What is the maximum allowable bedjoint thickness between masonry units?

• A. 5/8 inch
• B. 3/8 inch
• C. 3/4 inch
• D. 1/4 inch

Answer: (C)

Bed joints are the horizontal mortar layers that bond masonry units together. Keeping them thin helps maximize contact and bond strength while reducing the chance of shrinkage cracks and water infiltration. The maximum thickness allowed for a bed joint is three-quarters of an inch. This upper limit allows for small irregularities in the masonry while still providing enough mortar to develop a solid bond and transfer loads effectively. If a bed joint gets thicker than that, bond quality declines and the masonry becomes more prone to voids, cracking, and moisture movement. The smaller options are typically used when joints are kept deliberately thin, but they do not set the upper limit the way three-quarters of an inch does.