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It appears you are talking about a nozzleman who has not been pre-qualified by shooting a mockup panel on a specific project. There is no official ASA or ACI document that addresses this issue. However, this situation is similar to what ACI guidance provides regarding ACI-certified Shotcrete Nozzlemen and Nozzlemen-in-training. ACI’s Certification Program Policy for Shotcrete Nozzleman and Nozzleman-In-Training Section 1.04 states: “ACI Shotcrete Nozzleman-In-Training (NIT) certification is available to applicants who do not possess 500 hours of work experience but do possess a minimum of 25 hours of hand nozzling work experience in the process being sought (vertical orientation only). The examiner of record may require an ACI-certified nozzleman to be present during the performance exam; however, the ACI-certified nozzleman’s interaction with the examinee is strictly limited to the safety of the shooting operation.”
Shotcrete is a method for placing concrete. Concrete has a set time that provides hardness of the in-place concrete. Final set may take anywhere from an hour to several hours depending on the concrete mixture and the weather.
Hot weather has a faster set time than cold weather with the same concrete mixture. If the pool is shot in the morning, it may be hard enough to tolerate a rainstorm in the late afternoon. The concrete should certainly be set by the next day unless there is a very cold overnight temperature or a problem with retarder in the concrete mixture. Tarps could be placed over the vertical walls to protect them from a sudden rainstorm. The floor may be harder to protect as the rainwater wouldn’t necessarily drain off the floor.
If concrete is exposed to rain and the surface isn’t washed off in any way, the concrete should be good. Similarly, if you are expecting freezing temperatures overnight, the fresh concrete must be protected from freezing. This may require using vented heaters and insulated blankets. The goal of the cold weather protection is to keep the surface temperature of the fresh concrete above 50°F (10°C). More details on cold weather protection can be found in ACI PRC-306-16 Guide to Cold Weather Concreting available directly from ACI’s bookstore (concrete.org/store.aspx).
By hydration, I’m assuming you are referring to curing of freshly placed concrete. A minimum of 7 days of continuous wet curing is recommended. Continuous means the exposed concrete surface is wet the entire duration. Not just “watered” twice a day as has sometimes been suggested by contractors. Use of a spray-on curing membrane is an option if for some reason water curing is not practical.
If you are looking specifically at swimming pools, this ASA Pool and Recreational Shotcrete Committee Position Statement “Curing of Shotcrete for Swimming Pools” provides more details: shotcrete.org/wp-content/uploads/2022/01/218216_ SCMSummer21_PS7v2.pdf Also, for a more detailed look at curing, the American Concrete Institute (ACI) document, ACI PRC-308-16 Guide to External Curing of Concrete is an excellent reference.
You can find this at ACI’s bookstore (concrete.org/store.aspx). Finally, a good reference on the basics of concrete, from materials to placement and curing, is the Portland Cement Association’s “Design and Control of Concrete Mixtures, 17th Edition.” You can find this on the PCA website bookstore.
