Type S is stronger than Type N (typical strengths of 1,800 psi and 750 psi), but for repointing, stronger is not better. The National Park Service says repointing mortar must be softer than the brick and no harder than the original mortar. The Brick Industry Association recommends Type N for normal use. For older masonry, the NPS points toward softer, lime-rich mixes. The right choice depends on your wall, so ask your mason why.
Type N vs type S mortar: which is right for your brick? Type S is stronger, Type N is softer, and for repointing the rule isn't "pick the strongest." It is to match the wall. The mortar should be softer than the brick and no harder than the original mortar.
What the letters mean
ASTM C270 sorts mortar into types by strength, from strongest to softest: Type M (typical strength about 2,500 psi), Type S (1,800), Type N (750), Type O (350) and Type K (75). The letters come from the phrase "MaSoN wOrK," using every other letter. More lime makes the mortar softer and more vapor permeable (National Park Service).
So the real gap between N and S is big: Type S is typically more than twice as strong as Type N. Those numbers describe the mortar, not your brick.
Why stronger isn't better when repointing
The NPS is direct on this. New mortar must be softer, meaning lower compressive strength, and more vapor permeable than the brick, and no harder than the historic mortar. It calls the assumption that hard or high-strength mortar is better a common error (National Park Service). The joint is the sacrificial element: stress should be relieved by the mortar, not the brick (National Park Service).
When mortar is stronger and less permeable than the brick, moisture and salts move out through the brick instead, and the face can spall (National Park Service). That is the failure behind the mortar mistake that ruins old brick.
So where does Type N fit, and where does Type S?
- Type N. The Brick Industry Association recommends Type N for normal use, including most veneer, and says to select the mortar type with the lowest compressive strength that meets the requirements (BIA). For brick walls of unknown strength, going lower, not higher, is the safer instinct.
- Type S. It is stronger, and the sources we rely on don't tell us when it is appropriate for repointing. We can't make that call from here. A mason has to judge it against your actual brick.
- Type O and softer. For historic masonry, the NPS points to lime-rich mixes: Type O (1:2:9) or Type K (1:3:11) or lime-sand (National Park Service). The numbers are proportions of cement, lime and sand.
The BIA note is aimed at modern brick buildings and the NPS note at historic ones, so which applies depends on what you own (BIA). We won't tell you your brick is soft or hard without seeing it, and neither should anyone on the phone.
The usual mortar problem on older Chicago buildings isn't a wrong letter on a bag. It is a crew using one hard, fast mix on every job because that is what is on the truck. Ask what mortar they use, why it is right for this wall, and whether they will match it to the old mortar. If the answer is "we always use Type S," follow up.
Questions to ask your mason
- What mortar type, and why for this brick?
- How does it compare in strength to the old mortar and the brick?
- Is it lime-rich? What are the proportions?
- Do you do a test panel before the full wall?
- How does the color match, and is it sampled dry?
The mortar type is one piece of a bigger job. Our tuckpointing mistakes article covers the others, and if your building has limestone, see tuckpointing a greystone. When you want a mason to look at the wall, our tuckpointing crew can. The Chicago tuckpointing guide covers the rest.
Common questions
Neither is automatically better. The NPS says repointing mortar must be softer than the brick and no harder than the original mortar. Type N is softer than Type S, and the BIA recommends it for normal use. A mason should choose based on your actual wall.
Typical strengths are about 750 psi for Type N and 1,800 psi for Type S under ASTM C270, so Type S is stronger. Those numbers describe the mortar, not your brick, and stronger is not better for repointing.
Type O is a softer, lime-richer ASTM mortar type, with a typical strength of about 350 psi. For historic masonry the NPS points to lime-rich mixes like Type O. Ask your mason whether it suits your wall.
Sources
- National Park Service: Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings (PDF)
- Brick Industry Association: Technical Note 8: Mortars for Brickwork (PDF)
- Brick Industry Association: Technical Note 8B: Mortars for Brickwork, Selection and Quality Assurance (PDF)
Facts last checked: October 7, 2026.
This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.