horizontal expansion joints below shelf angles provides space for vertical expansion of the brickwork below and deformation of the shelf angle and the structure to which it is attached."
DO provide horizontal expansion joints under each shelf angle in structures that support the brick wythe on shelf angles.
DO remove temporary shims that may have been used to support the shelf angle during construction.
DO consider using a "lipped" brick course in cases where you see the need for a large horizontal expansion joint. Lipped bricks (see Figure 3) allow movement while reducing the potential negative aesthetic impact of the joint. Tip: To avoid breakage, the height and depth of the lipped portion of the brick should be at least a half-inch (13 mm). Caution: For quality assurance, have your lipped brick made by your brick manufacturer. "Masons can saw cut a lip brick from a standard unit, but this is not as precise as what manufacturers can do. Overcutting, often performed when field fabricating lipped brick, can cause the cut units to fail," warns Tann.
DO take into consideration the movement tolerances of adjacent materials, including the building frame itself.
DON'T allow contact at any time between the lipped brick and the brickwork below the shelf angle or between the lip of the brick and the shelf angle.
OTHER DETAILS TO CONSIDER
DO consider ways to make expansion joints less noticeable, especially on long, flat walls. Tip: Try using architectural features such as quoins, recessed panels of brickwork, or a change in bond pattern to reduce any negative effect. Or you might go so far as to call attention to the expansion joint by recessing the brickwork at the joint, or by using special-shaped bricks.
DO try to locate expansion joints at inside corners, where they are less noticeable.
DON'T hide expansion joints behind downspouts or other key building elements, unless you want to get a lot of nasty calls from the building's maintenance department.
DON'T tooth expansion joints to follow the masonry bond pattern. It makes it harder to keep debris out of the joint during construction, debris that can interfere with the proper movement of the joint.
DO download Technical Notes 18 and 18A (gobrick.com/html/frmset_thnt.htm) for more detailed advice. Tip: Use this article and the tech notes as the basis for a lunch-and-learn discussion in your office.