Mortar binds the masonry units together. Commonly made from a mixture of Portland Cement and lime, sand and water, mortar mixes are usually specified for in the Contract Documents for a project. There are mortar systems that are produced offsite and delivered to the jobsite (Ready-Mixed Mortars), but most mortar gets mixed in the field. Due to the field mixing of mortar, it's important the mortar ingredients and mix be consistent throughout the project. While this responsibility typically falls to the Masonry Contractor, the Construction Supervisor should notice if the mixing process seems to proceed in a quality fashion. If ingredients are stored such that foreign elements become mixed into the mortar, if the measuring process seems haphazard from one batch to the next, or if the consistency of the mortar seems to vary between batches, the Construction Supervisor may head off future problems by noticing these issues and discussing with the Masonry Contractor. The Construction Supervisor can't catch every problem on a job site, but can pay attention to best quality practices and develop the habit of noticing where future problems are likely to arise.
Mortars types are typically Type M, S, N or O. A basic understanding of these mortar types is helpful. All mix quantities given below are volume proportions (as opposed to weight proportions).
Type M mortar is the highest strength (2500 psi average compressive strength at 28 days) and is often used for below grade structures such as foundations walls and storm water structures. It has typical proportions being 1 part Portland Cement, 1/4 part lime and 6 parts sand.
Type S mortar is the next highest in strength (1,800 psi average compressive strength at 28 days) and is the general purpose high strength mortar. It tends to be the highest cost of the mortar mixes and has proportions of 1 part Portland Cement, 1/2 part lime and 4 1/2 parts sand. Most reinforced masonry walls will use Type S mortar and it's also specified for many other uses.
Type N mortar is a medium strength mortar (750 psi average compressive strength at 28 days) and tends to be used for above grade walls in moderate wind areas. The workability of Type N mortar is quite high due to the higher proportion of lime in the mix. Typical mix quantities are 1 part Portland Cement, 1 part lime and 6 parts sand. Type N and Type M mortars are lower cost than Type S mortar.
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