What is the requirement for the thickness of masonry unit bed joints for the second course?

The requirement for the thickness of masonry unit bed joints for the second course is established to ensure stability and proper adhesion between the masonry units. The standard thickness for these joints, which is set to accommodate both the need for strength and the capabilities of mortar application techniques, is 3/8 inch. This thickness allows for an effective bond as well as adequate spacing to accommodate potential expansion and contraction of materials.

A bed joint that is too thin may not allow sufficient mortar to fill the irregularities of the units, leading to weak points in the masonry structure. Conversely, a joint that is too thick can lead to excessive mortar usage, increased weight, and may negatively affect the aesthetics of the finished product. Thus, the 3/8 inch thickness strikes the right balance for achieving a durable and visually appealing masonry wall, making this choice the correct answer in the context of established masonry practice.