Calculate shotcrete volume for pools, tunnels, and retaining walls. Enter area and thickness with rebound waste factor for yards needed.
Shotcrete (also called gunite when applied dry) is concrete pneumatically sprayed at high velocity onto a surface. It's widely used for swimming pools, retaining walls, tunnels, slope stabilization, and repair work where formwork is impractical.
This calculator estimates the total shotcrete volume needed, including a rebound waste factor. Rebound is the material that bounces off the surface during application — typically 10–30% depending on the application angle, surface type, and nozzle technique.
Unlike poured concrete, shotcrete builds up thickness gradually and bonds directly to the receiving surface (rock, soil, or existing concrete). Accurate volume estimation with rebound factor prevents costly delays when ordering ready-mix concrete for shotcrete operations.
Tracking this metric throughout the project lifecycle helps project managers identify potential issues early and maintain quality standards from foundation to final inspection. Integrating this calculation into the estimating workflow reduces reliance on rules of thumb and improves the accuracy of material takeoffs and budget projections for every job.
Shotcrete applications have higher waste than poured concrete due to rebound. Failing to account for rebound waste means running out of material during a continuous spray operation, which can cause cold joints and weaken the structure. Accurate figures enable contractors to prepare competitive bids with confidence, reducing the risk of underestimating costs or overcommitting on project timelines and deliverables.
Design volume = Area (ft²) × Thickness (in) ÷ 12 ÷ 27 Rebound waste = Design volume × Rebound % (10–30%) Total volume = Design volume + Rebound waste Total yd³ = Area × Thickness / 12 / 27 × (1 + Rebound%)
Result: 26.7 yd³
Design: 1,200 ft² × 6"/12 ÷ 27 = 22.2 yd³. With 20% rebound: 22.2 × 1.20 = 26.7 yd³ total. The extra 4.5 yd³ accounts for material that bounces off during spraying.
Swimming pools and spas: the most common residential use. Retaining walls and slope stabilization: conforms to irregular surfaces. Tunnel linings: no formwork needed. Structural repairs: bonds to existing concrete. Water tanks and channels: seamless waterproof structures.
Wet-mix is pre-batched at a concrete plant and pumped through a hose. Dry-mix (gunite) mixes at the nozzle. Wet-mix produces less rebound and more consistent quality. Dry-mix allows longer hose distances and can be stopped and started easily.
Core samples should be taken from the finished shotcrete to verify strength and proper consolidation. Look for laminations (layers that didn't bond), sand pockets, and voids behind reinforcement. ACI 506 provides shotcrete quality standards.
Both are pneumatically applied concrete. Shotcrete (wet-mix) is pre-mixed concrete pumped through a hose. Gunite (dry-mix) sends dry material that's hydrated at the nozzle. Wet-mix has less rebound waste and more consistent quality.
Pool shells typically use 6–9 inches of shotcrete reinforced with #3 or #4 rebar on 12" centers. Floor thickness is usually 6" minimum, walls 6–8". Local codes may require specific minimums.
Rebound is concrete that bounces off the surface during spraying. It's not usable and must be removed. Rebound ranges from 10% on floor surfaces to 30% on overhead surfaces. Experienced nozzlemen reduce rebound through technique.
Shotcrete typically achieves 4,000–6,000 PSI compressive strength, comparable to or exceeding standard poured concrete. In-place quality depends heavily on nozzle technique and proper consolidation at the surface.
When properly applied, shotcrete achieves equal or slightly higher strength than poured concrete of the same mix design. The high-velocity impact provides good consolidation. However, poor nozzle technique can create voids and weak spots.
Typical shotcrete production rates are 5–25 yd³ per hour depending on equipment, crew size, and application conditions. A swimming pool (20–40 yd³) is typically shot in one day.