Shotcrete

Procedures for Minor Gunite or Shotcrete Repair in Swimming Pools

Minor gunite repair

Both minor and major repairs, as well as extensive remodeling, are common in existing swimming pool structures. Removal and replacement of portions of a pool structure is perfectly acceptable as long as the procedures listed below are followed for attaining proper bonding of the new repair materials to the existing swimming pool structure.

Voids, low-density areas, weak concrete, or other defects may be encountered in pneumatically applied concrete or mortar in swimming pool construction. Unsuitable shotcrete may be observed visually or located by sounding. When sounded, unsuitable areas may not emit a sharp ringing sound when the surface is hammered with a metal object. In addition, “rebound” may have been placed or allowed to remain on the surface in localized areas which often de-laminates from the underlining substrate.

Rebound is typically made up of the larger and harder particles (which tend to ricochet) and does not contain adequate cement, water, or density to develop significant strength. Rebound, therefore, should not be used in any application where strength, hardness, or durability is needed. Rebound is frequently encountered on horizontal surfaces such as the pool floor, shallow end access steps, and the tops of “below water benches”. Rebound on or near the shotcrete surface may become delaminated in the future and must be removed prior to the pool’s plaster surface application.

Unsatisfactory shotcrete can best be removed by the use of lightweight, pneumatic jackhammers which will remove the unsatisfactory shotcrete without damaging the structural shell. These tools are almost self-policing as they are powerful enough to remove unacceptable shotcrete but too lightweight to remove sound shotcrete with any efficiency. In applying this industry accepted technique, the areas of unsatisfactory shotcrete should be chased with the chipping hammer much like how a dentist removes decayed material from a tooth. The full extent of the unsatisfactory shotcrete would be removed in this manner.

The following procedures must be followed for attaining proper bonding of the new repair materials to the existing swimming pool structure.

1. Existing surfaces must be sound, free of defects, clean, and free of bond inhibiting materials.

2. Existing surfaces must be roughened by chipping or other suitable means to provide an open pore structure. All loose, cracked or deteriorated materials must be removed.

3. Clean existing surfaces by water blasting.

4. Saturated surface dry condition of the substrate shall be maintained to prevent premature drying of the bonding paste.

5. Any reinforcement exposed in the repair or remodeling must be completely exposed with a minimum of 1 inch clear completely around the reinforcement to permit proper encasement of the reinforcement in the repair material.

6. Where it is impractical to use pneumatically applied material for the repair, dry pack mortar (low water content) may be used for small repairs to minimize the potential for shrinkage cracking. Pre-packaged products such as Rapid-Set Mortar Mix (for thinner repairs) or Rapid-Set Concrete Mix (for thicker repairs) are low shrinkage, fast setting products formulated for repair applications and are ideal for minor repairs in swimming pool. When using pre-packaged products, it is critical that the manufacturers use limitations, mixing, and placing instructions be explicitly followed.

7. When using Dry Pack Mortar or equivalent, the material should be applied over cement paste or another approved bonding agent, which has been brushed onto the substrate (existing material) for absorption into the pore structure. The new material shall be applied before the cement paste or other approved bonding agent “skins over” or starts its “setting stage”. Bonding aids are generally not required when pneumatically applied materials are utilized in the repair.