The easy answer is that shotcrete material is the same as concrete material and that the same rules or guidelines would apply to shotcrete as to concrete. We usually tell our customers to present this question to the painters. The curing process and chemical reactions are greatest in the first 28 days. Generally a paint or coating is not applied until after the curing of the shotcrete is complete, or mostly so, and the moisture content of the shotcrete is below a point specified by the coating manufacturer.