Shotcrete Calculator

1. Enter the area to cover and its unit, and the in-place thickness in inches.
2. Choose the process (wet-mix or dry-mix) and the orientation (vertical or overhead).
3. The calculator sets a typical rebound allowance; override it if you have a figure from your applicator.
4. Read the shotcrete to order, the in-place volume and the rebound allowance.

Here is what each result means:

Shotcrete is concrete sprayed at high velocity onto a surface, used for pools, walls, tunnels, slopes and repairs. It needs no formwork on the back face, which is why it suits curved and vertical work.

When shotcrete hits the surface, some of the material bounces off and is lost. That loss, called rebound, means you must order more than the in-place volume. How much more depends mainly on the process: dry-mix (sometimes called gunite) rebounds more than wet-mix, and overhead work rebounds more than vertical. This calculator adds that allowance so your order covers the finished thickness.

The in-place volume is area times thickness, converted to cubic yards. The order volume is that plus the rebound allowance, which is a percentage set by the process and orientation.

1. Multiply the area by the thickness in feet for the in-place volume, and divide by 27 for cubic yards.
2. Take the rebound percentage for the process and orientation, or your own figure.
3. Multiply the in-place volume by one plus the rebound fraction for the order volume.

Suppose you are shooting a wet-mix wall of 1,000 square feet at 4 inches thick, with the default 10 percent rebound for vertical wet-mix.

Calculation: in-place volume = 1,000 x (4 / 12) = 333 cu ft = 12.35 cu yd. With 10 percent rebound, order 12.35 x 1.10 = 13.58 cu yd, so the allowance is about 1.2 cu yd.

The same wall shot dry-mix overhead could lose 35 percent, pushing the order to about 16.7 cu yd, which is why the process and orientation matter so much.

The process is the biggest driver of rebound. The table shows typical ranges; the calculator uses a mid-range default you can override. ACI 506R puts overall losses at roughly 10 to 30 percent.

Wet-mix rebounds less and wastes less material, while dry-mix can suit repairs and variable thickness. Overhead work always rebounds more than vertical.

Process and Orientation

Dry-mix and overhead work rebound the most; wet-mix on a vertical face the least. These set the default here.

Reinforcement

Shooting through wire mesh or rebar, especially if it is not well anchored, raises rebound as material bounces off the steel.

Layer Thickness and Nozzle Technique

Thin layers and a poor nozzle angle or distance increase rebound. A skilled nozzle operator cuts it substantially.

Mix and Aggregate

Aggregate size and grading, and the mix design, all affect how much material sticks versus bounces off.

Ordering Sprayed Concrete

Size the order for a pool, wall, tunnel or slope so it covers the thickness after rebound.

Comparing Processes

See how much more material a dry-mix job needs than a wet-mix one for the same area and thickness.

Checking an Applicator Quantity

Sanity-check a quoted volume against your area, thickness and a realistic rebound figure.

1. Ignoring Rebound

Ordering only the in-place volume leaves you short, because a real part of the material bounces off. Always add the allowance.

2. Using One Rebound Figure for Every Job

Dry-mix overhead can lose three times what wet-mix vertical does. Match the figure to the process and orientation.

3. Forgetting Reinforcement

Shooting through mesh or rebar adds rebound. Nudge the figure up for heavily reinforced work.

4. Measuring the Wrong Thickness

Use the specified in-place thickness, not the sprayed-on build-up, so the finished layer is right.

5. Treating the Estimate as Exact

Rebound depends on the operator and conditions. Confirm the allowance with your applicator.

The volume arithmetic is exact; the rebound allowance is a typical figure, not a measured one for your job.

Multiply the area by the thickness for the in-place volume, convert to cubic yards, then add a rebound allowance. For 1,000 square feet at 4 inches with 10 percent rebound, that is about 13.6 cubic yards to order.

Rebound is the material that bounces off the surface during spraying and is lost. It means you order more than the in-place volume. Wet-mix rebounds less, dry-mix more, and overhead work more than vertical.

Roughly 5 to 15 percent for wet-mix and 20 to 40 percent for dry-mix, with overhead at the higher end. ACI 506R gives an overall range of about 10 to 30 percent. Use a figure from your applicator when you have one.

Both are sprayed concrete. Gunite is the dry-mix process, where water is added at the nozzle; wet-mix shotcrete is batched with water and pumped. Dry-mix generally rebounds more.

Yes. It adds a rebound allowance based on the process and orientation you choose, and you can override it with your own percentage.

It depends on the application and the specification, from an inch or two for linings up to several inches for structural walls and pool shells. Use the specified in-place thickness.

Gravity works against overhead placement, so more material falls away before it bonds, raising rebound. The calculator uses a higher default for overhead work.

Yes. Spraying through mesh or rebar increases rebound, especially if it is poorly anchored. Add a few points to the rebound figure for heavily reinforced work.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• American Shotcrete Association (ASA; shotcrete process and rebound).
• National Ready Mixed Concrete Association (NRMCA; concrete materials).
• American Cement Association (Portland Cement Association) (American Cement Association; concrete basics).
• QUIKRETE concrete and bag calculator (QUIKRETE; volume and yield method).