Mix design and control are critical to the success of a shotcrete product. The specified mix should reflect the desired "in-situ" requirements for both initial and final support. When an emphasis is placed on mix design, material handling equipment, and correct pre-testing prior to producing the shotcrete, problems should be minor. Shotcrete should run smoothly as long as monitoring of the process by core sampling and test panels take place throughout the length of the job. Typically, mix contains a 30 percent cementitious material and 70 percent sand and aggregate. Both should be well graded and screened because just one rock can clog a shotcrete hose and halt an entire operation. Slump should be as low as possible depending on distance and pumpability. Plasticisers and water reducing agents should also be used to modify slump depending on working conditions. The mix will normally be pumped into a 2 inch shotcrete hose to be applied via a robotic arm or hand-held nozzling. A good pump easily performs 15-25 cubic yards per hour, and with proper setup, quality control and maintenance, the shotcrete process can be continuous.