Robotic or Hand Spraying: Choosing the Method

Shotcrete is concrete pumped through a delivery line and projected onto a surface at velocity, so it compacts as it lands. The nozzle can be held by a person or carried on the boom of a spraying rig. The concrete is the same. What changes is who controls what, how much air is at the nozzle, how far the nozzle sits from the surface and how thick each pass can go on.

Robotic Spraying

A robotic rig carries the nozzle on a boom. The operator stands at a control box or on a remote, in front of the machine, under supported ground and outside the sweep of the boom. On a rig the nozzleman controls the boom, the concrete pump, the accelerator dosing, the nozzle and the whole application from one place.

The operator keeps the nozzle at a constant distance and angle for the whole load. The target is 1 to 2 m from the substrate at 90 degrees. Air at the nozzle is 10 to 12 m³/min at 6 to 7 bar. Commonly used pass thicknesses are 50 to 100 mm overhead and 100 mm on a wall, with the trial setting what the mix will hold.

Tunnel primary linings, mine development headings and any large face with room for the machine are sprayed robotically. The operator stays back under supported ground while the nozzle works forward.

Hand Spraying

Hand spraying puts a person on the end of the delivery line. The nozzleman holds the nozzle, controls the air and accelerator taps at the nozzle end, and determines where the material goes and how thick it is. The pump operator runs the pump, watches the gauge, keeps the hopper at the right level and manages the line. Every change the nozzleman cannot make at the nozzle goes to the pump operator by hand signal.

The figures are different from the rig's. Nozzle distance is 1.0 to 1.5 m, because the smaller orifice and lower air volume lose velocity over a shorter distance. Air is 5 to 6 m³/min at the same 6 to 7 bar. Passes are 50 to 80 mm in any orientation, because an arm varies and a thick hand-placed pass fails at its thin spots.

Hand spraying suits small volumes, tight or irregular spaces, repair and patching, work over and around steel, and basement and civil faces. A nozzleman can change the angle instantly to work material in behind a bar. A boom has to be driven into position.

Choosing Between Them

• Access. A rig needs room to set up, place its stabilisers and deploy the boom. Detailed cross passages, portal connections, shafts and basement corners are usually hand spray work.

• Volume. A robotic rig can require extra site infrastructure set-up. A few cubic metres of detail work does not usually justify it. A continuous in cycle heading does.

• Steel. Congested reinforcement on a retention wall is encapsulated more reliably by hand.

• Unsupported ground. The operator stays back under supported ground while the boom works forward.

• Finish. A wall that has to finish to profile and hand trowelled surface, is typically hand sprayed and cut back.

On most tunnelling projects both can run side by side. The rig sprays the lining and the hand crew sprays the connections, the detail and the finish.

Before a job is priced, decide which method each part of the scope needs, then size the compressor, the pump and the crew to that method. A compressor sized for hand spraying only gives a rig about half the air it needs at the nozzle for robotic spraying!

Certification

EFNARC runs the only globally recognised certification scheme that covers both Hand Spraying and Robotic Spraying of sprayed concrete, and it certifies the two as separate categories because they are different competencies. A certificate in one does not cover the other. We deliver both courses with our director and founder, Scott Graham, currently the only EFNARC Examiner in Australia certified for both schemes, who also holds the EFNARC nozzle operator certificates for robotic and hand spraying. The course pages set out the modules and the enquiry form.

We run EFNARC nozzle operator courses for Robotic and Hand Spraying, on your site or at other locations by arrangement. The course pages have the modules and the enquiry form.