Wet-Mix Shotcrete Placement and Nozzle Operation
Core concepts
The nozzleman controls three variables that decide whether wet-mix shotcrete bonds and consolidates: distance, angle, and motion. Hold the nozzle perpendicular (90°) to the receiving surface and roughly 0.9–1.5 m (3–5 ft) away. Closer than about 0.9 m concentrates impact and can gouge or rebound the material; farther than about 1.5 m loses velocity, so the stream fans out and bond and density fall off.
Move the nozzle in steady, overlapping circles or ovals so each pass covers fresh material before it stiffens. Do not hold the nozzle in one spot - that builds a lump, causes sagging, and starves the surrounding area. Build in lifts: overhead and vertical work in thinner lifts than floor work, letting each lift stiffen enough to support the next. Corners and shadowed areas (behind rebar, in pockets) must be filled first and squared off so the stream never has to shoot past an obstruction.
Traps in questions
- "Perpendicular" means to the surface being shot, not to the ground - on a wall it is horizontal, on a slope it tilts.
- A question describing a dry, dusty, rebounding stream usually points to too much distance or too steep an angle, not to a mix problem.
- Confusing rebound (material bouncing off) with overspray (material missing the target).
- Thinking faster nozzle travel improves production; erratic travel causes uneven thickness and cold joints.
Rule of thumb
If you can see individual particles ricocheting off the surface in quantity, you are too far away or off-angle - close in and square up before adjusting anything else.
Worked example
A nozzleman shooting a vertical wall notices heavy rebound and a porous-looking surface. He is standing about 2.5 m back and angled upward at roughly 60°. Correction: move to ~1.2 m and hold 90° to the wall; rebound drops and consolidation improves without touching the mix.