SPELLING OUT STRENGTH
Most masonry cements are preblended, ready to be mixed with sand and water at the job site. Premixed masonry cements offer a convenient, consistent and uniform performance. An alternative to premixed masonry cements is to mix all the individual ingredients – cement, lime, sand and water – at the job site.
The American Society for Testing and Materials (ASTM) designates both mortars and the masonry cement used to produce them by types, which are primarily based on strength. Traditionally, alternating letters of the words "mason work" became the letters used for five types of mortar: MaSoN wOrK, with Type M being the strongest and Type K the weakest. ASTM now designates three types of mortar: Type M, Type S and Type N. Types O and K are no longer common in construction and are used primarily for restoration of historic masonry structures. Type N is for general use in most mortar and stucco applications. Types M and S are specified when higher strength is required in load-bearing or below-grade walls.