Example Data Table
| Scenario | Inputs | Outputs |
|---|---|---|
| Typical garage lift |
20 ft × 20 ft slab, 1.5 in lift, 70% coverage, 10% waste, 4 ft hole spacing, foam yield 2.5 ft³/unit |
Required volume ≈ 77.0 ft³ (2.85 yd³), Units ≈ 30.8, holes ≈ 36 (estimate) |
| Partial corner settlement |
22 ft × 18 ft slab, 2.0 in lift, 35% coverage, 12% waste, 4 ft spacing |
Lower volume and fewer holes due to reduced coverage |
Formula Used
How to Use This Calculator
- Measure the slab length and width, then choose unit system.
- Use Average Lift for uniform settlement, or Min/Max for uneven lift.
- Set Coverage (%) to the portion of the slab you will inject.
- Leave Void Fill at 100% unless only partial voids exist.
- Choose a yield per unit that matches your material specification.
- Enter your pricing, labor, overhead, and contingency for totals.
- Press Calculate to view results above the form.
- Use CSV or PDF buttons to export your estimate.
Settlement Patterns and Lift Planning
Garage slabs often settle near doors, corners, or utility trenches. Measure several elevations and note a practical lift range. If one corner is 2 inches low but most areas are 1 inch low, a midpoint lift better matches injection behavior. Keep joints free so the slab can move without binding.
Volume Estimation and Material Allowances
The estimator converts slab area and lift height into filled volume. For quick checks, multiply area by lift in feet. A 400 ft² slab lifted 1.5 inches is about 50 ft³ before factors. Coverage limits the repair zone, while void fill reflects whether you are lifting only or filling deep loss-of-support. Add waste for purge, leakage, and overfill. Many crews use 5% to 15%. Void fill below 100% can model spot injections where the slab bridges over shallow voids. When in doubt, keep void fill high and reduce coverage to match observed hollow zones. Record material used per hole.
Injection Hole Density and Spacing
Hole spacing drives lift control and drilling time. Closer spacing improves uniformity but increases labor. Many projects start around 3 to 5 feet and adjust for slab thickness, reinforcement, and lift sensitivity. The calculator estimates a grid count and scales it by coverage to support layout planning.
Cost Breakdown for Bids and Change Orders
Material can be priced per cubic foot or per unit yield, matching supplier quotes. Labor should include layout, drilling, injection, patching, and cleanup. Mobilization and equipment capture truck, generator, and pump setup. Overhead and contingency protect margins when field voids exceed expectations or access restrictions slow production.
Interpreting Results for Field Execution
Use required volume as a procurement target, not a guarantee. Foam yield varies with formulation and temperature, so verify published expansion and keep hose lengths reasonable. Grout yields are steadier but add dead load. Monitor lift response, slab cracking, and door clearances. Stop when grade is restored, then patch holes and document final elevations for future estimating.
FAQs
1) What lift height should I enter?
Use the average measured lift across the repair zone. If settlement is uneven, enter min and max lifts and let the estimator use their midpoint for volume.
2) How do I choose coverage percent?
Estimate the portion of the slab that will be injected. For example, a settled door edge might be 40% of the slab. Lower coverage reduces volume and hole counts.
3) When should void fill be less than 100%?
Use lower void fill when you expect limited voids and mostly need elevation correction. If the slab sounds hollow or shows pumping, keep void fill high to avoid under-ordering.
4) What is a reasonable waste factor?
Many crews use 5% to 15% depending on access, hose length, and purge losses. Increase waste for complex layouts, long lines, or when lift control requires extra injection.
5) Why are hole counts only an estimate?
Real hole layouts depend on reinforcement, cracking, utilities, and where the slab responds to injection. Use the grid estimate for planning, then adjust spacing on site.
6) Does this replace an engineer’s evaluation?
No. This is an estimating tool for quantities and costs. If the slab supports structural loads, shows major cracking, or has active soil issues, consult a qualified professional before repair.