What is the required measurement for masonry mortar joints from the first concrete masonry unit (CMU) to the foundation?

Masonry mortar joints are crucial in ensuring the structural integrity and stability of a masonry wall. The required measurement for mortar joints, particularly from the first concrete masonry unit (CMU) to the foundation, is generally specified to be 1/4 inch. This measurement allows for proper adhesion between the CMU and the foundation, providing adequate space for the mortar to fill in and bond well without being too thin or too thick.

Using a 1/4 inch joint also helps to facilitate the proper flow of moisture and air, which is vital for the long-term performance of the masonry. Joint size can affect the overall performance of the wall, including its resistance to cracking and its structural capacities. Properly formatted joints at this specified size contribute to the overall aesthetics and capability of the masonry work.

Other measurements, such as 1/8 inch, 3/8 inch, and 1/2 inch, may be used in different scenarios or for specific types of construction but do not meet the standard requirements for the thickness of mortar joints at the base of a CMU wall.