Mortar
Definition
Mortar is a workable paste made from cement, sand, water, and sometimes lime, used to bond bricks, blocks, and stone in masonry construction. Unlike concrete, mortar does not contain coarse aggregate and is designed to be softer than the units it bonds. Mortar types are classified by compressive strength: Type M (2,500 PSI, below-grade), Type S (1,800 PSI, general structural), Type N (750 PSI, above-grade non-load-bearing), and Type O (350 PSI, interior non-load-bearing). A standard 80 lb bag of mortar mix covers approximately 12โ15 standard bricks or 5โ6 concrete blocks.
Why is Mortar Important?
For homeowners, contractors, and DIY builders across the United States, understanding Mortar is essential to accurate material estimation and cost planning. Whether you are pouring a concrete driveway, framing a deck, or calculating roofing materials, mastering this concept helps prevent costly over-ordering or project delays from material shortages.
Our free construction calculators leverage this concept to provide instant, accurate estimates โ saving hours of manual measurement and arithmetic while ensuring your project stays on budget.
What is Mortar?
Mortar is a workable paste composed of cement, fine sand, water, and sometimes lime or other additives, used to bond masonry units (bricks, concrete blocks, and stone) together and fill the gaps between them. Unlike concrete, mortar does not contain coarse aggregate and is intentionally designed to be softer than the units it bonds โ this allows the mortar joints to absorb movement and stress rather than cracking the bricks or blocks.
Mortar Types (ASTM C270)
| Type | Compressive Strength | Bond Strength | Best Use |
|---|---|---|---|
| Type M | 2,500 PSI | Good | Below-grade: foundations, retaining walls, heavy loads |
| Type S | 1,800 PSI | Best | Structural masonry, at or below grade, high wind/seismic |
| Type N | 750 PSI | Moderate | Above-grade: chimneys, exterior veneer, non-load walls |
| Type O | 350 PSI | Low | Interior non-load bearing, tuck-pointing historic buildings |
| Type K | 75 PSI | Very low | Historic restoration only (very soft, matches old lime mortar) |
Mortar Coverage Estimates
| Masonry Unit | Joint Size | Coverage per 80 lb Bag |
|---|---|---|
| Standard brick (3โ " ร 2ยผ" ร 8") | โ " | 30โ35 bricks |
| Standard brick | ยฝ" | 25โ28 bricks |
| Concrete block (8" ร 8" ร 16") | โ " | 10โ12 blocks |
| Concrete block | ยฝ" | 8โ10 blocks |
| Natural stone (fieldstone) | ยฝ"โยพ" | 10โ15 sq ft |
Mortar vs. Concrete vs. Grout
| Property | Mortar | Concrete | Grout (masonry) |
|---|---|---|---|
| Aggregate | Fine sand only | Sand + coarse gravel/stone | Fine sand (or pea gravel) |
| Strength | 350โ2,500 PSI | 2,500โ6,000+ PSI | 2,000โ3,000 PSI |
| Consistency | Thick paste (trowelable) | Thick (pourable/moldable) | Fluid (pourable into cavities) |
| Purpose | Bond masonry units | Structural โ slabs, footings | Fill block cores/bond rebar |
| Sold As | Pre-mixed bags (60/80 lb) | Ready-mix or bags | Pre-mixed bags or site-mixed |
Mixing Tips
- Mix to a peanut-butter consistency โ mortar should hold its shape when squeezed but not crumble
- Use clean, potable water; contaminated water weakens the bond
- Mix only what you can use in 90 minutes โ mortar begins to set and loses workability after that
- Do not add water to re-temper mortar that has begun to set; discard and mix fresh
- In hot weather (85ยฐF+), dampen masonry units before laying to prevent them from absorbing water from the mortar
- In cold weather (below 40ยฐF), use special winterized mortar or heated water and protect work from freezing for 24โ48 hours