Shotcrete is just a placement method for concrete. Thus, the in-place material will have the same characteristics as concrete. You should consult the coating supplier to establish how long they want the concrete surface cured. They may also specify a certain limit for surface moisture conditions. There are several methods for evaluating the moisture content of the in-place concrete. Here are the ASTM standards that deal with surface moisture:
- ASTM F710, Preparing Concrete Floors to Receive Resilient Flooring; Section 5.2, pH Testing;
- ASTM F1869, Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride;
- ASTM F2170, Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes;
- ASTM F2659, Preliminary Evaluation of Comparative Moisture Condition of Concrete, Gypsum Cement and Other Floor Slabs and Screeds Using a Non-Destructive Electronic Moisture Meter; and
- ASTM F3191, Field Determination of Substrate Water Absorption (Porosity) for Substrates to Receive Resilient Flooring.
In addition, The International Concrete Repair Institute (ICRI) has a certification program, “ICRI Concrete Slab Moisture Testing Technician—Grade 1.”