I am a homeowner who is having a pool built in my backyard. The company used shotcrete last Thursday, but didn’t tell us we needed to keep it wet for the next few days. We found out on the following Monday that we should have been keeping the shotcrete wet. The 4 days that passed before we began wetting the shotcrete were very windy and hot (low 80s). The pool company is now telling us that it’s probably not a big deal that the shotcrete wasn’t kept wet for 4 days. My question is this: How has the shotcrete been compromised by not keeping it wet for 4 days? What can I expect to happen to the shotcrete (cracks?) What would you recommend as far as a fix??

ASA recommends a minimum of 7 days curing to help control shrinkage issues in young concrete sections. Lack of curing, and exposure to windy, hot or dry conditions will certainly increase the potential for shrinkage and cracking of the concrete. Lack of curing will prevent the concrete from achieving its maximum potential strength. However, shotcrete generally exceeds the minimum 4000 psi (28 MPa) 28-day compressive strength ASA recommends, and required strength depends on the pool design. If you want to confirm the compressive strength of your in-place concrete, cores taken from the pool should be tested for compressive strength by a qualified testing lab. ASTM C1604 Standard Test Method for Obtaining and Testing Drilled Cores of Shotcrete gives guidance on taking cores from existing structures. A minimum 3” diameter core is recommended. Before coring it is recommended to use ground penetrating radar (GPR) or similar equipment to identify the location of reinforcing in the pool section, and then take cores to avoid cutting through the reinforcing wherever possible. The core holes would then need to be filled with a high strength, non-shrink cementitious grout. Once you learn the actual strength, you would need to check with the pool design engineer to verify the strength is adequate for the design. If the strengths are not adequate, you should consult with the pool designer or a licensed professional engineer experienced in pool design for potential solutions.