Mortar Calculator
Estimate how much mortar you need for your brick or block project. Enter the number of bricks, joint thickness, and mortar type to calculate volume and the number of 80lb bags required.
Understanding Mortar for Brick and Block Projects
Mortar is the binding material that holds bricks, blocks, and stone together in masonry construction. It fills the joints between units, providing structural bond, weather resistance, and a finished appearance. Choosing the right type and estimating the correct quantity of mortar is critical to the success of any masonry project.
A standard modular brick with 3/8-inch mortar joints requires approximately 0.025 cubic feet of mortar per brick. One 80-pound bag of pre-mixed mortar covers about 35 standard bricks. For larger projects, mortar can be mixed from individual components (Portland cement, lime, and sand) which is more economical but requires precise proportioning.
Types of Mortar
Mortar is classified by type according to ASTM C270. Each type has different proportions of Portland cement, hydrated lime, and sand, giving it distinct properties suited for specific applications:
- Type N (General Purpose): A medium-strength mortar with good bonding properties and workability. It is the most commonly used mortar type for general above-grade construction. Type N is recommended for exterior and interior load-bearing walls, chimneys above the roofline, and soft stone applications. Its compressive strength is approximately 750 PSI.
- Type S (Structural): A high-strength mortar with excellent bonding characteristics. Type S is used for structural applications, exterior walls at or below grade, retaining walls, sewers, manholes, and masonry exposed to high winds or seismic forces. Its compressive strength is approximately 1,800 PSI.
- Type M (Below Grade): The highest compressive strength mortar at approximately 2,500 PSI. Type M is used for below-grade applications like foundations, retaining walls, driveways, walks, and heavy load-bearing walls. Despite its strength, it has lower workability and bond strength compared to Type N and S.
- Type O (Non-Structural): A low-strength mortar used primarily for interior non-load-bearing walls, repointing, and restoring historic masonry. Its compressive strength is approximately 350 PSI. Type O should not be used in wet or freezing environments.
When to Use Each Mortar Type
Selecting the right mortar type ensures your project will be structurally sound and durable:
- Above-grade exterior walls: Type N or Type S
- Below-grade walls and foundations: Type S or Type M
- Retaining walls: Type S
- Chimneys: Type N above the roofline, Type S below
- Paving and walkways: Type M
- Interior non-load-bearing walls: Type N or Type O
- Historic restoration: Type O or a custom lime mortar matching the original
Mortar Mixing Tips
Proper mixing is essential for strong, workable mortar:
- Follow the manufacturer's water ratio: Add water gradually and mix thoroughly. Mortar should be stiff enough to hold its shape when troweled but plastic enough to spread easily.
- Mix only what you can use in 90 minutes: Mortar begins to set after about 90 minutes. Never add water to mortar that has started to harden (called re-tempering), as this weakens the final bond.
- Consistency matters: The mortar should cling to a vertical trowel surface. If it slides off immediately, it is too wet. If it crumbles, it needs more water.
- Temperature considerations: Do not mix or apply mortar when temperatures are below 40 degrees F or above 100 degrees F. Cold temperatures slow curing and can cause freeze damage, while extreme heat causes mortar to dry too quickly before it cures.
Frequently Asked Questions
How much mortar do I need per brick?
A standard modular brick (3-5/8" x 2-1/4" x 7-5/8") with a 3/8-inch mortar joint requires approximately 0.025 cubic feet of mortar. This accounts for mortar on both the bed joint (horizontal bottom) and head joint (vertical side) of each brick. An 80-pound bag of mortar mix yields enough mortar for approximately 35 standard bricks. Actual usage varies depending on joint thickness, brick size, and waste. It is wise to add 10 to 15 percent to your estimate for waste.
Which mortar type should I use?
The mortar type depends on your application. Type N is the most common all-purpose mortar for general above-grade construction like exterior walls and chimneys. Type S provides higher bond strength and is used for structural applications, below-grade walls, and areas subject to lateral forces like retaining walls. Type M has the highest compressive strength and is used for below-grade applications, foundations, and heavy load-bearing walls. When in doubt, Type N is a safe choice for most residential above-grade projects.
How many bricks can I lay with one bag of mortar?
One 80-pound bag of mortar mix will lay approximately 35 standard modular bricks with 3/8-inch joints. A 60-pound bag covers about 25 bricks. These estimates assume standard 3/8-inch bed and head joints with reasonable waste. Thicker joints or larger bricks will require more mortar per unit. For concrete blocks (CMU), one 80-pound bag covers approximately 12 standard 8x8x16 blocks. Always purchase 10 to 15 percent more than your calculated need to account for waste, spillage, and joint tooling.
Can I reuse mortar that has started to set?
No. Once mortar has begun its initial chemical set, adding water and remixing (re-tempering) significantly weakens the final strength and bond. Pre-mixed mortar has a working time of about 90 minutes after mixing. After that, it should be discarded. Plan your work to mix only the amount of mortar you can use within that time window. In hot or dry conditions, the working time may be shorter.