All masonry walls will move, primarily due to changes in temperature and moisture content. Additional movement might occur from structural concrete frame moisture loss or creep, and elastic deformation. Restraining these movements may cause stress cracks to develop in the wall. The type of movement will depend upon materials, construction, and wall configuration. The primary movement in masonry wall con-struction is thermal expansion in clay masonry and shrinkage in concrete masonry.
ACCOMODATING MASONRY MOVEMENT
Brick masonry will typically expand due to changes in temperature and exposure to the sun. The south and west elevations of a building are always warmer than the other elevations due to the constant exposure of the sun. This will cause the brickwork to expand.
Concrete masonry, like most cast concrete, will shrink from water loss due to initial drying. This condition causes all concrete masonry units to shrink.
There typically are two types of masonry movement joints for concrete masonry and brick masonry con-struction. One joint will accommodate thermal movement in brickwork and the other joint will accommodate movement shrinkage in concrete masonry.
EXPANSION JOINT
An expansion joint is required to be constructed into the brick wythe to segment the brickwork, subsequent-ly accommodating the thermal movement of the brick wall (photo #1). This should result in a crack free brick wall.
Spacing
Each brick masonry structure should be independently and thoroughly examined to determine expansion joint placement. The recommended spacing of expansion joints for brick veneer can be determined by a formula developed by the Brick Industry Association (BIA). The formula is as follows:
Se = Spacing between expansion joints
Wj = Width of expansion, typically 3/8 in. to ½ in.
eJ = Percent compressibility of expansion joint material (least of sealant)
Se = Wj eJ
0.09
For example, if the width of the joint is ½ inch, the following spacing can be determined.
Se = (0.5 in.) (50) = 278 in. or approximately 23 ft.
0.09
Masonry Movement Joints
photo #1
An expansion joint detail is required to accommodate horizon-tal expansion. The expansion joint must be free of all non-compressible materials to allow for the compression of the joint. A compressible neoprene pad or foam backer rod should be placed in the joint. The compressibility of the filler should be a minimum of 50%. The expansion joint material should terminate approximately ½ in. to ¾ in. from the exterior of the wall and be filled with sealant. Also, all joint reinforce-ment must be discontinuous at the joint (Figure 1).
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