Concrete Masonry Guide
Concrete Block Mortar
Learn how mortar is used with concrete blocks, how mortar joints affect block walls, common mortar mix types, how much mortar a project may require, and what to consider when building or repairing a concrete block wall.
Quick Answer
What mortar is used for concrete blocks?
Concrete block walls are commonly built using masonry mortar placed between the individual concrete masonry units (CMUs). The mortar bonds the blocks together, fills the joints, helps transfer loads between units, and creates a weather-resistant masonry surface when properly installed.
The appropriate mortar type depends on the wall design, exposure, structural requirements, local building requirements, and the specifications for the project. Common mortar designations include Type N, Type S, and Type M, each intended for different masonry applications.
If you are estimating a block wall, start by calculating the number of blocks required with the Concrete Block Calculator . Mortar quantity should then be estimated from the actual block size, joint dimensions, wall layout, openings, and the mortar product being used.
What Is Concrete Block Mortar?
Concrete block mortar is a cement-based masonry material used to join concrete blocks together. It is placed in the horizontal and vertical joints between blocks as the wall is constructed.
Mortar is different from concrete. Although both can contain cement, sand, and water, they are designed for different purposes. Mortar is formulated to bond masonry units and remain workable during installation, while concrete is generally designed for structural mass, slabs, footings, columns, and other applications.
A masonry mortar mix commonly contains cementitious material, fine aggregate such as sand, water, and sometimes lime or other manufacturer-specified components. The exact formulation depends on the mortar type and whether the product is supplied as a pre-blended mix or prepared from individual ingredients.
Mortar
Designed for masonry jointsUsed to bond concrete blocks and fill the joints between masonry units.
Concrete
Designed for structural massCommonly used for slabs, footings, foundations, columns, and other concrete construction.
Mortar Mix for Concrete Blocks
There is no single mortar mix that should be used for every concrete block wall. Mortar selection depends on the type of masonry, the required strength, environmental exposure, wall design, and applicable construction requirements.
Mortar is commonly identified by types such as Type N, Type S, and Type M. These types have different strength and performance characteristics and are intended for different masonry situations.
General-purpose mortar
A commonly used mortar for many above-grade masonry applications where moderate strength and good workability are appropriate.
Higher-strength mortar
Used in applications where greater compressive strength and stronger bond characteristics are required by the project.
High-strength mortar
A high-strength mortar type used for certain demanding masonry applications when specified by the design or applicable requirements.
A stronger mortar is not automatically the correct mortar for every wall. Masonry systems are designed so the mortar, block, joints, reinforcement, and surrounding construction work together. Follow the project specifications, applicable code, and manufacturer's instructions when selecting mortar.
Common Mortar Types for Concrete Block Walls
The three mortar types below are frequently discussed when selecting mortar for masonry construction. Their suitability depends on the specific wall and design requirements.
| Mortar type | General characteristic | Typical consideration |
|---|---|---|
| Type N | Moderate strength and good workability | Many general above-grade masonry applications |
| Type S | Higher strength than Type N | Applications requiring stronger masonry performance |
| Type M | Highest compressive strength of these common types | Selected heavy-duty or structural masonry applications |
Mortar specifications can vary by product and standard. If you are using bagged mortar, use the manufacturer's mixing instructions rather than trying to recreate the product formula from a generic recipe.
How Thick Should Mortar Be Between Concrete Blocks?
Mortar joints are normally much thinner than the concrete blocks themselves. A commonly used masonry planning dimension is approximately 3/8 inch for a mortar joint, although the required joint dimensions can vary with the construction system and project specifications.
Mortar joints occur both horizontally between courses and vertically between adjacent blocks. These joints are important because they affect the installed module of the wall.
Bed joint
The horizontal mortar joint placed between one course of concrete blocks and the course above it.
Head joint
The vertical mortar joint between the ends of adjacent concrete blocks.
Joint tooling
Finishing the exposed mortar joint can improve its appearance and can help produce the specified joint profile.
Why Mortar Joints Matter for Block Quantity
Mortar joints are one reason concrete block sizes are often described using nominal dimensions. For example, a common nominal block may be described as 8 × 8 × 16 inches even though its physical dimensions are slightly smaller.
The mortar joint fills part of the difference between individual block dimensions and the installed wall module. This makes it easier to plan courses and estimate masonry quantities.
For a typical nominal 8 × 8 × 16 inch block, the nominal face area is approximately 0.89 square feet. A basic planning estimate therefore works out to roughly 1.125 blocks per square foot before considering openings, corners, cuts, specialty units, or waste.
Use your actual block dimensions instead of assuming every concrete block is 8 × 8 × 16 inches. The Concrete Block Calculator lets you estimate the required number of blocks using your project dimensions.
How Much Mortar Do You Need for Concrete Blocks?
The amount of mortar required for a concrete block wall depends on several variables. There is no single bag-per-block figure that works for every project.
Block size
Larger blocks may require a different amount of mortar per unit because the joint layout and block geometry change.
Wall area
A larger wall naturally requires more mortar joints and therefore more total mortar.
Joint dimensions
Joint thickness and the amount of mortar placed in each joint affect the total material requirement.
Openings and layout
Doors, windows, corners, cuts, intersections, and specialty units can change the amount of mortar needed.
The most reliable way to estimate bag quantities is to calculate the masonry area and block layout first, then use the coverage information provided by the specific mortar manufacturer. Bag sizes and stated coverage can vary considerably between products.
How Many Concrete Blocks Per Bag of Mortar?
The number of concrete blocks that can be laid with one bag of mortar depends on the block dimensions, joint thickness, joint profile, workmanship, wall configuration, and the coverage rating of the particular mortar product.
Because of these variables, a universal number of blocks per bag is not a reliable estimating rule. Instead, check the product's published coverage and compare it with the actual block layout for your wall.
Better estimating method
Use manufacturer coverage instead of a generic bag count
If a mortar product states that one bag covers a particular number of square feet of standard masonry, divide your total masonry area by that coverage. Then account for openings, job conditions, and a reasonable allowance for waste.
How to Mix Mortar for Concrete Blocks
If you are using a pre-blended mortar product, follow the water quantity and mixing procedure printed on the bag or technical data sheet. Adding too much or too little water can change the consistency and performance of the mortar.
Read the product instructions
Check the mortar type, recommended water range, mixing time, and handling instructions before starting.
Measure the water
Start with the manufacturer's specified water amount rather than adding water by guesswork.
Mix thoroughly
Mix the material using the recommended equipment and procedure until the mortar reaches the specified consistency.
Check workability
The mortar should be workable enough to place and tool correctly without becoming excessively wet.
Pre-blended masonry mortar is formulated to a specified product standard and comes with manufacturer instructions. If you are preparing mortar from separate ingredients, the required proportions depend on the specified mortar type and applicable masonry standard. Do not substitute a generic concrete recipe for masonry mortar.
Mortar vs. Concrete for Concrete Blocks
One common mistake is assuming that mortar and concrete are interchangeable because both materials contain cementitious ingredients. They are not designed for the same job.
| Material | Primary purpose | Typical characteristics |
|---|---|---|
| Masonry mortar | Bonding masonry units | Workable material designed for masonry joints |
| Concrete | Structural mass and formed elements | Coarse aggregate is commonly used and the material is designed for different applications |
| Grout | Filling designated cores or reinforced spaces | Designed to flow into spaces where specified by the masonry system |
Mortar, concrete, and grout can all appear in the same masonry project, but they serve different functions. The construction drawings and project specifications determine where each material belongs.
Mortar for Concrete Block Wall Construction
Building a concrete block wall involves more than simply stacking blocks and applying mortar. The blocks need to be laid in the specified pattern, joints need to be properly formed, and the wall may require reinforcement, grout, anchors, control joints, or other components depending on its design.
Determine the wall length, height, openings, corners, and required block arrangement before estimating materials.
Verify the nominal and actual dimensions of the CMU being used. Different block widths and specialty units change the layout.
Use the mortar type specified for the project rather than choosing a mix solely because it has a higher strength rating.
Doors, windows, corners, reinforcement, lintels, and specialty units can affect both block and mortar requirements.
How to Mortar Concrete Blocks
The basic process of laying concrete blocks with mortar involves preparing the mortar, establishing the wall layout, applying mortar to the appropriate surfaces, positioning each block, and maintaining the specified joint dimensions and alignment.
The exact construction procedure depends on the type of wall and the masonry specifications. For a typical masonry installation, the following sequence illustrates the basic concept.
Prepare the base
Make sure the foundation or supporting surface is prepared according to the project requirements.
Establish the first course
The first course is especially important because its alignment affects the courses above it.
Apply mortar
Place mortar according to the specified joint arrangement and masonry practice.
Set the block
Position the block carefully while maintaining the required line, level, plumb, and joint dimensions.
Build successive courses
Continue the specified bond pattern while maintaining consistent joints and checking alignment as the wall rises.
Tool the joints
Finish exposed joints at the appropriate stage and according to the required joint profile.
How Much Mortar Goes Between Concrete Blocks?
Mortar is placed in the joints between blocks rather than throughout the entire interior volume of a hollow CMU. The quantity therefore depends heavily on the surface area and configuration of the joints.
A wall made from standard blocks may have many linear feet of horizontal and vertical joints. Corners, openings, cuts, pilasters, and specialty units can increase or change the amount of mortar required.
For this reason, estimating mortar by simply multiplying the number of blocks by one fixed mortar amount can produce inaccurate results. Manufacturer coverage data and the actual wall layout provide a better basis for material planning.
Concrete Block Mortar Repair
Over time, mortar joints in concrete block walls can crack, deteriorate, or lose material. Minor joint deterioration is often addressed through masonry repair techniques, while larger cracks or movement can indicate an underlying issue that needs further evaluation.
Surface deterioration
Small areas of weathered or deteriorated mortar may require removal of loose material followed by appropriate repointing.
Cracked joints
Cracking should be evaluated based on its size, pattern, location, and whether there is evidence of movement in the wall.
Recurring damage
If repaired mortar repeatedly cracks or separates, the underlying source of movement, moisture, settlement, or structural stress should be investigated.
Significant wall movement, large cracks, bulging masonry, foundation movement, or structural damage should be evaluated by a qualified professional rather than treated as a simple mortar repair.
Concrete Block Mortar Example
Suppose a project has a rectangular concrete block wall measuring 20 feet long by 8 feet high.
The wall area is:
If nominal 8 × 8 × 16 inch blocks are being used, a simplified planning estimate is approximately 1.125 blocks per square foot:
That number is only a basic block estimate. A real project may have doors, windows, corners, cuts, specialty units, and waste. The mortar requirement must then be estimated from the actual block layout and the coverage information for the selected mortar product.
If you want to estimate the block quantity for your own wall, use the Concrete Block Calculator and enter your wall dimensions and block size.
Factors That Affect Concrete Block Mortar Quantity
Two walls with the same total square footage can require different amounts of mortar. The following factors can change the final requirement:
Block dimensions
Block height and length affect the total number and length of masonry joints.
Joint thickness
Larger or smaller joints can change the amount of mortar placed between units.
Wall openings
Openings remove wall area but can also introduce additional corners and detail work.
Waste and job conditions
Material handling, spillage, cleanup, and site conditions can affect the amount actually consumed.
Concrete Block Mortar Tips
Check the mortar specification first. Use the mortar type and product specified for the project.
Verify block dimensions. Nominal sizes are useful for planning, but actual products can differ.
Follow the bag instructions. Do not guess the water-to-mix ratio when using a packaged mortar product.
Do not use concrete as a direct substitute for mortar. The two materials are designed for different purposes.
Plan for waste. Actual material consumption can be higher than a theoretical calculation.
Calculate Your Concrete Block Requirements
Nerdds Calculator
Know Your Wall Dimensions? Calculate the Blocks.
Enter your wall dimensions, block size, openings, and waste allowance to estimate the number of concrete blocks required for your project. Use the result as a planning estimate and verify materials against your construction plans and supplier specifications.
Open Concrete Block Calculator →Frequently Asked Questions
What mortar is used for concrete blocks?
Concrete block walls are commonly built using masonry mortar. Common mortar types include Type N, Type S, and Type M, but the correct type depends on the wall design, project specifications, exposure, and applicable requirements.
What is the best mortar mix for concrete blocks?
There is not one mortar mix that is correct for every concrete block project. Type N, Type S, and Type M have different properties and are used for different applications. Follow the project specification or the recommendation provided by the applicable masonry standard and product manufacturer.
How thick should mortar be between concrete blocks?
A commonly used masonry planning dimension is about 3/8 inch for mortar joints, but the required joint dimensions can vary depending on the masonry system and project specifications.
How many blocks can one bag of mortar lay?
The number varies with block size, joint dimensions, workmanship, wall configuration, and the mortar product. Check the manufacturer's coverage information rather than relying on a universal blocks-per-bag number.
How much mortar do I need for a concrete block wall?
Mortar quantity depends on the wall area, block dimensions, joint dimensions, openings, layout, and product coverage. Calculate the masonry area first and then use the coverage information for the specific mortar product.
Can I use concrete instead of mortar for concrete blocks?
Concrete should not simply be substituted for masonry mortar. Mortar is specifically designed to bond masonry units and form masonry joints, while concrete is designed for different construction applications.
What is the difference between mortar and grout?
Mortar is primarily used in the joints between masonry units. Grout is a different material designed to fill specified spaces such as reinforced CMU cores or other cavities. They are not automatically interchangeable.
How do I estimate mortar for a block wall?
Start with the wall dimensions and block layout, then determine the number and length of mortar joints. Compare the resulting requirement with the coverage information for the mortar product you plan to use, and include an allowance for waste and job conditions.
How many concrete blocks do I need for my wall?
The number depends on wall length, wall height, block dimensions, openings, and waste. Use the Concrete Block Calculator to estimate the number of blocks for your project.