How it works

Type S is typically mixed at two parts portland cement, one part hydrated lime, and nine parts sand, yielding a mortar that develops strength rapidly and resists penetration of moisture. The trade-off is reduced flexibility: type S is too rigid for historic soft-brick walls, where it can crack the brick units rather than the joints. For modern hard brick or concrete masonry units used in load-bearing applications, the higher strength is appropriate.

In chimney work, type S appears at the base of the chimney where it transitions to the foundation, in chimney chase walls that bear roof and crown loads, and in any below-grade or grade-level masonry. Above the roof line, type N is generally preferred unless the original construction used type S throughout. Mixing types within a single chimney is common, with type S below the roof and type N above.

DFW context

DFW’s expansive Blackland Prairie clay produces seasonal soil movement of two to four inches in some areas, putting lateral pressure on chimney bases. Type S mortar at the base resists that movement better than type N, and TSE technicians use type S during base tuckpointing on chimneys with documented foundation movement. Above the roof, type N remains the choice because the upper masonry needs flexibility for thermal cycling.

Related terms

• [Type N mortar](/glossary/type-n-mortar/)
• [Refractory mortar](/glossary/refractory-mortar/)
• [Tuckpointing](/glossary/tuckpointing/)
• [Repointing](/glossary/repointing/)

Sources

• ASTM C270 mortar specification
• IRC 2021, Section R607.2
• NFPA 211 (2024), Section 10.4