What are soaps in masonry walls and when are they used?

The term "soap" is often used to describe masonry units cut to reduce their depth. The Brick Industry Association (BIA) defines soaps as "A masonry unit of normal face dimensions having a nominal 2-inch. thickness." In actual construction, I have seen soaps cut down to a depth of 1 inch.

They are often used where a reduction in depth is needed to conceal obstructions within the masonry wall. Soaps are used in front of bolts, flanges of embedded lintel beams, or to cover the projecting edge of the slab.

Soaps can present problems in wall systems. They are very difficult to anchor because of their reduced depth. The problem is particularly prevalent if there are multiple adjacent courses of soaps in a wall. Also, because soap units are positioned at the exterior face of the wall, compressive loads within the exterior wythe must be transferred through these soaps. Masonry loads within the soaps do not coincide with the loads in the center of the wall. This situation can result in buckling. Soaps within masonry veneers should be avoided.

I have also heard the term soap used to describe units cut to reduce their height. The use of units with reduced height should not impact the structural stability of the wall or negatively impact durability.