A skilled, knowledgeable nozzleman with properly functioning equipment and suitable materials is the key to good shotcreting.
Shotcreting equipment should be designed and maintained to provide a smooth flow through the hose to the nozzle and then to the work surface. Hose should be of good quality, gum-lined and wrapped. The air compressor should have sufficient capacity. Scaffold should be provided that will permit the nozzleman to move close enough when necessary to shoot reinforcing steel yet at other times to get back far enough to shoot smoothly.
GENERAL PLACING TECHNIQUES
In normal operation the nozzle stream is perpendicular to the plane of application. The nozzle should be moved continuously in a circular motion but always kept perpendicular to the surface--not waved back and forth or up and down, changing the angle of impact. Waving the nozzle increases rebound and overspray and makes a rougher surface. Even with good technique, slugs of insufficiently wet material may occasionally be deposited. Such material should be cut from the work.
MINIMIZING SANDPOCKETS FROM REBOUND AND OVERSPRAY
Aggregate, cement and water that does not adhere to the point of application but falls somewhere else by gravity is known as rebound. If it is not removed and gets covered with good shotcrete it becomes a conduit for water that can cause deterioration due to freezing and thawing.
The compressed air in the spray is intended to escape freely from the surface on which the shotcrete is deposited but it inevitably carries some of the cement, aggregate and water away with it, spreading out perpendicular to the nozzle stream in all directions parallel to the surface of application. This material is known as overspray, a low-quality material that is not shotcrete; it should be either avoided or removed.
The greatest skill and closest attention must be given to encasing such items as pipes, inserts and particularly reinforcing steel.