I have seen many architects specify expansion joint fillers for vertical expansion joints and expansion joints beneath shelf angles. What is the purpose of this expansion joint filler?

Expansion joint filler is typically placed in the joints to prevent mortar from squeezing from the bed joints or head joints and bridging the expansion joint. In the case of vertical expansion joints, you can use a strip of rigid insulation that is cut to the width of the joint and projects out beyond the face of the masonry. This insulation is then removed after the masonry sets up. This creates an open joint that can be easily inspected to confirm that the joint is not blocked. When you use foam fillers, it is still possible that mortar may bridge the expansion joint where the foam filler is discontinuous or where the foam filler was compressed under the pressure of extruded mortar. The presence of the foam filler will also make inspection of the expansion joint slightly more difficult.

In the case of horizontal expansion joints, I prefer using foam joint filler pads adhered to the underside of the shelf angle. Using a rigid material that will be removed may interfere with the installation of units on the shelf angle. If lipped brick is used beneath the shelf angle to reduce the size of the expansion joint, a foam pad is the only way I know to prevent this joint from being filled with mortar. Because it is not possible to inspect the joint in this situation, it becomes very important to inspect the foam pads adhered to the bottom of the angle before the masonry is installed. The foam pads must be continuous without gaps between adjacent sections.