How Repair Mortar Bags Are Calculated
Repair mortar is bought by the bag, and each bag fills a known volume. The calculation compares the cavity you cut with that yield.
1
Cavity Volume
Length × width × depth in inches, divided by 1,728. A 24 × 24 in patch 1-1/2 in deep is 864 cubic inches, or 0.5 cubic feet.
2
Divide by Yield
A 50 lb bag of Planitop 18 TG yields 0.41 cubic feet neat. Dividing 0.5 by 0.41 gives 1.22 bags before overage.
3
Add Overage
Multiply by 1 plus your overage. At 10%, 1.22 bags becomes 1.34 bags to cover scrubcoat, spill, and uneven cavity floors.
4
Round Up
You cannot buy part of a bag, so 1.34 rounds up to 2 bags. Water and lifts follow from the bag count and depth.
Repair Mortar Yields and Limits Side by Side
Each mortar has its own yield, lift range, and water. Use these Mapei data sheet figures to check the calculator or to compare products before you buy.
| Item |
Planitop 18 TG |
Planitop 18 |
Planitop 12 SR |
| Bag size | 50 lb | 50 lb | 55 lb |
| Yield, neat | 0.41 ft³ | 0.42 ft³ | 0.46 ft³ |
| Yield, extended | 0.58 ft³ (40 lb pea gravel) | 0.64 ft³ (80% extension) | Not extended |
| Depth per lift | 1/2 to 2 in neat; up to 8 in extended | 1/2 in minimum neat; 2 to 8 in extended | 1/4 to 2 in; overhead 1 in per lift |
| Orientation | Horizontal | See data sheet | Vertical, overhead, horizontal |
| Mixing water | Up to 2.8 qt per bag | 2.5 to 3 qt per bag | 0.82 to 0.99 gal per bag |
Source: MAPEI technical data sheets for each product. Yields are for estimating only. Actual coverage varies with climate and substrate.
Planitop 18 TG meets or exceeds ASTM C928 R3 requirements and can open to vehicle traffic in under 2 hours at 73°F, per its data sheet.
Bags for Common Patch Sizes
Find a patch near yours to sanity-check the calculator. Volumes are cubic feet, and bags are before overage.
| Patch Size (L × W × D) |
Volume |
Planitop 18 TG, Neat |
Planitop 12 SR |
| 12 × 12 × 1 in | 0.083 ft³ | 0.20 bags | 0.18 bags |
| 12 × 12 × 2 in | 0.167 ft³ | 0.41 bags | 0.36 bags |
| 24 × 24 × 1.5 in | 0.500 ft³ | 1.22 bags | 1.09 bags |
| 24 × 24 × 2 in | 0.667 ft³ | 1.63 bags | 1.45 bags |
| 36 × 36 × 2 in | 1.500 ft³ | 3.66 bags | 3.26 bags |
| 48 × 48 × 2 in | 2.667 ft³ | 6.50 bags | 5.80 bags |
Calculated as L × W × D ÷ 1,728, then divided by yield. The 12 SR column uses 55 lb bags.
For multiple repairs at different depths, run each depth separately. The concrete patch calculator works for general patching volume.
Repair Mortar Is Not Masonry Mortar
Search results for "mortar calculator" often show tools for brick and block walls. Those tools size Type N, S, M, or O mortar and work from unit counts and joint widths.
Concrete repair mortar is a different product. It is a packaged cementitious material, often shrinkage-compensated, used to rebuild damaged concrete. Mapei's Planitop 18 TG, for example, is classified under ASTM C928.
Repair starts with finding why the concrete failed. See concrete spalling and concrete delamination to identify the damage before you cut a patch.
Not every defect needs a deep patch. For shallow damage, try the guide on patching concrete without removing the old concrete, and use the concrete crack filler calculator for narrow cracks.
Rebar depth also matters. Check concrete cover requirements so the repair restores protective cover, and see how to use concrete bonding adhesive when a product calls for one. Mapei notes that Planibond 3C is not to be used with Planitop 18 TG.
Prep, Placement, and Cure
🧰
Surface Profile
The Planitop 18 TG data sheet calls for an ICRI 310.2R profile of CSP 5 or greater. ICRI 310.2R defines profiles CSP 1 through 10.
💧
Saturated Surface Dry
The substrate should be saturated surface dry with no standing water. Apply a scrubcoat of the repair mortar before placing the full depth.
🔩
Behind the Rebar
Leave at least 3/4 inch of clearance behind reinforcing steel so the mortar can surround the bar. Get repair geometry from ICRI 310.1R and ACI RAP Bulletin 7.
🌡️
Temperature and Curing
Keep ambient temperature between 45°F and 85°F while Planitop 18 TG cures, and protect it from freezing for 12 hours. See the concrete curing time chart for general guidance.
Larger repairs may need a full topping. Compare with the concrete resurfacing calculator and the concrete repair calculator.
To price the whole job with labor, use the concrete repair cost calculator.
Sample Repair Takeoffs
These sample calculations show how a contractor might size three different repairs. They are illustrations, not documented projects.
🏢 Garage Slab Spall
Product: Planitop 18 TG, neat
Patch: 24 × 24 in, 1-1/2 in deep
Overage: 10%, horizontal
Volume: 576 × 1.5 ÷ 1,728 = 0.500 ft³
Bags: 0.5 ÷ 0.41 = 1.22; with 10% = 1.34
Buy: 2 bags (50 lb)
Water: 2 × up to 2.8 qt = up to 5.6 qt
Depth is within the 1/2 to 2 in neat range, so this is one lift.
🅿️ Parking Deck Repairs, Extended
Product: Planitop 18, extended
Patches: 10 patches, 12 × 12 in, 3 in deep
Overage: 10%
Volume: 10 × 144 × 3 ÷ 1,728 = 2.500 ft³
Bags: 2.5 ÷ 0.64 = 3.91; with 10% = 4.30
Buy: 5 bags; pea gravel 5 × 40 = 200 lb
Planitop 18 extended is for 2 to 8 in depths, so 3 in fits in one lift.
🌉 Soffit Repair, Overhead
Product: Planitop 12 SR
Repair: 4 ft² at 2 in deep, overhead
Overage: 10%
Volume: 4 × 2 ÷ 12 = 0.667 ft³
Bags: 0.667 ÷ 0.46 = 1.45; with 10% = 1.59
Buy: 2 bags (55 lb)
Lifts: 2 lifts of 1 in each
The data sheet limits overhead placement to 1 in per lift, so the same repair takes two passes.
Sources and Method
- MAPEI mortar beds and concrete repair mortars calculator (5% to 10% overage guidance): mapei.com
- MAPEI Planitop 18 TG technical data sheet (yield 0.41 and 0.58 cu ft, lifts, water, CSP 5, rebar clearance, ASTM C928 R3): Planitop 18 TG TDS
- MAPEI Planitop 18 technical data sheet (yield 0.42 and 0.64 cu ft, water, depth limits): Planitop 18 TDS
- MAPEI Planitop 12 SR technical data sheet (yield 0.46 cu ft per 55 lb, lifts, overhead limit, water): Planitop 12 SR TDS
- ICRI Technical Guideline 310.2R-2013, Selecting and Specifying Concrete Surface Preparation (CSP 1 through 10): ICRI overview article
- ICRI technical publications, including 310.1R repair guidance: icri.org
- Masonry mortar contrast (Types N, S, M, O): mortarcalculator.com
Volume = L × W × D ÷ 1,728 per patch, times the number of patches. Bags = volume ÷ yield, plus overage, rounded up. Yields are Mapei estimating figures, and actual coverage varies with jobsite conditions.
Last reviewed: October 2026. Reviewed by site author.
⚠️ Disclaimer
This calculator provides estimates for planning purposes. For permitted structural work, foundations, multi-story construction, retaining walls over 4 feet, and commercial projects, calculations must be verified by a licensed structural engineer per IBC 2024 §1604. ConcreteCalculate.com is not liable for structural decisions made from these estimates.
ConcreteCalculate.com is not affiliated with MAPEI. Structural concrete repair, including repairs near reinforcing steel, should follow an engineer's repair design and the product manufacturer's current data sheet.
Calculations run entirely in your browser. No project data is stored or transmitted to any server beyond the calculation request itself.
