I have been in the swimming pool industry for 30 years and I deal with a lot of different engineers on my commercial projects who want a wet test to verify water tightness before the finish is applied to the pool. In my experience, air-entrained shotcrete tends to be porous and leak. Are there any engineering specifications that state that air-entrained shotcrete is porous and will leak if the surface is not trowel-finished?

Properly added and mixed air-entraining admixture in concrete will actually reduce the permeability of concrete. This is because the small, well-formed air bubbles from air-entraining admixtures are not interconnected as larger, entrapped air bubbles may be in non-air-entrained concrete. Thus, the reported higher permeability of the air-entrained shotcrete is not a material flaw but must be from poor shotcrete application. Air entraining from 4 to 7% air is advantageous for enhanced resistance to the freezing-and-thawing cycles of saturated concrete and should be specified by the designer in areas subject to significant numbers of freezing-and-thawing cycles annually. The reported high permeability and resultant failure to pass a water-tightness test could be investigated by taking cores of the “porous” material and conducting a petrographic analysis of the core. Based on the reported results, I strongly suspect that the in-place shotcrete has major issues with sand pockets, overspray, and rebound.