How do I determine what mortar Type to specify?


For new construction, ASTM C270 “Standard Specification for Mortar for Unit Masonry”, defines three mortar Types: N, S, and M, listed from lower to higher compressive strengths. Within the masonry industry, a widely accepted rule of thumb is to use Type N mortar for new construction unless there is a structural or durability reason to use a higher strength mortar. For veneer, Type N mortar will often be the best choice. Higher compressive strength mortar may be required for structural masonry, below-grade masonry, or masonry in high seismic regions.

In its non-mandatory appendices, ASTM C270 offers additional guidance on selecting the appropriate mortar Type for every project. Appendix X.1 relates the type of structural member and its location (above or below grade) to the preferred mortar Type.


The decision to utilize this information is not within the purview of the MIM, and persons making use of this information do so at their own risk.  MIM makes no representation or warranties, expressed or implied, with respect to the accuracy or suitability of this information.  MIM and its members disclaim liability for damages of any kind, including any special, indirect, incidental, or consequential damages, which may result from the use of this information.  This information is not to be interpreted as indicating compliance with, or waiver of, any provision of any applicable building code, ordinance, standard or law