What Is Shotcrete vs. Gunite?
Shotcrete and gunite are both pneumatically placed concrete — sprayed at high velocity onto a surface — differing in when water is added: gunite (dry-mix) adds water at the nozzle; shotcrete (wet-mix, the modern dominant method) batches water at the plant and pumps the wet mix to the nozzle where air propels it. Both achieve excellent compaction and bond through the impact velocity. The terms are often used interchangeably; engineers usually mean wet-mix shotcrete.
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Dry-mix (gunite) vs. wet-mix (shotcrete)
Dry-mix: dry materials convey through the hose; the nozzleman adds water at the nozzle — instant start/stop, good for small or intermittent work, but water content depends on the nozzleman's skill (quality varies). Wet-mix: fully batched concrete pumps through the hose; air at the nozzle propels it — consistent water-cement ratio, higher production rates, better for large volumes. Modern specifications (ACI 506R) favor wet-mix for structural work; dry-mix persists for repairs and small placements.
Where it is used
Swimming pools (the classic application), tunnel linings and slope stabilization (with soil nails), retaining walls and seawalls, structural repairs (encasing deteriorated elements), and architectural freeform shapes. Anywhere forms are impractical or the surface is irregular — the spray conforms to the substrate and compacts on impact.
Quality and inspection
Nozzleman certification (ACI C660) matters more than in any other concrete work — the operator controls compaction, water content (dry-mix), and rebound. Test panels shot alongside the work get cored for strength verification. Rebound (material bouncing off — 10-25% in dry-mix) must not be worked back in. Reinforcement needs adequate clearance for the spray to encapsulate (congested bars cause shadowing voids behind them).
The bottom line
Shotcrete (wet-mix) and gunite (dry-mix) are sprayed concrete — for pools, tunnels, slopes, and repairs. Specify ACI 506, require certified nozzlemen, and test with shot panels.
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