26 Ways to Prevent Cracks in Brickwork
Total Page：16
File Type：pdf, Size：1020Kb
| THE BUILDING ENVELOPE | By Brian E. Trimble, PE, CDT, LEED AP, FASTM; James A. Tann, FASTM; and Charles (Chip) Clark, AIA, PE, LEED AP 26 WAYS PHOTOS: BRICK INDUSTRY ASSOCIATION PHOTOS: BRICK INDUSTRY TO PREVENT CRACKS IN BRICKWORK Brian E. Trimble, PE, CDT, LEED AP, FASTM, former Senior Director of Engineering Services and Archi- tectural Outreach at the Brick Industry Association, Photo (left) shows is Director of Industry Development, International correct placement Masonry Institute. James A. Tann, FASTM, Past of expansion joints President of the Brick Institute of America–Mid East in a university build- Region and former Member of the Board of Directors ing. Inset shows of ASTM International, is Director of Technical Ser- damage from the vices, Belden Brick Co. Charles (Chip) Clark, AIA, PE, lack of an expansion LEED AP, is Vice President of Engineering Services, joint at a junction. the Brick Industry Association. hanges in temperature or LEARNING OBJECTIVES moisture can wreak havoc on After reading this article, you should be able to: building materials, and brick is + LIST several physical characteristics and properties of brick that can no exception. Elastic deforma- affect brickwork installation and longevity. tion due to loads, creep, or changes in volume can cause + DESCRIBE the proper location of horizontal and vertical expansion movement, which can crack joints in brickwork according to Brick Industry Association Technical Notes 18 and 18A. your project's lovely brickwork. ThereC are two basic ways to avoid + DISCUSS the use of a “lipped” brick course when a large horizontal cracks in brick work: 1) minimize the expansion joint is called for. movement, or 2) accommodate move- + DELINEATE the technical factors for locating expansion joints in thin ment between materials and assem- brick applications according to Brick Industry Association Technical blies, through a system of movement Note 28C. joints that allow for some give in your brickwork. 50 | BUILDING DESIGN+CONSTRUCTION | March/April 2021 THE BASICS OF EXPANSION JOINTS Projected Moisture Expansion. Fired Brick vs. Time IN BRICKWORK 1. Be aware that brick can change slightly in vol- ume, depending on the age and color of the brick, the direction the wall faces, and the temperature at installation. 2. Assume that bricks will increase slightly in size over their life. This is due primarily to moisture expansion and, says coauthor Brian E. Trimble, "it's part of how bricks are made." Brick Industry Association (BIA) Technical Note 18 has helpful formulas for calculating the movement of brick walls. 3. Use expansion joints in your brickwork. Expansion joints separate brick masonry into seg- ments to prevent cracking caused by temperature change, moisture expansion, elastic deformation, settlement, or creep. They can be horizontal or vertical. Most of the expan- VERTICAL EXPANSION JOINTS 4. Don’t confuse expansion joints with control sion of fired brick due joints. According to BIA Technical Note 18A, the to moisture occurs term "control joint" is used in reference to con- in the first year of installation (above). crete or concrete masonry construction. A "build- Graphic (right) shows ing expansion joint" is a through-the-building joint various methods for that separates a building into discrete sections installing vertical expansion joints, as to relieve stress. A "construction joint" (or "cold recommended by the joint") is used primarily in concrete work when Brick Industry Asso- construction is interrupted. ciation. Source: BIA 5. Form the expansion joint correctly, 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. 6. Make sure all expansion joint materials extend through the full thickness of the wythe to keep mortar and other debris from clogging the elastic deformation due to loads, shrinkage and joint and block water from penetrating the joint as creep of mortar, construction tolerances, and wall much as possible. orientation. "There's something of an art to get- 7. Don’t use fiberboard or similar materials in ting this right," says Trimble. expansion joints; they are not compressible. 10. Don’t go more than 20 feet without a verti- 8. Don’t allow mortar, ties, or wire reinforcement cal expansion joint for brickwork in a veneer or to extend into or bridge the expansion joint, as cavity wall. For brickwork without openings, place these materials can restrict movement and undo expansion joints no more than 25 feet apart. the benefit of the expansion joint. "This is a well-accepted rule of thumb in the industry," says coauthor James Tann. HOW TO APPLY VERTICAL EXPANSION JOINTS 11. Don’t leave it up to the masons to position 9. Be aware that the positioning and spacing the expansion joints. "The design professional of expansion joints in brickwork will vary from should take responsibility for determining the structure to structure, depending on a variety of placement and spacing of joints," says Trimble. factors: the amount of expected movement, the 12. Prioritize expansion joint placement in areas size of the expansion joint, the compressibility of of high stress concentration, where cracking the expansion joint materials, restraint conditions, is most likely to occur. Starting at a corner and BDCuniversity.com | BUILDING DESIGN+CONSTRUCTION | 51 | THE BUILDING ENVELOPE | EXPANSION JOINT WITH LIPPED BRICK Sealant in Reglet Continuous Insulation BRIAN TRIMBLE COURTESY BRICK INDUSTRY ASSOCIATION BRICK INDUSTRY Flashing Protection on Bold Heads Flashing Full-Height Shim Shelf Angle Weep Sealant and Backer Rod Min. 1/4 inch (6mm) Thick Compressible Material Graphic illustrates the correct method for locat- placing joints at the typical spacing around the expansion joints are typically needed if the brick ing an expansion joint building perimeter is not recommended. wythe is supported on a shelf angle attached in a lipped brick course, which is used to allow Tip: Begin placement at material transitions, junc- to the frame or used as infill within the frame. movement while reduc- tions, and offsets before placing at an outside Placing horizontal expansion joints below shelf ing the potential nega- corner. By placing expansion joints at these high- angles provides space for vertical expansion of tive aesthetic impact of the expansion joint. priority areas first, only a few expansion joints, if the brickwork below and deformation of the shelf any, will be required to meet the maximum spac- angle and the structure to which it is attached." ing recommendations. For step-by-step details, 15. Provide horizontal expansion joints under refer to BIA Technical Note 18A, page 7. each shelf angle in structures that support the 13. Place vertical expansion joints at or near brick wythe on shelf angles. corners (outside and inside), offsets and set- 16. Remove temporary shims that may have been backs, openings, wall intersections, changes in used to support the shelf angle during construc- wall heights, and parapets. For corners, place tion. an expansion joint within at least 10 feet of the 17. Consider using a "lipped" brick course in corner on at least one of the two walls. cases where you see the need for a large horizon- 14. Place expansion joints at the junction of tal expansion joint. Lipped bricks allow movement walls with different environmental or climatic while reducing the potential negative aesthetic exposures or support conditions. impact of the joint. Tip: Use expansion joints to separate adjacent Tip: To avoid breakage, the height and depth of brick walls of different heights to avoid cracking the lipped portion of the brick should be at least caused by differential movement. The joint can a half-inch (13mm). be placed at the interior corner or, if appropriate, Caution: For quality assurance, have your lipped a foot or so away from the corner to provide a brick made by your brick manufacturer. "Masons masonry bonded corner for stability. can saw cut a lip brick from a standard unit, but Note: Wall ties must be in place to properly support this is not as precise as what manufacturers the brick wythes adjacent to the interior corner. can do. Overcutting, often performed when field fabricating lipped brick, can cause the cut units to ADDRESSING HORIZONTAL EXPANSION fail," warns Tann. JOINTS IN BRICKWORK 18. Be sure to evaluate the movement toler- According to BIA Technical Note 18A, "Horizontal ances of adjacent materials, including the 52 | BUILDING DESIGN+CONSTRUCTION | March/April 2021 building frame itself. This is especially true for an anchored brick veneer with a wood frame backing THIN BRICK MOVEMENT JOINTS when its height exceeds 30 feet. Additional detail- ON CMU BACKING ing may be required to address the shrinkage of the wood. Thin Brick ASSOCIATION BRICK INDUSTRY For more information, refer to BIA Brick Brief: “Designing Anchored Brick Veneer Above 30 feet Thinset Mortar or Adhesive with a Backing of Wood Framing” (https://bit. ly/3bmvXhP). Sealant and 19. Don’t allow contact at any time between the Backer Rod lipped brick and the brickwork below the shelf angle or between the lip of the brick and the shelf angle. ADDITIONAL FACTORS TO CONSIDER 20. Consider ways to make expansion joints less noticeable, especially on long, flat walls. Control Joint 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 THIN BRICK MOVEMENT JOINTS joint, or by using special-shaped bricks. ON STUD BACKING 21. Try to locate expansion joints at inside cor- ners, where they are less noticeable. Thin Brick ASSOCIATION BRICK INDUSTRY 22. Don’t hide expansion joints behind down- spouts or other key building elements, unless you want to get a lot of nasty calls from the build- Thickset Mortar Bed ing's maintenance department.