The thickness of the shotcrete placement, site logistics, and the availability of ready-mixed concrete, as well as expertise of the shotcrete contractor would likely determine the most cost-effective method for shotcrete placement. Both dry-mix and wet-mix will produce structural concrete in place with similar physical properties and durability. Wet-mix can generally produce more volume of material placed per hour than dry-mix. You had several basic questions about shotcrete that can be answered by visiting sections of Shotcrete.org. On our website, you will find the informational pages www.shotcrete.org/Resources and www.shotcrete.org/ArchiveSearch beneficial. The Resources page lists many shotcrete-specific articles and web resources. The Archive Search allows you to search through our Shotcrete magazine archive for past articles using keywords. You may also find ACI 506R-16, “Guide to Shotcrete,” an informative primer on all aspects of shotcrete. You can purchase a PDF copy of the Guide from ACI at www.concrete.org/store/productdetail.aspx?ItemID=50616. ACI Committee 506, Shotcreting, also has several other technical documents available for specification for shotcrete, evaluation of shotcrete cores, specifying underground shotcrete, and fiber-reinforced shotcrete you can find on the ACI website.