Mortar is the material between bricks—a mix of cementitious binder, sand, and water that locks the units together and seals the joints.
Mortar, In Plain Words
Brickwork needs a glue that doesn’t look like glue. That glue is mortar. It starts as a workable paste, fills bed and head joints, then hardens into a tight bond. Good mortar carries loads, cushions slight movement, and helps shed rain. It also sets the visual tone, since joint width and color frame every brick.
Modern mortar falls under standards such as ASTM C270, which sorts mixes by type and baseline strength. The letters can feel cryptic, yet they’re handy once you know the gist.
Common Mortar Types And Where They Shine
| Type | Typical 28-Day Strength* | Typical Uses |
|---|---|---|
| M | ~2,500 psi | Foundations, retaining walls, harsh exposure |
| S | ~1,800 psi | Structural walls, high wind or seismic zones, below grade |
| N | ~750 psi | General above-grade work, veneers, everyday brickwork |
| O | ~350 psi | Interior, patching, gentle restoration |
| K | ~75 psi | Specialty historic repointing only |
*Strengths reflect property-spec minima and long-standing guidance, not a promise of field results. Pick the gentlest type that still meets load and exposure needs.
Trade groups suggest choosing the lowest strength that still does the job. Stronger isn’t always better; too-stiff mixes can push stresses into the brick itself. For historic walls, softer lime-rich blends often match the old work best. See the NPS Preservation Brief 2 for repointing practice, and Brick Industry Association’s Technical Notes 8B for mortar selection.
What’s The Material Between Brick Called—Mortar, Grout, Or Concrete?
People swap these words, yet they don’t serve the same job. Mortar bonds units. Grout fills cores, cells, or voids and flows like a milkshake. Concrete forms slabs, beams, and footings with coarse stone in the mix. If you’re laying brick, you want mortar. If you’re filling a reinforced cell, you want grout. If you’re making a footing, you want concrete. Same family, different roles.
What Mortar Is Made Of
Four parts matter: a cementitious binder, clean sand, water, and sometimes lime or polymer. The binder is usually portland cement, a blended cement, masonry cement, or mortar cement. Lime brings workability and better bond; it also adds a bit of self-healing through micro-recrystallization over time. Sand sets the texture and controls shrinkage. Water activates hydration and makes the paste workable. Pigments can fine-tune color when matched with a consistent sand.
In plain terms, engineers describe mortar as cement paste with fine aggregate, while grout is a wetter mix meant to flow into spaces and concrete is a heavier mix that includes coarse stone. That simple trio keeps project roles clear and helps you choose the right bag for the task at hand.
Mix Proportion Shortcuts You Can Trust
ASTM proportion specs leave room for fine tuning, yet a few classic by-volume blends keep projects on track:
- Type N: 1 part portland cement, 1 part lime, 6 parts sand (1:1:6)
- Type S: 1 part portland cement, 1/2 part lime, 4.5 parts sand (1:1/2:4.5)
- Type M: 1 part portland cement, 1/4 part lime, 3 parts sand (1:1/4:3)
- Type O: 1 part portland cement, 2 parts lime, 9 parts sand (1:2:9)
Those ratios are a starting point. Sand grading, brick absorption, and weather all nudge the water demand and workability. Aim for a creamy, cohesive feel that holds a line on the trowel without slumping.
How Mortar Gets Placed
Masons spread a full bed, butter the head joint, press the brick home, and tap to line and level. Joints get compacted, then tooled when thumbprint hard. That timing seals the face and sheds water. Wheat-thin slurries, “slushed” head joints, or deep furrows invite leaks. Full joints and tight tooling pay off.
Color, Texture, And The Look Of The Wall
Small choices swing the whole façade. Sand color shifts the hue. Pigment brings consistency, yet batch control and tool timing still rule the final shade. A slightly rough sand leaves a grainy look; a finer sand reads smoother. Joint width also changes the rhythm. Narrow joints show more brick face; wider joints amplify the grid.
Strength Isn’t The Only Measure
Bond matters as much as numbers on a lab chart. A mix that spreads easily and wets the brick makes a larger contact area. That “extent of bond” keeps rain out and limits cracking. Over-stiff mortar can starve the bond, especially with low-absorption brick. When in doubt, build a small panel, test the workflow, and adjust the lime or sand before running the whole wall.
Picking The Right Type For Common Jobs
Veneers And Garden Walls
Type N is the go-to for most above-grade work. It finishes cleanly, bonds well, and has enough flex for seasonal movement. In windy or high-seismic regions, Type S adds reserve without turning the wall into a rock-hard wedge.
Foundations, Piers, And Steps
Below grade and high-load areas call for Type S or Type M. Drainage and flashing still matter. Mortar strength doesn’t replace basic moisture control like positive slope, weeps, and sound waterproofing.
Historic Repointing
Older walls often need a gentler touch. Lime-rich Type O, or a custom repair mortar per historic specs, helps protect soft brick. Hard repairs trapped in soft masonry lead to spalls and edge loss. Match color, sand, and tooling so the patch blends in.
Workability Tweaks That Help
Use clean, well-graded sand. Pre-wet high-absorption brick or raise the lime within limits to retain water. Keep batches small; aim to work mortar within a couple of hours. Retemper with a light splash if the mix tightens, but toss it once set begins. In cold weather, protect materials from freezing and keep fresh work covered.
Curing And Weather Smarts
Fresh joints need a calm window. Shade the wall in hot sun. Windbreaks cut rapid drying. Light misting helps in arid air, while tarps keep pounding rain off until initial set. In frost, use heated water, warm sand, and protective enclosures. Never lay on icy units. Good curing locks in color and bond.
Masonry Myths That Waste Time
- “More cement makes stronger walls.” Past a point, it just makes the mix brittle and less forgiving.
- “Any sand will do.” Dirty or gap-graded sand weakens the joint and stains the face.
- “Tooling can wait.” Miss the thumbprint window and the surface won’t seal as well.
- “Plug a leak with surface sealer.” Most leaks start at voids or ledges. Fix the joint first.
Frequently Mixed-Up Terms
Pointing, Repointing, And Tuckpointing
Pointing is the act of finishing fresh joints on new work. Repointing means removing failed mortar and packing fresh mortar into the joint. Tuckpointing is a style move: a thin, often white fillet set into a pressed groove to mimic crisp joints.
Thinset And Tile Grout
Thinset is a polymer-modified bonding mortar used under tile, not between bricks. Tile grout fills the gaps between tiles and can be cement-based, epoxy, or urethane. Neither replaces brick mortar in a wall.
Field Checks Before You Mix
- Confirm exposure: freeze-thaw cycles, splash zones, soil contact, and de-icing salts change the game.
- Read the brick’s absorption. Extreme high or low IRA calls for tweaks to lime and water.
- Match the joint profile used elsewhere on the wall.
- Keep sand consistent from batch to batch, especially on colored work.
Safe, Sound Practice
Follow the bag label or mix design that meets code, wear eye and skin protection, and keep wash water out of drains. Lime and cement are caustic when wet. Store materials off the ground and under cover. Stack units safely, set up stable scaffolds, and keep fresh work sheltered from rain and frost.
Keep a clean wash bucket, fresh rags, and a stiff brush on hand, and pre-stage mockups so the crew can match the approved sample. Always.
Joint Profiles And Water Shedding
Joint shape affects durability and looks. Concave and V joints compress the surface and drain water fast. Flush joints read flat yet work well when neatly compacted. Raked or struck profiles can look crisp in dry climates, but the ledge can hold water and dirt in wet zones.
| Joint Profile | Where It’s Common | Weather Edge |
|---|---|---|
| Concave | Modern veneers, many exteriors | Strong seal and runoff |
| Vee | Face brick with tight lines | Compacts well; drains |
| Flush | Interior or protected walls | Good when well tooled |
| Raked | Accent work, dry settings | Can catch water and debris |
| Weather Struck | Traditional façades | Sheds water when pitched |
Quick Reference: Choosing A Mortar Type
Use this short list when you’re sizing up a job:
- Need everyday versatility? Pick Type N.
- Expect lateral loads or below-grade splash? Step up to Type S.
- Need brute compressive strength? Use Type M, with drainage dialed in.
- Fixing soft, old brick? Reach for Type O or a repair-grade mix matched to the wall.
Brick Joint Takeaways
Masonry lives or dies at the joints. Call the material mortar. Choose the type for the loads and the weather, not bragging rights. Pack joints full, tool them at the right moment, and pick a profile that sheds water. Keep sand and color stable, and test a small panel when looks matter. If the wall is historic, favor a softer repair that plays nice with old brick. Do those basics well and the bricks will carry their share without complaint.