Type S vs Type N Mortar: Choose for the Wall, Not Just Strength

Type S mortar has higher compressive strength and generally higher flexural bond strength; Type N is the normal choice for many above-grade brickwork applications. Neither is automatically better. For existing masonry, compatibility with the brick or stone and the original mortar comes before choosing the stronger mix. The Brick Industry Association recommends the lowest-strength mortar that meets the project requirements. BIA selection guidance

This comparison uses ASTM C270 terminology for unit masonry, with U.S. brick-industry selection guidance. Structural specifications and applicable local rules take precedence over a general selection guide.

The differences at a glance

Property	Type S	Type N
Minimum average compressive strength at 28 days under laboratory property testing	1,800 psi (12.4 MPa)	750 psi (5.2 MPa)
Common cement–lime–sand recipe, by volume	1 : ½ : 4½, also written 2 : 1 : 9	1 : 1 : 6
General character	Higher compressive and flexural bond strength	Good bonding capabilities and workability
Typical selection direction	Stronger applications, including some reinforced or loadbearing exterior walls	Normal brickwork, including most anchored brick veneer

The strength benchmarks and permitted cement–lime proportions are set out in BIA Technical Note 8; the application guidance comes from Technical Note 8B.

The psi figures are not guaranteed strengths of the mortar in your wall. ASTM C270 provides alternative proportion and property specifications. The property route qualifies laboratory-prepared mortar at a controlled flow; field-sampled mortar strength cannot be used directly to judge compliance with those laboratory requirements. A Type S label does not mean a wall can carry 1,800 psi. ASTM C270 scope and abstract

What changes in the mix—and in use

The familiar recipes above are for mortar made with Portland cement, masonry-grade hydrated lime and sand, not every product sold as Type S or Type N.

Under the cement–lime proportion specification summarized by BIA, each type uses one volume of cement, but:

• Type S: lime is more than ¼ and up to ½ volume.
• Type N: lime is more than ½ and up to 1¼ volumes.
• Sand is 2½–3 times the combined volume of cement and lime, measured damp and loose.

Thus, 1:½:4½ and 1:1:6 are common recipes within permitted ranges, not the only possible formulations. Measure by volume, not by assuming equal bag weights. BIA proportion requirements

Portland cement contributes strength, early setting and durability. Lime contributes workability, water retention and some ability to accommodate slight movement. In comparable cement–lime mixes, Type N’s larger lime proportion therefore changes more than the strength number: it helps the mortar spread, maintain contact with the units and retain mixing water against their suction. The brick’s absorption matters too; greater water retention is not always preferable for low-absorption units. BIA mortar properties and brick–mortar compatibility guidance

That water retention while laying is different from vapor permeability after curing. A strength classification alone does not establish permeability: NPS notes that even hard historic lime mortars can remain highly permeable. NPS Preservation Brief 2

When to choose Type N—and when Type S fits

The following recommendations concern new brickwork, not automatic replacements for historic mortar.

Choose Type N for normal above-grade brickwork where the design permits it. BIA recommends it for most anchored brick veneer, exterior non-loadbearing walls, interior partitions, and exterior brick parapets and chimneys. Exterior exposure by itself does not require Type S. BIA application recommendations

Choose Type S where the design needs its higher strength or bond performance. BIA recommends it for above-grade reinforced or loadbearing exterior brick walls and identifies high-wind and high-seismic applications as cases that may need stronger mortar. BIA selection guidance

The binder system matters too: masonry-cement mortar is not automatically equivalent in structural bond performance to non-air-entrained cement–lime or mortar-cement mortar of the same type. Follow the specified type and binder, rather than substituting by letter alone. BIA binder and bond guidance

For foundations and retaining walls, do not reduce the decision to “below grade means S.” BIA lists Type M as recommended and Type S as an alternate for these applications. Loads, exposure and the wall design determine the choice; mortar strength alone does not establish wall adequacy. BIA use-based selection table

Adhered stone veneer has separate requirements for its coats, bonding bed and joints; use the layer-specific veneer mortar guide rather than transferring anchored-brick-veneer advice to it.

For repointing, either type may be wrong

Type N is weaker than Type S, but that does not make it automatically compatible with historic masonry. A soft-brick wall originally built in lime-rich mortar may require a more carefully matched repair mortar than either standard mix.

The National Park Service calls for replacement mortar that is softer and more vapor-permeable than the masonry units, and as soft or softer and as permeable as the historic mortar. Excessively strong mortar can concentrate movement-related stress in the units; an unsuitable, less-permeable joint can also restrict drying and contribute to salt-related damage. NPS Preservation Brief 2

For newer brickwork, Type N may be suitable for repointing. For older work, assess sound original mortar and the units before specifying a replacement. BIA repointing guidance See matching mortar before repointing for the repair decision—not just the bag selection.

Check what the bag contains

A complete mortar mix already contains sand; for example, QUIKRETE’s Type N Mortar Mix contains masonry cement and graded sand and needs only water. A masonry cement or mortar cement binder needs the specified sand added. Do not apply the cement–lime recipes above to a proprietary binder or add extra cement to a finished mix in an attempt to “upgrade” it. Follow the product formulation and project specification. BIA material and proportion guidance

Also, Type S hydrated lime is not Type S mortar. It is an ingredient classification and can be used in Type N cement–lime mortar. Confirm the finished mortar type, binder system and mixing instructions before buying. BIA hydrated-lime guidance