
BY DANIEL GREEN
Retired Technical Services Manager, National Cement
MASONRY TECH TOPIC:
Mortar Types & MaSoN wOrK
Additional Resources
It seemed that A-1 carried a connotation of “best”, A-2 being 2nd best, and so on down to D. Naturally, this is not the case, as each type of mortar is intended for a specific use and no single type of mortar should be perceived as “best” for all purposes. With that, our MaSoN wOrK designations were created.
ASTM C270, Standard Specification for Unit Masonry, now includes only four types of mortar: M, S, N, and O. Type K is no longer specified. Choosing the mortar type: No single type of mortar is suited for all applications. The architect or engineer should specify the mortar that best meets project requirements. A good rule of thumb is to use the mortar with the lowest compressive strength required for the masonry feature.
Type M

Type S

Type N
Type O
Type K
Sometimes it may be specified for restoration of historic or “ancient” buildings or structures that require a mix that is not significantly stronger than the surrounding masonry work. Type K mortar compressive strength is about 75 psi. *Use masonry sand conforming to ASTM C144, Aggregates for Masonry Mortar. Add sufficient water to obtain desired mortar consistency. Mix 3-5 minutes after all of the ingredients are in the mixer. Workmanship, unit suction, mixing, curing and other variables affect the overall masonry quality.
Finally, and perhaps needless to say, this article merely touches on the highlights of mortar type selection, proportioning, and mixing. For additional information, and to name only a few, I’ll offer additional reference sources below.
*Use masonry sand conforming to ASTM C144, Aggregates for Masonry Mortar. Add sufficient water to obtain desired mortar consistency. Mix 3-5 minutes after all of the ingredients are in the mixer. Workmanship, unit suction, mixing, curing and other variables affect the overall masonry quality.