Lehigh Hanson's masonry cements consist of portland or blended cement, plasticizers, and an air-entraining agent. Air-entraining agents protect mortar from freeze-thaw damage and provide additional workability. The specific components of masonry cement may vary depending on the manufacturer and local construction practices. ASTM C91 defines masonry cement by physical requirements and performance properties rather than ingredients.
Masonry cement Types N, S and M are covered by ASTM C91, Standard Specification for Masonry Cements.
Lehigh Hanson's Portland lime cement consists of portland cement and hydrated lime. The lime serves as a plasticizer. Portland lime blends in Types N, S and M are only covered by ASTM C270, Standard Specification for Mortar for Unit Masonry. This is because the two components, portland cement and lime, are each covered by their respective specifications: ASTM C150, Standard Specification for Portland Cement, and ASTM C207, Standard Specification for Hydrated Lime for Masonry Purposes.
For consistency and convenience, most portland lime blends are premixed and added to sand and water at the job site to produce mortar. However, some contractors prefer to mix all ingredients at the job site.