of excessive moisture. Many building codes do not allow Type O mortar for construction. However,
some local building codes allow Type O to be used for load-bearing walls of solid blocks when the
compressive stresses do not exceed 100 pounds per square inch. Before using this type mortar, check
local building codes.
1-14. Type S. Type S mortar is composed of 1 part cement, 1/2 part lime, and 4 1/2 parts sand. It is a
very good general-purpose mortar used in above-grade exteriors that are exposed to severe weathering.
Type S is also used in interiors and all load-bearing structures unless only Type M is specified. Type M
and S are usually interchangeable.