Repair, Troubleshooting, and Rework
Troubleshooting dry-mix shotcrete means diagnosing symptoms and correcting root causes. Common problems include dust and dry pockets (too little water, worn water ring, low water pressure), sagging or sloughing (too much water, layer too thick, accelerator issues), surging or slugs (low air, hose kinks, moisture in the line), high rebound (air pressure too high, nozzle angle or distance wrong, mix too dry), and poor bond or delamination (inadequate surface prep, cold joints, trapped rebound).
Repair work requires removing defective material to sound substrate, squaring edges, cleaning and pre-wetting, then rebuilding with proper technique. Don't cover over voids or delamination; investigate and remove them. Document the defect, the cause, and the corrective action. Rework should follow the same quality controls as original placement, including test panels where appropriate.
Traps: adding water to fix surging (the cause is usually air or hose issues); patching over unsound material; assuming rebound trapped behind reinforcement is acceptable; skipping documentation.
Worked example / rule of thumb: when the stream surges, check air supply, hose kinks, and moisture in the line before touching the water valve. For delamination, sound the area, remove all unsound material to a firm base, prepare the surface, and rebuild in controlled layers with the same QC as new work.