Brick is the smallest dimension it will be in its long service life when it leaves the kiln. As it is exposed to moisture from a variety of sources including the air, wet mortar, rain and condensation, it will naturally expand since it is a clay product. Temperature will also cause brick to expand and contract. Consequently, it is important to incorporate expansion joints into brickwork to accommodate this movement. Expansion joints should be located where stresses or cracks are likely to develop in brickwork. Prime candidates for expansion joints include long expanses of walls, corners, offsets, setbacks, and parapets. Expansion joints should also be located below shelf angles to account for vertical expansion of brick. When accent bands of other materials such as precast or concrete masonry units are included in a wall, it may be prudent to include a bond break or slip joint between the two dissimilar materials if their coefficients of expansion are significantly different. Bond breaks are created by embedding a smooth sheet such as flashing materials in the mortar bed which allow the materials to move independent of each other. When determining where expansion joints should be placed, it may be necessary to calculate the amount of expansion anticipated. This can be done by knowing the coefficients of expansion of the brickwork and the parameters of its environment. For additional information on expansion joints, see Technical Notes 18 and 18A.