Homeowner’s Guide to Shotcrete in Pool Construction

What Is Shotcrete?

Shotcrete is pneumatically applied concrete (sprayed at high velocity) to form strong, watertight, and highly customizable structures like swimming pools. It comes in two main types:

• Wet-mix: Ready-mixed concrete pumped to the nozzle

• Dry-mix (Gunite): Dry materials are conveyed to the nozzle and with added water or hydrated at the tip

When applied correctly, shotcrete creates a monolithic pool shell — seamless and structurally sound.

Certification Matters: The ASA/ACI  Nozzleman Program

A quality shotcrete application starts with the person holding the nozzle. The American Shotcrete Association or ASA, has a Certified Nozzleman program that ensures that nozzle (hose) operators are tested and qualified in addition, the American Concrete Institute or ACI has created specific guidelines and construction standards to ensure the process is compliant with the building standards of :

• Specific shotcrete process: Wet-mix or Dry-mix

• Shooting positions: Vertical, Overhead, or Encased

What the Certification Involves

1. Minimum 500 hours of nozzle experience

2. Written exam: Covers shotcrete theory, rebound control, nozzle technique, curing, etc.

3. Performance exam: The candidate shoots a panel, which is cored and tested in a lab for proper strength, density, and steel encapsulation

4. Certification is valid for 5 years, issued by ACI, and listed in their public database.

Tip for Homeowners:
Ask your pool builder for proof of ASA/ACI nozzleman certification. It’s the most important credential in the shotcrete process as part of the pool construction.

Shotcrete Strength & Quality Standards

Minimum Requirements

• Compressive strength: ≥ 4,000 psi after 28 days

• Water-to-cement ratio: ≤ 0.45 (low permeability)

• Curing: At least 7 days (wet or with curing compounds)

• Installation Temperatures between 50℉ and 90℉

Tools of Quality

• Use of air lance during application to remove rebound
• Removal of rebound (loose) material from coves, walls, and floor transitions (never re-use)
• Shotcrete is applied to a stable, rigid substrate.

Steel Reinforcement: Ratios, Placement, and Clearance

ACI Steel-to-Concrete Ratios (Minimums)

• Per ACI 318, the minimum shrinkage/temperature steel ratio is 0.0018 (0.18%) of concrete cross-section

  • For a 6" wall, this equals ~0.26 in² of rebar per foot

  • Common spacing: #3 or #4 bars @ 6"–8" O.C.

Rebar Placement & Coverage

• Steel must be fully encased in shotcrete with:

  • 3" soil clearance below and 2" min above the steel or between PVC - plumbing

  • Double curtain reinforcement for thicker walls or spas that are raised from the ground

• The concrete cover must meet ACI 318 standards:

  Surface	Minimum Cover
  Soil-exposed surfaces	3"
  Formed surfaces (walls)	2"
  Interior (non-soil contact)	1½"–2½"

• Too little steel or poor coverage leads to cracking, corrosion, and structural failure.

• Tip for Homeowners:  Prior starting the application the pool should be cleaned and have no water or mud specially touching the steel in walls or in the floor. When in dry climate the soil should be slightly wet (Surface Saturated Dry) to receive the shotcrete.

Concrete Shrinkage vs. Structural Cracks

Concrete naturally shrinks as it cures. Understanding the difference between shrinkage cracks and structural cracks is key:

Shrinkage cracks are generally not a concern when they are small; however, structural cracks, small or large may lead to leaks (weep holes) and rebar exposure, necessitating repair. Always have an expert assess any cracking.

Application Techniques: Air Lance and Rebound Control

A second worker must accompany the nozzleman to operate an air lance, which:

• Clears rebound material from tight transitions

• Helps bond layers and remove dust

• Ensures full encapsulation of rebar

Rebound material (shotcrete that bounces off during application) must never be reused. It’s structurally inferior and can cause voids and cracking. 

At J Designs, we actively implement these and other techniques to ensure our pools perform as designed. We install our floors 3 to 5 days before shooting the rest of the pool. This method helps prevent loose material from falling onto the floor, which makes it harder to remove, especially when a lot of steel is present. Additionally, vibrating the concrete helps maintain the steel encapsulation in observance of the building code and the engineer's requirements.

The Importance of Curing (Watering)

Shotcrete must be kept moist for at least 7 continuous days (minimum non-negotiable) multiple times per day using:  Keeping the concrete at a controlled temperature and wet helps the concrete paste to harden at a slower rate, avoiding shrinkage and allowing the curing to be most effective resulting in a stronger structure.

• Typically used in this process: Mist sprays, soaker hoses, wet burlap, and hand watering.

Improper curing leads to surface scaling, poor strength, and increased risk of cracking.

Tip for Homeowners:  Spray all pool areas thoroughly 3 times a day for 5 to ten minutes.

Homeowner Checklist

Summary Table

A shotcrete pool is only as good as the standards followed during construction. The Los Angeles Building Department published the Information Bulleting—Building Code regarding Wet-Mix Shotcrete, which is enforceable with the standards for any shotcrete installation. Read the complete bulletin here: LADBS Bulletin—Code.

With certified personnel, proper reinforcement, careful curing, and full adherence to ASA and ACI guidelines, your pool will be beautiful and built to last for generations. Check these two articles below about the most critical process in pool construction.

Preventing Weepers

Shotcrete VS Gunite