We are shotcreting our first wall and the contractor tells us that in shotcrete, the lapping of the bars is not done by putting the bars alongside each other as in conventional pouring of concrete but rather a gap is left between the bars in order to avoid voids behind bars bundles. A two-inch gap is being used on our job. Is there a publication that deals with reinforcing steel placement in shotcrete in general and one that deals with bar laps in particular?

The ACI 506R-90 Guide to Shotcrete, Section 5.4.2 is the publication you are looking for. Amongst other things it states: “If the design allows, lapping of the reinforcing splices should be avoided. Lapped bars should be spaced apart at least three times the diameter of the largest bar at the splice”. If laps are not permitted by the design, then it is best to lap the bars one on top of the other (relative to the shooting orientation), rather than side-by-side, to facilitates proper encapsulation with shotcrete.