Copyright Goodheart-Willcox Co., Inc. 304 Section 4 Construction Details wythe, allowing the joints to close as a result of an increase in size of the assemblage. In addition to accommodating movement, expansion joints also resist water penetration and air infiltration. Expansion joints should be formed as the wall is built and must be located so the structural integrity of the masonry is not compromised. Control Joint A control joint creates a plane of weakness in concrete masonry. In conjunction with reinforcement or joint reinforcement, a control joint controls the location of cracks due to volume changes resulting from shrinkage and creep. A control joint is usually a vertical opening through the concrete masonry wythe and may be formed of inelastic materials. A control joint opens rather than closes. Control joints must be located so the structural integrity of the concrete masonry is not affected. Building Expansion Joint A building expansion (isolation) joint divides a building into separate sections so stresses devel- oped in one section do not affect the integrity of the rest of the structure. The isolation joint is a through- the-building joint that allows adjoining parts of a building to move freely from one another. Construction Joint A construction joint (cold joint) is used in concrete construction where masonry work is inter- rupted. This type of joint occurs at a location suitable to terminate work, such as in the middle of a long wall, because of the limitation of scaffolding or to aid in sheltering smaller sections of work. At a predeter- mined location, the mason terminates work at a vertical plane and then continues laying brick until that section of the wall is completed. The next section of the wall will then begin at the construction joint to continue until that section is completed. Construction joints are located where they are least likely to impair the strength of the structure or building. Bond Breaks Because brick, block, and other masonry prod- ucts expand and contract differently under stress and temperature, cracks may occur due to differ- ences in the expansion and contraction rates of those materials. Bond breaks are necessary to prevent these cracks. Building paper or flashing is used to separate, or break the bond, between two surfaces of masonry materials, such as concrete block or brick. Bond breaks are used between floor slabs and foundations, because the concrete slab and founda- tion are usually under different states of stress due to loading. Bond breaks are also required when dissimilar materials come in contact with each other, such as concrete and clay masonry. Bond breaks allow each element to move somewhat inde- pendently while still providing the necessary support. A typical method of breaking the bond between walls and slabs or walls and foundations are shown in Figure 14-60. Brick Masonry Soffits A brick masonry soffit encloses a building and provides an attractive appearance. Constructing a large soffit in place often requires expensive forming and shoring. However, if only a small soffit area is involved, using a brick masonry soffit may be more efficient. Brick Industry Association Figure 14-60. Typical method of forming bond breaks in a loadbearing cavity wall. Concrete roof Insulation CMU Bond break material Brick Bond break material