Mortar Calculator

How to Calculate Mortar for a Masonry Project?

Mortar quantity depends on the wall area, the masonry unit size, and the mortar joint thickness. For standard modular bricks with 3/8-inch joints, each 80-pound bag of mortar mix lays approximately 35-40 bricks. For concrete blocks (CMU) with 1/2-inch joints, each bag covers 12-14 blocks. The calculator above takes your total wall area and joint size, then estimates the number of mortar bags, sand tonnage, and water volume needed. This eliminates guesswork and ensures you have enough material on-site before the masons arrive.

What Types of Mortar Are There?

Mortar is classified by type, each with a different strength and application. Type M is the strongest (2,500 psi minimum), used for below-grade foundations, retaining walls, and areas subject to severe weathering or soil pressure. Type S (1,800 psi) is the standard for exterior walls above grade and structural masonry. Type N (750 psi) is the general-purpose mortar for above-grade, non-structural work like veneer walls and interior partitions. Type O (350 psi) is the weakest, used for interior non-load-bearing walls and repointing historic brick where flexibility matters more than strength. Using the wrong type compromises either the wall strength or the brick durability.

What Is the Mortar Mix Ratio?

Site-mixed mortar uses Portland cement, hydrated lime, and sand. Type M: 1 part cement, 1/4 part lime, 3 parts sand. Type S: 1 part cement, 1/2 part lime, 4.5 parts sand. Type N: 1 part cement, 1 part lime, 6 parts sand. Pre-mixed mortar bags contain cement, lime, and additives already blended in the correct proportions. You only add water. Pre-mixed bags are more convenient and consistent than site-mixing, especially for smaller projects. For large commercial jobs, ordering pre-blended dry mortar by the ton from a masonry supplier is more cost-effective than buying individual 80-pound bags.

How Much Sand Do I Need for Mortar?

When using pure Portland cement and lime (not pre-mixed bags), sand is the largest component by volume. The sand-to-cement ratio ranges from 3:1 to 6:1 depending on mortar type. For a Type S mix, every bag of cement requires about 200 pounds of mason sand. As a rule of thumb, plan one ton of sand for every 7-8 bags of cement in a Type S mix. The sand must be clean, well-graded mason sand (not play sand, beach sand, or sharp concrete sand). Mason sand has rounded grains that create a workable, cohesive mortar. Incorrect sand produces mortar that is either too stiff or too soupy and does not bond properly.

How to Mix Mortar Correctly?

Add dry ingredients to the mixer first and blend for one minute. Slowly add water while the mixer runs, aiming for a consistency similar to thick peanut butter. Mortar should hold its shape when squeezed and slide cleanly off the trowel without dripping. Too much water weakens the mortar and stains the brick. Too little water makes the mortar crumbly and difficult to spread. Mix only enough mortar to use within 90 minutes (the working time before the cement begins to set). Do not add water to retemper mortar that has started to stiffen from hydration, as this weakens the final bond.

How Much Mortar Does One Bag Cover?

An 80-pound bag of pre-mixed mortar (Type S or N) lays approximately 35-40 standard modular bricks with 3/8-inch joints. The same bag covers about 12-14 standard 8x8x16 CMU blocks with 3/8-inch bed joints and face-shell mortar bedding. For a brick wall project, estimate 1 bag per 35 bricks. For a block wall, estimate 1 bag per 12 blocks. These figures assume standard joint thickness and reasonable waste. Wider joints (1/2 inch) consume roughly 30% more mortar per unit. Completely filling block cells with mortar (instead of face-shell bedding only) dramatically increases mortar consumption.

What Is the Difference Between Mortar and Grout?

Mortar bonds masonry units together in joints. It is thick, stiff, and troweled into thin layers. Grout is a fluid mixture of cement, sand, and water (sometimes with small aggregate) poured into the hollow cells of concrete blocks to fill them around rebar. Grout has a higher water content than mortar so it flows into cavities. The two products are not interchangeable. Using mortar to fill block cells results in incomplete filling and voids around rebar. Using grout in mortar joints produces a weak, runny joint that does not support the masonry units properly.

Mortar for Repointing Existing Masonry

Repointing (also called tuck-pointing) replaces deteriorated mortar joints in existing walls. The old mortar is raked out to a depth of at least 3/4 inch using a grinder or hand tool. New mortar is packed into the joints in two lifts, allowing the first lift to firm up before adding the second. For historic buildings (pre-1920), use Type O or Type K (lime-only) mortar. These softer mortars are critical because the old soft brick was designed to work with flexible lime mortar. Using modern Type S or Type M on historic brick causes the brick to crack and spall because the hard mortar forces stress into the softer brick rather than absorbing movement.

Frequently asked questions