Section 2304 addresses masonry assembly. Mortar is composed of cement, sand, and water, with proportions establishing different mortar types. Type N (1:3 cement:sand) is general-purpose mortar. Type S (1:2.25) is higher strength for high-rise buildings. Type M (1:2.5) is highest strength for below-grade use. Joints must be filled completely to provide water resistance and structural connection. Joint thickness is typically 3/8 inch, with vertical joints raked (removed) in some applications for appearance. Mortar reflow where fresh mortar is compressed into joints removes air pockets. Curing mortar must be protected from drying too quickly or being rained on in the first 48 hours.