How do you spray concrete? Spraying concrete, also known as shotcrete or gunite, involves applying concrete using a high-velocity hose, allowing for efficient placement on surfaces like walls, tunnels, pools, and slopes. There are two main methods for spraying concrete: dry-mix and wet-mix. Here’s a breakdown of both methods:

　　1. Dry-Mix Shotcrete

　　In the dry-mix process, the dry concrete mix （cement, sand, and aggregates） is fed into a spray gun. Here’s how it works:

　　- Step 1: The dry mixture is placed into a hopper and transferred to the nozzle using compressed air.

　　- Step 2: Water is added to the mix at the nozzle as it’s sprayed out, allowing the operator to control the consistency.

　　- Step 3: The concrete is applied in layers as needed. This method allows for adjustments in water content as you go, making it more versatile.

　　Advantages:

　　- Better for vertical and overhead applications.

　　- Allows real-time control of water content.

　　Disadvantages:

　　- Can produce more dust.

　　- Requires skilled operators to control water content.

　　2. Wet-Mix Shotcrete

　　In the wet-mix process, the concrete （already mixed with water） is delivered through a hose. Here’s the process:

　　- Step 1: Ready-mixed concrete is loaded into the pump and pushed through the hose.

　　- Step 2: Compressed air is introduced at the nozzle to accelerate the mix, which is then sprayed onto the surface.

　　- Step 3: Apply in layers as needed, just as in the dry-mix method.

　　Advantages:

　　- Less dust and rebound, making it safer.

　　- Easier to achieve consistent quality since the concrete is pre-mixed.

　　Disadvantages:

　　- Limited control over water content.

　　- Requires a wet-mix concrete pump, which can be costly.

　　General Tips for Spraying Concrete

　　- Surface Preparation: Clean and wet the surface before spraying to improve adhesion.

　　- Application Technique: Keep the nozzle at a consistent angle （usually 90°） and distance （often 2-3 feet） from the surface.

　　- Layering: Apply in layers, allowing each to set slightly if applying multiple layers for thicker coverage.

　　- Curing: After application, keep the sprayed concrete moist for a few days to ensure proper curing and strength development.

　　Sprayed concrete can be used in both structural and aesthetic applications, and it’s particularly valued for its versatility in forming shapes and reinforcing surfaces.