Masonry mortar is a binding material used in masonry work to join bricks, cinder blocks or stones. There are three basic formulas, including Portland cement blend, polymer cement mortar, and lime mortar. It is also used for repair and restoration. ASTM C270 categorizes four types of mortar based on strength and durability. Type N is the most commonly used variety.
Masonry mortar is a building material that is used as a binder in masonry work. It is used to join bricks, cinder blocks or stones and to keep them firmly in place over time. Masonry mortar starts out as a thick paste, then dries or hardens over time to form a dense material that is nearly as hard and strong as stone itself.
There are three basic formulas for creating masonry mortars. Most commonly used is a Portland cement blend, which includes Portland cement, water, and sand. Newer versions use polymers such as latex or resin to complement the natural binding agents in the concrete. Known as polymer cement mortar, this material is more durable and resistant to damage than traditional Portland cement mixes. Finally, some installers still rely on the classic lime mortar consisting of limestone, brick dust and water.
During construction, masonry mortar is spread over the top and sides of each stone. Excess material is removed before it can harden and stain the finish of the material. More grout can be added to even out the look of the structure, then tools are used to create smooth or rounded seams within the grout before it dries.
Masonry mortar is also used to repair or restore existing structures. The old mortar is chiseled away and replaced with new material in a process known as ‘pointing’ or ‘point up’. In buildings originally constructed with lime mortar, it is important to use lime-based mixes to avoid moisture problems in areas where old and new mortar mixes interact.
The American Society for Testing and Materials (ASTM) is an international organization that produces the most widely used standards for building products, including mortar. ASTM C270 “Standard Specification for Unitary Masonry Mortar” is used throughout most of the world to standardize and classify different types of mortar. According to this publication, masonry mortar can be divided into four categories, each of which is named randomly using a different letter found in the word “mason.” Each type is distinguished by its strength and durability, which is based on both the ingredients and the level of moisture contained in each blend.
Type N is the most commonly used variety and is designed for all normal above ground applications. It is the most affordable of all four types and has an average level of strength and hardness. Type S is used in lower level applications such as foundations and basements, while Type M is designed for extremely heavy loads. Type O mortar is mainly used for sealing existing masonry, but can also be used in applications subject to very cold temperatures due to its low moisture content.
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