Because shotcrete is a placement method for concrete, standard concrete repair techniques are applicable. If the repair is being done by shotcreting new concrete on the existing concrete, the repair should include these steps:
- Chip the poor or weak concrete back to sound concrete.
- If reinforcing bars are exposed, they should be cleaned of any rust.
- If more than half of the perimeter of a reinforcing bar is exposed, the concrete should be chipped back to provide at least a 0.75 in. (19 mm) space behind the bar to allow shotcrete to flow around the back of the bar.
- Before shooting any additional shotcrete, the surface should be cleaned and then wetted to a saturated surface-dry condition (SSD).
- SSD means the substrate is damp, but there is no flowing water. It should feel damp to the touch, but no water is picked up on your hand when placing it against the surface.
- Do not use bonding agents, as they can interfere and reduce the bond of the new shotcrete to the old shotcrete surface.
- When the new shotcrete is in place, the contractor should initiate water curing as soon as possible. In warm, dry, or windy weather, fogging of the fresh surface immediately after finishing would be helpful.
- Water curing (where the concrete is kept continuously moist) should be supplied for at least 7 days.