Shotcrete is a fast, flexible way to place concrete where traditional pouring and formwork are impractical. This innovative method can deliver efficient, strong, and durable results, even in confined spaces and on irregular substrates.
But where does shotcrete perform best, and how does it compare with poured concrete? In this guide, our specialists explain what shotcrete is, its key benefits, common applications, and application process.
Key takeaways
- Shotcrete is a method whereby mortar or concrete that’s sprayed directly onto a surface.
- It is best suited to projects where access, surface shape or formwork requirements make conventional concrete placement difficult.
- Its main advantage is flexibility, allowing concrete to be placed efficiently across vertical, overhead and irregular areas.
- The choice between wet-mix and dry-mix shotcrete depends on factors such as project scale, production needs and site conditions.
- Compared with poured concrete, shotcrete can reduce formwork and simplify construction on complex or restricted sites.
- It has broad uses across tunnelling, ground support, retaining works, repairs, pools and architectural concrete.
- Good results depend on more than the material itself. Surface preparation, nozzle technique, reinforcement, finishing and curing all influence performance.
- Shotcrete is not automatically stronger or cheaper than poured concrete. The better option depends on the design, geometry, access, labour and construction method.
What is shotcrete and how does it work?
Shotcrete is a sprayed concrete or mortar that is pneumatically projected at high velocity through a hose and nozzle onto a prepared surface.
Rather than being poured into conventional formwork, the material is sprayed into position and compacted by the force of impact, allowing it to bond closely to vertical, overhead, curved and irregular surfaces.
This application method makes shotcrete well suited to projects where access, geometry or ground conditions make conventional concrete placement difficult.
There are two main shotcrete processes: dry-mix and wet-mix. The key difference is when water enters the concrete mixture.
Dry-mix shotcrete
With dry-mix shotcrete, also known as gunite, the dry or slightly damp cementitious materials and aggregates travel through the delivery hose using compressed air. Water is introduced at the nozzle immediately before the material is sprayed onto the surface.
Because the nozzle operator controls the water addition during spraying, dry-mix shotcrete offers flexibility during placement. It can suit smaller-volume works, concrete repairs and applications that involve frequent starts and stops.
Wet-mix shotcrete
With wet-mix shotcrete, the cement, aggregates and water are mixed before the concrete enters the delivery equipment. The concrete is pumped to the nozzle, where compressed air accelerates it onto the receiving surface.
This type of shotcrete supports consistent mix proportions and higher production rates, making it particularly suited to larger-volume projects such as tunnels, retaining structures, slope stabilisation and major civil works.
Shotcrete vs poured concrete
| Factor | Shotcrete | Poured concrete |
| Placement method | Sprayed at high velocity through a hose and nozzle directly onto the receiving surface. | Placed into prepared formwork, then consolidated to help remove entrapped air and fill the form. |
| Mixing | Wet-mix shotcrete is mixed before pumping. Dry-mix shotcrete carries dry or slightly damp materials through the hose, with water added at the nozzle. | Concrete is fully mixed before it is placed into the formwork. |
| Formwork | Can reduce the amount of conventional formwork required, particularly on vertical, curved and irregular surfaces. | Generally relies on formwork to contain and shape the concrete until it gains sufficient strength. |
| Strength | Can achieve high structural strength and durability when correctly designed, applied and cured. High-velocity placement compacts the material against the surface. | Can also achieve high structural strength and durability when properly designed, placed, consolidated and cured. |
| Best suited to | Tunnels, retaining walls, slopes, structural repairs, overhead work and complex or irregular profiles. | Slabs, footings, beams, columns and other structures with predictable shapes and straightforward formwork. |
| Access and geometry | Well suited to restricted-access areas and surfaces that are difficult to form using conventional methods. | Often more practical where there is enough access to install, support and remove formwork efficiently. |
| Construction efficiency | May reduce forming work and simplify placement on complex structures, helping shorten construction time in suitable applications. | Can be highly efficient for repetitive or simple structures where formwork is easy to build or reuse. |
| Cost considerations | Requires specialised equipment and experienced nozzle operators, but reduced formwork and labour can improve overall project efficiency. | Often cost-effective for simple, repetitive construction, although complex formwork can increase labour and material costs. |
Shotcrete and poured concrete use the same basic ingredients: cementitious materials, aggregates and water. The key difference isn’t the composition, but how it’s placed.
Shotcrete is sprayed at high velocity through a nozzle, while poured concrete is placed into formwork and then consolidated, usually by vibration.
Both methods can produce strong, durable concrete when correctly designed, placed and cured. Shotcrete is especially useful for vertical, overhead, curved and irregular surfaces, while poured concrete is often better suited to slabs, footings, columns and other structures with straightforward formwork.
Let’s take a closer look at the other core differences between these techniques:
Mixing
Poured concrete is mixed before placement. Wet-mix shotcrete is also mixed before pumping, whereas dry-mix shotcrete carries dry or slightly damp materials through the hose and introduces water at the nozzle.
Formwork
Poured concrete generally needs formwork to contain and shape the fresh concrete until it gains sufficient strength. Where shapes are complex or access is restricted, constructing and removing these forms can add considerable labour and time.
Unlike traditional concrete, shotcrete reduces the need for conventional formwork because crews spray the material directly onto a receiving surface.
This pneumatically projected concrete can make construction faster and simpler on retaining walls, tunnels, slopes and structures with curved or irregular profiles.
Strength
While both shotcrete and poured concrete can achieve high structural strength, they do so in different ways.
Shotcrete strikes the receiving surface at high velocity, compacting to form a dense layer on suitable substrates. This makes it particularly effective for structural repairs, ground support and concrete placed against irregular surfaces.
Meanwhile, poured concrete relies on proper placement and consolidation to remove entrapped air and ensure the concrete fills the formwork and surrounds reinforcement.
Application
Shotcrete gives crews greater flexibility when working on difficult shapes and surface orientations. The nozzle operator can build concrete up in layers across vertical, overhead and curved areas without relying on full conventional formwork.
On the other hand, poured concrete is placed into prepared forms, making it highly effective for predictable shapes such as slabs, footings, walls, beams and columns.
The best method depends on the structure, site access, geometry, finish requirements and construction sequence.
Cost
Neither method is universally more cost-effective. The final cost depends on factors such as project size, site access, formwork, labour, equipment, concrete volume and construction time.
Poured concrete is often more economical for simple, repetitive structures where formwork is easy to build and reuse. For irregular, vertical or hard-to-access work, shotcrete may offer the more efficient overall solution.
While this technique requires specialised equipment and experienced nozzle operators, it can reduce formwork and simplify construction in difficult locations.
Common shotcrete applications
Shotcrete is typically used for tunnel support, excavation retention, slope stabilisation, retaining structures, concrete repairs, pools and free-form construction.
Mines, tunnel walls and underground construction
Shotcrete provides ground support during tunnel, mine and underground works.
Crews can apply it to exposed rock or ground soon after excavation, either as part of temporary support or as a component of the permanent lining system.
Depending on the design, shotcrete may work with rock bolts, mesh, fibres and other reinforcement to control ground movement and support the excavation.
Excavation support and ground retention
Shotcrete is widely used as a facing for soil nail walls, anchored excavations and other ground retention systems.
Applied to the exposed excavation face, it forms a reinforced facing that works with the designed nails, anchors or reinforcement to support the retained ground.
This approach is particularly useful for deep excavations, basement construction and restricted sites where building conventional retaining walls may be difficult.
Slope stabilisation
Shotcrete can form part of an engineered slope stabilisation system for exposed soil and rock faces.
It provides a protective facing and can work with soil nails, rock bolts, mesh, anchors and drainage measures to improve slope stability.
Because crews can spray it directly against uneven surfaces, shotcrete suits road cuttings, embankments and other slopes where conventional concrete placement is impractical.
Retaining walls and piled wall facings
Shotcrete can create structural retaining walls or provide a continuous facing over piles and other retention systems.
Its spray application allows concrete to follow the profile of the structure while reducing the need for conventional two-sided formwork.
Shotcrete is often considered where excavation space is limited, wall geometry varies or access makes traditional concrete placement difficult.
Concrete repairs and rehabilitation
Shotcrete provides an efficient way to replace deteriorated or damaged concrete without recasting an entire element.
After the substrate has been properly prepared, crews can spray new concrete onto vertical and overhead surfaces to restore the required profile and provide a durable repair.
Applications include bridges, tunnels, retaining structures, marine infrastructure and other concrete assets requiring repair or rehabilitation.
Concrete pool construction
Shotcrete is well suited to swimming pools because it can form walls, floors, curves and transitions as a continuous concrete shell.
The nozzle operator can follow complex profiles without relying on extensive conventional formwork, giving designers greater freedom over the finished shape.
The same placement advantages can be useful for selected tanks, reservoirs, canals and other water-retaining structures when shotcrete forms part of an appropriately designed and detailed system.
Architectural and free-form structures
Shotcrete can create shapes that are difficult or costly to achieve with conventional formed concrete. Crews can build up material over reinforcement to produce curves, contours and detailed three-dimensional profiles.
This makes the method useful for architectural shotcrete, simulated rock, sculptures, skate parks, climbing walls, water features and themed environments where both structural performance and shape are crucial.
The key benefits of shotcrete
The main advantages of shotcrete include reduced formwork, efficient placement, strong bond to suitable substrates, easier access to difficult work areas and the ability to follow complex shapes.
When correctly designed, applied and cured, this method is favoured for its:
Less formwork
One of shotcrete’s main advantages is that it can reduce the amount of conventional formwork required. Because the concrete is sprayed straight onto a receiving surface, complex two-sided forms are often unnecessary.
This can save time, labour and materials, particularly on retaining walls, tunnels, slopes and structures with curved or irregular profiles.
Efficient placement
Shotcrete combines concrete placement and compaction into a single spraying process. The material is applied in controlled layers, allowing crews to cover large or irregular areas without following the same pouring sequence required for conventionally placed concrete.
On suitable projects, this can shorten construction programs and reduce the work associated with formwork, making shotcrete particularly useful for tunnels, ground support and repair works.
Strong adhesion and structural integrity
High-velocity application helps shotcrete form a close bond with a properly prepared receiving surface for excellent strength and durability.
This is one reason it’s widely used for concrete repairs, strengthening works and applications where new concrete must follow an existing structure or irregular substrate.
The quality of that bond still depends on correct surface preparation, suitable materials, good application technique and proper curing.
Flexible shapes and profiles
Shotcrete can follow curved, uneven and complex profiles that may be difficult to achieve with traditional methods. Material can be built up around reinforcement and shaped progressively to suit the required geometry.
This flexibility makes it well suited to tunnels, pools, retaining structures, skate parks, simulated rock and other architectural or free-form concrete applications.
Easier access to difficult areas
Concrete does not always need to be delivered directly beside the workface when shotcrete is used. Pumps and hoses can transport the material to confined, elevated, underground or otherwise difficult-to-reach areas.
This can make placement more practical in tunnels, mines, under bridges, on steep slopes and at restricted-access sites where conventional concrete equipment or formwork may be difficult to position.
Fewer materials and temporary works
Using less conventional formwork can also reduce the timber, steel and other temporary materials required during construction.
On projects with complex geometry, this may lower material waste and labour costs associated with building and stripping forms.
How to apply shotcrete
Shotcrete is generally applied in six stages: surface preparation, reinforcement and set-out, mixing and delivery, spraying, finishing and curing.
The exact process varies by project, but here’s the general process for achieving a dense, well-bonded result.
1. Surface preparation
The receiving surface must be stable, sound and free from anything that could affect adhesion. Preparation may involve removing loose concrete, rock, soil, dust, oil, vegetation or other contaminants.
For repair work, deteriorated concrete may need to be removed and the remaining surface cleaned and roughened. Ground engineering projects can require scaling, trimming, drainage or other preparation before spraying begins.
2. Reinforcement and set-out
Where required by the design, reinforcement is installed before shotcrete application. This may include reinforcing bars and steel mesh, along with ground-support elements such as soil nails, rock bolts or anchors.
Depth pins, screed wires or guides may also be used to control the final thickness and profile. Reinforcement must be positioned so the shotcrete can properly surround it without trapping rebound or leaving voids.
3. Mixing and delivery
The delivery process depends on whether wet-mix or dry-mix shotcrete is used.
With wet-mix shotcrete, the concrete is mixed before being pumped through the hose. Compressed air at the nozzle then accelerates it towards the receiving surface.
With dry-mix shotcrete, often called gunite, dry or slightly damp materials travel through the hose using compressed air, with water added at the nozzle. The nozzle operator controls the water addition during spraying.
4. Spraying and layer build-up
The nozzle operator sprays the material at high velocity, compacting the shotcrete as it strikes the surface. The concrete is progressively built up to the thickness and profile required by the design.
Careful nozzle technique is particularly important around reinforcement, corners and changes in geometry. Loose rebound and overspray must also be managed so they do not become trapped within the finished work.
Where multiple layers are required, loose material, rebound, overspray or laitance that could affect the bond must be removed before the next layer is applied. Hardened surfaces may also require further preparation before spraying continues.
5. Finishing
The required finish depends on the application. Tunnel support, slope stabilisation and some structural works may retain an as-sprayed finish, while other projects require the surface to be screeded, trimmed, floated, trowelled or shaped.
Architectural shotcrete can involve further detailing to create curved profiles, textures or simulated rock finishes.
6. Curing
Like conventionally placed concrete, shotcrete needs appropriate curing after application. Maintaining suitable moisture and temperature conditions allows cement hydration to continue and helps the concrete develop its specified strength and durability.
Depending on the project, curing may involve water, wet coverings, curing compounds or another approved method. Proper curing also helps limit early moisture loss and shrinkage cracking.
Shotcrete for construction projects in Australia and the Asia Pacific
Shotcrete gives engineers and contractors a practical alternative to conventional concrete placement when access, geometry or formwork make construction more difficult.
To achieve lasting results, proper application is essential. The RIX Group is at the forefront of shotcrete application across Australia and the Asia Pacific. From structural works to architectural finishes, our multi-skilled specialists spray over 30,000m3 of shotcrete every year.
Contact us to discuss our proven solutions for your next project.