Phased shotcrete or gunite is a common procedure especially on large projects and is not uncommon in swimming pools and artificial rock structures. For your information, the 2006 International Building Code (in section 1913.7) permits placing additional shotcrete on previously applied work when the shotcrete edges are sloped to a thin edge. This is required to facilitate the nozzling of subsequent placements and to minimize the risk of rebound entrapment when shooting continues.
The International Building Code also states that before placing additional shotcrete adjacent to previously applied shotcrete, sloping and square edges shall be cleaned and wetted. Wetted means that the receiving surface shall be brought to a saturated surface dry condition. Clean means that the surface must be free of gloss, laitance or other contamination. This can be accomplished by cleaning the joint while it is green on the first day or by cleaning with water blasting, sandblasting, or wire brushing after the surface has hardened. The American Concrete Institute does not recommend the use of bonding compounds for use in shotcrete work because bonding compounds can act as bond breakers and the bond of shotcrete to properly prepared substrates is normally excellent. The International Building Code does not place any limitations on the time between phases of shotcrete application.
Therefore, the phased shotcrete or gunite application in swimming pools and artificial rock structures is acceptable as long as the procedures required by the International Building Code were followed. Further, the phased shotcrete or gunite applications need not take place on the same day or subsequent days.
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