Cinder Block Mortar Calculator | Free Construction Calculators

Calculate the precise amount of mortar needed for your cinder block or CMU masonry project with our professional mortar calculator. Determine exact quantities of Type S, Type N, or Type M mortar required for laying concrete masonry units in bags, cubic feet, and cubic yards. Our calculator accounts for different block sizes (8x8x16, 6x8x16, 12x8x16), mortar joint thickness (3/8-inch or 1/2-inch), and bedding methods (face shell or full bedding) to provide accurate material estimates for foundation walls, retaining walls, building structures, and block masonry projects. Perfect for contractors, masons, builders, and DIY enthusiasts planning material orders for residential foundations, commercial construction, garden walls, and structural masonry work. Get instant results showing bags needed, coverage rates, and mixing instructions.

Accurate Mortar Quantities

Calculate exact bags and volume needed based on block size and joint thickness

Multiple Mortar Types

Coverage rates and mixing ratios for Type S, Type N, and Type M mortar

Bedding Method Options

Calculations for face shell bedding and full bedding applications

How to Use This Calculator

  1. Enter the total number of blocks you will be laying for your project
  2. Select your block size (standard 8x8x16 is most common for general construction)
  3. Choose mortar joint thickness (3/8-inch standard, 1/2-inch for thicker joints)
  4. Click Calculate to see bags needed, cubic feet, and coverage information
  5. Add 5-10% extra for waste, spillage, and inconsistent joint thickness
  6. Select appropriate mortar type (Type S for most CMU work, Type N for non-load bearing, Type M for below-grade)

Calculation Formula

Face shell bedding: Approximately 2.5 cubic feet of mortar per 100 standard blocks (3/8-inch joints)

Full bedding: Approximately 3.75 cubic feet of mortar per 100 standard blocks (50% more than face shell)

Bags needed: Total cubic feet ÷ 0.56 (cubic feet per 80-lb bag)

Coverage per bag: One 80-lb bag covers 12-15 standard blocks with face shell bedding

About Cinder Block Mortar Calculations

Accurate mortar quantity calculations are essential for concrete masonry projects to ensure adequate material supply, prevent construction delays, and control costs through precise ordering. Mortar requirements vary significantly based on block size, joint thickness, bedding method, and mason technique. Standard 8x8x16 concrete masonry units laid with face shell bedding (mortar applied only to outer shells, not center web) using 3/8-inch joints require approximately 2.5 cubic feet of mortar per 100 blocks. This translates to one 80-pound bag of pre-mixed mortar covering 12-15 blocks, or approximately 7-8 bags per 100 blocks. Full bedding mortar application, where mortar covers the entire horizontal block surface including webs, increases consumption by 50-60% to approximately 3.75 cubic feet per 100 blocks or 11-12 bags per 100 blocks. Face shell bedding is standard practice for most CMU construction and adequate for load-bearing walls when properly designed with appropriate reinforcement.

Mortar type selection significantly impacts wall performance, durability, and structural capacity. Type S mortar (1 part portland cement, 1/2 part hydrated lime, 4.5 parts sand by volume) is the most common choice for concrete masonry unit construction, providing 1,800 PSI compressive strength ideal for general purpose above-grade and below-grade load-bearing walls. Type S offers excellent bond strength, workability, and resistance to freeze-thaw cycles. Type N mortar (1 part cement, 1 part lime, 6 parts sand) provides 750 PSI strength suitable for above-grade non-load bearing walls, interior partitions, and veneer applications where lower strength is acceptable and improved workability is beneficial. Type M mortar (1 part cement, 1/4 part lime, 3 parts sand) delivers 2,500 PSI compressive strength for below-grade applications, retaining walls, foundations, heavy load-bearing walls, and severe frost exposure conditions, though reduced lime content makes it less workable and more prone to shrinkage cracking.

Proper mortar mixing, consistency, and application technique directly affect wall strength, water resistance, and long-term durability. Pre-mixed bagged mortar (80-pound bags at $10-$15 each) offers convenience, consistent quality, and reduced mixing labor ideal for small to medium projects under 500 blocks. For large commercial projects exceeding 1,000 blocks, field-mixed mortar using bulk portland cement ($10-$15 per 94-lb bag), hydrated lime ($12-$18 per 50-lb bag), and masonry sand ($25-$50 per cubic yard) reduces material costs 30-50% but requires on-site batching equipment, quality control, and experienced mixing labor. Proper mortar consistency should resemble thick peanut butter, spreading smoothly yet retaining shape without slumping. Mix only quantities usable within 2-2.5 hours (90-150 minutes in hot weather, up to 3 hours in cool conditions). Never retemper mortar by adding water after initial set begins - this dramatically reduces bond strength and durability. Maintain consistent joint thickness throughout the project: 3/8-inch joints are standard for CMU, with 1/2-inch joints acceptable but requiring 30-35% more mortar.

Mortar Types for Cinder Block Construction

Type S Mortar (Most Common for CMU)

  • Strength: 1,800 PSI compressive strength, medium-high performance
  • Mix Ratio: 1 part portland cement : 1/2 part hydrated lime : 4.5 parts masonry sand
  • Applications: General purpose load-bearing walls, above and below-grade, structural CMU
  • Characteristics: Excellent bond, good workability, freeze-thaw resistant, most versatile
  • Cost: $10-$15 per 80-lb pre-mixed bag, moderate cost for field mixing

Type N Mortar (Medium Strength)

  • Strength: 750 PSI compressive strength, general purpose
  • Mix Ratio: 1 part portland cement : 1 part hydrated lime : 6 parts masonry sand
  • Applications: Above-grade non-load bearing walls, interior partitions, veneers, chimneys
  • Characteristics: Superior workability, high lime content, flexible, less cracking
  • Cost: $9-$13 per 80-lb bag, most economical for field mixing

Type M Mortar (High Strength)

  • Strength: 2,500 PSI compressive strength, maximum strength
  • Mix Ratio: 1 part portland cement : 1/4 part hydrated lime : 3 parts masonry sand
  • Applications: Below-grade foundations, retaining walls, heavy loads, severe frost exposure
  • Characteristics: Very high strength, reduced workability, higher shrinkage, less flexible
  • Cost: $11-$16 per 80-lb bag, higher cement content increases cost

Mortar Bedding Methods

Face Shell Bedding (Standard)

  • Coverage: 2.5 cubic feet per 100 blocks (3/8-inch joints)
  • Bags needed: 7-8 bags per 100 standard 8x8x16 blocks
  • Application: Mortar applied only to outer face shells (approximately 1-1.25 inches wide each side)
  • Advantages: Uses 40% less mortar, faster application, adequate for most CMU construction
  • Uses: Standard for load-bearing walls, foundations, structural CMU with proper reinforcement
  • Code acceptance: Meets building codes when designed with appropriate reinforcement

Full Bedding (Complete Coverage)

  • Coverage: 3.75 cubic feet per 100 blocks (50% more than face shell)
  • Bags needed: 11-12 bags per 100 standard 8x8x16 blocks
  • Application: Mortar covers entire horizontal surface including face shells and center webs
  • Advantages: Maximum bond area, better sound transmission reduction, superior weather resistance
  • Uses: First course on footings, below-grade walls, fire walls, maximum strength requirements
  • Requirements: Often specified for below-grade, severe exposure, or acoustical applications

Mortar Coverage Rates by Block Size

  • Standard 8x8x16 blocks: 12-15 blocks per 80-lb bag (face shell), 8-10 blocks per bag (full bedding)
  • Half 8x8x8 blocks: 18-22 blocks per 80-lb bag (face shell), 12-15 blocks per bag (full bedding)
  • Narrow 6x8x16 blocks: 15-18 blocks per 80-lb bag (face shell), 10-13 blocks per bag (full bedding)
  • Wide 12x8x16 blocks: 8-10 blocks per 80-lb bag (face shell), 5-7 blocks per bag (full bedding)
  • Per 100 sq ft wall: 9-10 bags for standard 8x8x16 blocks with face shell bedding (112.5 blocks)

Frequently Asked Questions

How many bags of mortar do I need for 100 cinder blocks?

For 100 standard 8x8x16 cinder blocks laid with face shell bedding and 3/8-inch joints, you need approximately 7-8 bags of 80-pound pre-mixed mortar. This assumes typical mason technique applying mortar to outer face shells only (standard practice for CMU). If using full bedding where mortar covers the entire block surface including center webs, you need 11-12 bags per 100 blocks (50% more mortar). Always add 5-10% extra for waste, spillage, dropped mortar, and variation in joint thickness. For a 100-block project, order 8-9 bags for face shell bedding or 12-13 bags for full bedding. Experienced masons may achieve slightly better coverage (up to 15 blocks per bag), while less experienced workers or thick joints may require more mortar (10-12 blocks per bag). Weather conditions, block surface texture, and mortar consistency also affect coverage rates.

Should I use Type S or Type N mortar for cinder block walls?

Use Type S mortar for most cinder block applications including load-bearing walls, structural CMU, foundations, both above-grade and below-grade construction, retaining walls, and any application requiring 1,800 PSI strength and excellent bond. Type S is the standard choice for concrete masonry unit construction, offering optimal balance of strength (1,800 PSI), workability, bond performance, and freeze-thaw durability. Use Type N mortar only for non-structural applications including above-grade interior partitions, non-load bearing walls, decorative veneer over wood or steel framing, chimneys, and lightweight applications where 750 PSI strength is adequate. Type N offers superior workability due to higher lime content but lacks strength for structural use. For below-grade foundations, severe frost exposure, or maximum strength requirements, consider Type M mortar providing 2,500 PSI strength, though reduced workability and increased shrinkage make it less ideal for general CMU work. When in doubt, specify Type S - it handles 95% of concrete masonry applications effectively.

What is the difference between face shell and full bedding mortar?

Face shell bedding applies mortar only to the outer face shells (approximately 1-1.25 inches wide on each side) of hollow concrete blocks, leaving center webs unmortared. This is standard practice for CMU construction, using 40% less mortar while providing adequate bond strength when walls are properly designed with vertical and horizontal reinforcement. Face shell bedding requires 2.5 cubic feet of mortar per 100 blocks or 7-8 bags, allows faster wall construction, reduces material costs, and meets building codes for both load-bearing and non-load bearing applications. Full bedding applies mortar across the entire horizontal block surface including face shells and center webs, providing maximum bonded area but requiring 50% more mortar (3.75 cubic feet per 100 blocks or 11-12 bags). Full bedding is typically specified for the first course resting on foundation footings, below-grade walls requiring maximum water resistance, fire-rated walls needing superior fire protection, sound-rated walls for acoustical performance, and applications specifically requiring maximum bond area. Unless plans specify full bedding, use face shell bedding for economic and efficient CMU construction.

How do I mix mortar for cinder block construction?

For pre-mixed 80-pound bags (recommended for projects under 500 blocks), empty bag into mortar mixer or wheelbarrow, add approximately 5-6 quarts of clean water per bag, mix thoroughly for 3-5 minutes until achieving thick peanut butter consistency that spreads smoothly but holds shape. Adjust water gradually - too wet causes slumping and weak joints, too dry prevents proper bonding. For field mixing (economical for large projects), combine 1 part portland cement, 1/2 part hydrated lime, and 4.5 parts damp masonry sand by volume for Type S mortar. Measure materials accurately using buckets or volume boxes for consistency. Mix dry ingredients thoroughly before adding water. Add water slowly while mixing until achieving proper consistency - mortar should spread smoothly, retain trowel ridges, and not slump or slide off blocks. Mix only quantities usable within 2-2.5 hours maximum (90 minutes in hot weather over 90°F, up to 3 hours in cool weather). Never retemper mortar by adding water after initial set - this drastically reduces strength. Discard any mortar that has begun to stiffen. Clean tools and equipment immediately after use.

Can I reduce mortar costs for large cinder block projects?

Reduce mortar costs on large projects (over 1,000 blocks) by field-mixing mortar from bulk ingredients rather than buying pre-mixed bags, saving 30-50% on material costs. Purchase portland cement in 94-lb bags ($10-$15 each), hydrated lime in 50-lb bags ($12-$18), and masonry sand by the cubic yard ($25-$50 delivered) or ton. One 94-lb bag of portland cement, one 50-lb bag of lime, and approximately 0.5 cubic yards of sand produces equivalent of 12-15 bags of Type S mortar at roughly half the cost. Requires on-site mortar mixer ($50-$100 daily rental or $300-$600 purchase), proper batching containers for accurate proportioning, and experienced workers for quality control. For smaller projects under 500 blocks, pre-mixed bags offer better value when factoring equipment, labor, and convenience. Additional cost reduction strategies include using face shell bedding instead of full bedding (saves 40% mortar), maintaining consistent 3/8-inch joints (thicker joints waste mortar), training masons in efficient mortar application technique, protecting mixed mortar from sun and wind to maximize working time, and minimizing dropped or wasted mortar through proper site organization.

Related Cinder Block Calculators

→ Cinder Block Quantity Calculator - Calculate exact number of blocks needed→ Cinder Block Cost Calculator - Estimate complete project costs→ Cinder Block Wall Calculator - Calculate blocks for walls with openings

Professional Mortar Mixing and Application Tips

  • Maintain proper consistency: Mortar should spread smoothly yet retain trowel ridges without slumping
  • Add water gradually: Start with less water than you think needed - easier to add than remove
  • Mix thoroughly: No dry pockets or lumps - mix 3-5 minutes minimum for uniform consistency
  • Use within time limit: 2-2.5 hours maximum, less in hot weather - never retemper with water
  • Maintain consistent joints: 3/8-inch standard for CMU - use guide lines and consistent technique
  • Work in suitable temperatures: 40-90 degrees F ideal - protect from freezing and excessive heat
  • Keep materials clean: Use potable water, clean sand, and uncontaminated mixing equipment
  • Apply proper coverage: Face shell bedding standard - full bedding only when specified
  • Tool joints properly: Tool joints when thumbprint hard for proper compaction and water resistance
  • Order 10% extra: Account for waste, spillage, and variation in coverage rates