Why Use the Mortar Calculator?
Accurately calculating mortar volume is critical for masonry project management. Ordering too few bags halts construction mid-build, while over-ordering leads to spoiled cement bags hardening from moisture exposure. This Mortar Calculator streamlines estimation for both brickwork and concrete masonry unit (CMU) construction by factoring in unit coverage, bag yields (70lb vs 80lb), and jobsite waste allowances.
Key Benefits
- Multi-Unit Versatility: Supports standard modular face brick, 8” CMU block, and heavy 12” structural CMU block walls.
- Bag Yield Precision: Adjusts calculations for both 80 lb (~0.67 cu ft yield) and 70 lb (~0.58 cu ft yield) pre-mixed bags.
- Waste Management: Prevents material shortfalls by incorporating a customizable 10% to 20% waste margin for joint strike-offs and board droppings.
- Cost Control: Instantly converts unit requirements into total project material budgets.
Mortar Calculation Formulas
Mortar calculations rely on unit coverage factors combined with wet mix volume yields.
1. Brick Wall Mortar Requirement
Standard modular bricks require approximately $0.055$ bags of 80 lb mortar per square foot of wall area (or ~7 bags per 1,000 bricks with 3/8” bed joints):
\[N_{\text{brick\_bags}} = A_{\text{wall}} \times 0.055 \times \left(1 + \frac{W}{100}\right)\]Where: * $A_{\text{wall}}$ = Net wall surface area ($\text{ft}^2$) * $W$ = Waste percentage (%)
2. CMU Block Wall Mortar Requirement
For 8-inch concrete masonry units (112 blocks per $100\text{ ft}^2$), mortar usage is calculated as:
\[N_{\text{cmu8\_bags}} = A_{\text{wall}} \times 0.0336 \times \left(1 + \frac{W}{100}\right)\]For 12-inch concrete block, usage increases to $0.0470$ bags per square foot.
3. Bag Weight & Cubic Feet Conversion
When using 70 lb bags instead of standard 80 lb bags, a scaling factor of $\frac{80}{70} \approx 1.143$ is applied. Total mortar volume in cubic feet ($V_{\text{cuft}}$) is:
\[V_{\text{cuft}} = N_{\text{net\_80lb\_bags}} \times 0.67\]Real-World Masonry Mortar Comparison Table
The following reference table outlines typical material usage per 100 square feet of finished wall area across common masonry types (assuming standard 3/8” mortar joints and 80 lb bags):
| Masonry Unit Type | Units per 100 Sq Ft | Net 80lb Bags Needed | Net Cubic Feet | Estimated Material Cost ($12.50/bag) |
|---|---|---|---|---|
| Modular Face Brick | 700 Bricks | 5.5 Bags | 3.69 cu ft | $68.75 |
| 8” CMU Concrete Block | 112 Blocks | 3.4 Bags | 2.28 cu ft | $42.50 |
| 12” CMU Structural Block | 112 Blocks | 4.7 Bags | 3.15 cu ft | $58.75 |
| Manufactured Stone Veneer | 100 Sq Ft | 6.0 Bags | 4.02 cu ft | $75.00 |
Step-by-Step Guide: How to Estimate Mortar Requirements
- Calculate Net Wall Area: Multiply total wall length by wall height. Subtract window and door openings ($A_{\text{net}} = L \times H - A_{\text{openings}}$).
- Determine Masonry Unit: Identify whether you are laying standard face brick (700 units per $100\text{ ft}^2$) or CMU concrete blocks (112 units per $100\text{ ft}^2$).
- Select Mortar Bag Size: Verify bag weight on your material supply list. Standard pre-blended commercial bags come in 80 lb or 70 lb options.
- Apply Waste Allowance: Include a 10% waste factor for standard flat walls, or 15% for intricate walls with numerous piers, corners, or decorative soldier courses.
- Compute Total Order: Multiply total bag count by supplier unit cost to calculate your total masonry mortar budget.
Frequently Asked Questions (FAQ)
How many 80lb bags of mortar do I need for 100 sq ft of brick wall?
A standard 100 sq ft modular brick wall (requiring ~700 bricks) uses approximately 5.5 to 6 bags of 80 lb mortar mix, or about 6 to 7 bags when including a standard 10% waste factor.
How many 80lb mortar bags are needed per 100 CMU concrete blocks?
For standard 8”x8”x16” CMU concrete blocks, you need approximately 3 bags of 80 lb mortar mix per 100 blocks. For 12” CMU blocks, plan for approximately 4.2 bags per 100 blocks.
What is the yield in cubic feet for an 80lb mortar bag?
One 80 lb bag of pre-mixed masonry mortar yields approximately 0.67 cubic feet of wet, workable mortar when properly mixed with water.
What is the difference between Type N and Type S mortar?
Type N mortar has moderate compressive strength (~750 PSI) and is ideal for exterior non-loadbearing walls and interior brick veneer. Type S mortar has higher strength (~1,800 PSI) and is specified for below-grade foundations, structural CMU walls, and retaining walls.
Should I add sand to pre-mixed packaged mortar bags?
No. Pre-blended commercial mortar bags (like Quikrete or Sakrete Mortar Mix) already contain sand and cementitious materials in precise ratios. You only need to add clean water.
Why is a waste factor necessary when calculating mortar?
Mortar is subject to loss from board droppings, joint strike-off cleanup, uneven masonry unit dimensions, and stiffening (pot life expiration) during hot or windy weather.
Can I use this mortar calculator for stone veneer?
Yes, standard manufactured stone veneer typically uses mortar quantities similar to 8-inch CMU block walls due to heavy scratch coat scratch backing and thick bed joints.