Pick the wrong mortar and a wall that should last 100 years cracks in five. Choosing the right brick mortar mix comes down to four letters, N, S, M, and O, each tuned to a specific load, exposure, and project type. Mason supply yards still get calls every week from homeowners who used Type S on a soft-brick repointing job and watched the original brick fail before the joint did.
- What Mortar Actually Does
- The Four Standard Mortar Types
- Cement-Lime-Sand Ratios by Type
- Type N: The All-Around Choice
- Type S: For Structure and Soil
- Type M: Below-Grade and Heavy Duty
- Type O: For Historic and Interior Work
- Mixing and Working the Mortar
- Common Mistakes to Avoid
- Frequently Asked Questions
What Mortar Actually Does
Mortar is more than glue. It distributes load, accommodates minor brick movement, sheds water, and ideally sacrifices itself before the brick does. The right mix matches the strength of the masonry units it bonds. Use mortar that is too hard against soft historic brick and the brick face spalls under stress instead of the joint cracking. Use mortar that is too weak on a load-bearing wall and the wall fails.
The Four Standard Mortar Types
ASTM C270 defines four mortars by strength and ingredients. Each has a target compressive strength and a specific cement-lime-sand ratio.
- Type N: 750 PSI. Above-grade general use. The default for chimneys, exterior walls, soft brick, and most homeowner projects.
- Type S: 1,800 PSI. Load-bearing walls, foundation walls, and areas exposed to high lateral loads like retaining walls.
- Type M: 2,500 PSI. Below-grade and high-stress applications, manholes, sewers, and heavy load foundations.
- Type O: 350 PSI. Interior non-loadbearing work and tuckpointing of soft historic brick. Rarely sold in bags, often custom-mixed.
Cement-Lime-Sand Ratios by Type
If you mix from scratch using portland cement, hydrated lime, and clean masonry sand, the proportions are by volume, not weight. These ratios come straight from ASTM C270.
- Type N: 1 part portland cement, 1 part lime, 6 parts sand.
- Type S: 2 parts portland cement, 1 part lime, 9 parts sand (often expressed as 1:1/2:4-1/2).
- Type M: 3 parts portland cement, 1 part lime, 12 parts sand (or 1:1/4:3-3/4).
- Type O: 1 part portland cement, 2 parts lime, 9 parts sand.
Most homeowners skip the from-scratch mix and buy preblended bags. Quikrete Type N (#1136), Sakrete Type S, and Spec Mix preblends are clearly labeled at any home center for $7 to $14 a 60-lb bag.
Type N: The All-Around Choice
Type N is the right answer for almost every above-grade homeowner project: brick veneer, garden walls under 4 feet tall, chimney rebuilds, and tuckpointing on most modern brick. It is strong enough to carry typical wall loads but flexible enough to accommodate freeze-thaw movement without cracking the brick face.
If you are not sure which mortar to use, Type N is rarely wrong. Coverage runs about 30 to 40 brick per 60-lb bag with standard 3/8-inch joints.
Type S: For Structure and Soil
Anywhere lateral pressure threatens the wall, retaining walls, foundation walls below grade and at grade, exterior masonry exposed to high winds or seismic loads, Type S is the standard. Its higher cement content means greater bond strength and tensile strength, but it is also less forgiving with soft units.
Block walls in northern climates often spec Type S because the higher cement content also resists freeze-thaw better. Always check local code, some jurisdictions require Type S for any structural masonry.
Type M: Below-Grade and Heavy Duty
Type M is the strongest standard mortar at 2,500 PSI. Use it for retaining walls over 4 feet, masonry foundations in contact with earth, manhole construction, and any below-grade application where compressive strength matters more than flexibility.
Be aware that Type M’s stiffness can crack softer units. Pair it only with hard, dense brick or concrete masonry units rated for the same compressive load.
Type O: For Historic and Interior Work
Old brick made before 1930 is often softer than modern mortar. Repointing 1890s brick with Type N or S can cause the brick face to spall along the joint over a few winters. Type O’s lime-rich, low-cement formula matches historic mortars and lets the joints breathe and flex.
Type O is also fine for interior partition walls and decorative non-load-bearing work. It is rarely stocked at home centers, you will usually buy it through a masonry supply yard or mix it yourself.
Mixing and Working the Mortar
Whether bagged or batched, get the consistency right. Properly mixed mortar holds a clean ridge when scooped with a trowel and slumps slowly under its own weight. Soup-thin mortar means too much water and weak bond. Stiff, crumbly mortar will not bond properly to the brick.
- Mixing time: 3 to 5 minutes minimum. Under-mixed mortar has dry pockets that fail later.
- Working time: Use within 90 minutes in mild weather, 45 minutes when above 80 degrees Fahrenheit.
- Re-tempering: Adding water once is acceptable within the working window. Twice ruins the mix.
- Temperature: Lay above 40 degrees Fahrenheit. Cold-weather laying requires heated materials and tenting.
Common Mistakes to Avoid
The biggest error is treating concrete mix and mortar mix as the same product. Concrete contains aggregate the size of pea gravel and is too coarse for thin masonry joints. Mortar uses fine masonry sand and is engineered specifically to flow into and bond joints around 3/8 inch wide.
Other frequent mistakes: using sandbox sand instead of masonry sand (different grain size and contains organic material), mixing too much at once and letting it set up, and applying mortar to dirty or wet bricks. Lightly mist very dry brick before laying so it does not pull water out of the mortar prematurely.
Frequently Asked Questions
What is the most common type of brick mortar mix?
Type N, used for almost all above-grade residential masonry, including chimneys, garden walls, and brick veneers.
Can I use mortar mix below grade?
Type S works for most light below-grade applications. Type M is the right choice for heavy retaining walls and structural foundations in contact with soil.
How long does mortar take to cure?
Initial set within 1 to 2 hours, full strength at 28 days. Keep mortar damp for the first 48 hours to prevent rapid drying cracks.
Is mortar mix the same as concrete mix?
No. Mortar uses fine sand and is designed for thin joints. Concrete contains gravel aggregate and is designed for slabs and structural pours.
What mortar should I use for repointing old brick?
Type O for pre-1930 brick. Type N for most 20th-century brick. Match the existing mortar’s strength to avoid damaging the brick face.
