Surface Preparation and Placement
Successful shotcrete depends heavily on surface preparation and placement technique. Surfaces must be sound, clean, and free of loose material, dust, oil, form release agents, and standing water. Concrete substrates typically require roughening (chipping, scarifying, or abrasive blasting) to promote mechanical bond, and existing surfaces should be pre-wetted to a saturated-surface-dry condition so the new shotcrete does not lose water to the substrate. For overhead and vertical work, initial layers are applied thinly and built up; reinforcement must be positioned so shotcrete can encase it without voids, especially on the far side of the bar.
Traps: candidates confuse pre-wetting (saturate but no free water) with wetting that leaves puddles, which weakens the bond. Questions often test encasement of reinforcement-nozzleman angle and distance should allow material to pack behind the bar; shadowed areas must be filled. Also, cold joints and construction joints require proper preparation before the next layer. Thickness control, shooting from bottom to top on walls, and avoiding overspray onto finished surfaces are common inspection points.
Rule of thumb: prepare, clean, and pre-wet to SSD before shooting; build up in controlled layers; and never shoot over rebound, dust, or free water-bond failure is the most common placement defect.