Structural and base materials · Concrete & Cement
Sprayed Concrete (Shotcrete)
Describes sprayed concrete as a placement method, wet process or dry process, that produces a distinct material condition, and sets out what the method demands of the operator and the receiving face.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What sprayed concrete is
Sprayed concrete is not so much a separate material as a way of placing one. A cementitious mix is projected through a nozzle at high velocity onto the receiving surface, where the impact itself does the compacting. That removes the need for formwork and for vibration, which is precisely why the method is used on faces that would be awkward or impossible to form.
There are two processes. In the wet process the mix is batched with its water, pumped to the nozzle, and air is introduced there to accelerate it. In the dry process a dry or damp mix is conveyed by air and the water is added at the nozzle, an arrangement long known in the trade as gunite. The wet process gives more control over the mix as delivered, while the dry process lets the nozzle operator vary consistency as work proceeds.
Because material is thrown rather than placed, some of it bounces off. That rebound, the layered way material builds up, the shadowing that reinforcement can cause behind bars, and the operator's angle and distance to the face all mean the finished quality depends heavily on the skill of the nozzle crew. Fibres are often used instead of, or alongside, fixed mesh for the same reason.
Terminology
Common names and aliases
These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.
- Shotcrete (US usage)
- Gunite
- Sprayed mortar
- Wet-process sprayed concrete
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Linings to excavations, basements and retaining faces where formwork could not realistically be erected.
- Slope and embankment stabilisation on cut faces and around existing structures.
- Swimming pool and water feature shells formed to curved profiles without formwork.
- Repair and strengthening of existing concrete, where a face is built back up in layers.
- Underpinning and temporary support works carried out in sequence under engineering direction.
- Curved, domed and free-form shapes where conventional shuttering would be difficult to build.
Consideration
Where it is commonly considered
- Where the receiving face is irregular, curved, or accessible only from one side.
- Where erecting and striking conventional formwork would be impractical or unsafe.
- In basement and retaining works carried out in stages under engineering direction.
- Where an existing concrete face is being built back up as part of a repair scheme.
- Where a thin structural lining is wanted against an excavated or existing surface.
Professional review
Where additional professional review is especially important
These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.
- Anywhere it carries ground or structural load, without a design by a qualified engineer.
- Where the finished appearance must be smooth and regular without a separate applied finish.
- In confined or occupied spaces where dust, rebound and overspray cannot be controlled.
- Where the receiving surface is loose, contaminated or saturated and has not been prepared.
- Where the crew's nozzle experience with the specific process has not been established.
Properties
Key properties to discuss
Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.
- Installation dependency
- Quality is made at the nozzle. Angle, distance, layer thickness and the sequence of passes all sit with the operator, which makes crew experience with the chosen process a more decisive factor here than it is with poured concrete.
- Substrate dependency
- The receiving face governs adhesion. Loose material, contamination, standing water and running seepage all interfere with bond, so surface preparation and water control come before any spraying begins rather than after it.
- Moisture behaviour
- Sprayed linings are often used where water is present in the ground, but managing that water is a designed function of the wider scheme, involving drainage, membranes and detailing rather than the sprayed layer working alone.
- Repairability
- Because the method builds in layers, later repairs can usually be sprayed or hand-applied onto a prepared face, though matching texture and colour to the surrounding work is rarely straightforward.
- Appearance
- As-sprayed surfaces are undulating and textured. Where a flatter face is wanted, it is cut, screeded or trowelled as a separate operation, or covered by a subsequent lining or applied finish.
- Documentation
- The mix design, any fibres or admixtures, the nozzle process used and the layer sequence are all worth recording, because the completed lining cannot be inspected internally once it has been built up.
Exposure
Exposure and environmental conditions
- Is groundwater or seepage present at the face, and how is it intercepted before spraying?
- What temperature and humidity conditions will apply during spraying and during curing?
- Will the finished surface remain buried out of sight, or be exposed within an occupied space?
- How will dust and rebound be contained, particularly in enclosed or occupied buildings?
- Is the face subject to ground movement, vibration or nearby excavation during the works?
Assembly
Substrate and system dependencies
What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.
- How the receiving face is cleaned, trimmed and prepared before the first pass is applied.
- Whether mesh, bars or fibres provide reinforcement, and how they are held clear of the face.
- How drainage behind the lining is arranged, and which party is responsible for providing it.
- How the lining ties into adjoining structure, slabs, walls and previously sprayed panels.
- Where construction joints between panels and lifts fall, and how those joints are prepared.
Appearance
Appearance and finish considerations
- The natural finish is textured and uneven, which suits buried and utilitarian surfaces well.
- A flat face requires a separate screeded, trowelled or applied finish as an added operation.
- Colour follows the mix and varies visibly between batches and between days of work.
- Fibres, where used, may show at the surface unless a finishing layer is applied over them.
Durability
Durability questions
Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.
- How is the lining designed to behave over time, and who has carried out that design?
- How will layer bond and layer thickness be checked as the work proceeds?
- What is the plan where water finds its way behind the lining after completion?
- How does the surrounding ground or structure move, and what does that mean for the lining?
- What curing regime is proposed, given that thin sprayed layers dry out quickly?
Upkeep
Maintenance and repair considerations
- How would damage or delamination be identified once the lining is finished and in place?
- Can areas be cut out and re-sprayed without disturbing the adjoining completed work?
- Who is responsible for inspecting the lining periodically, and on what basis?
- Are records kept of panel sequence and mix so that later repairs can be matched?
Installation
Installation dependencies
What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.
- The choice between wet and dry process, which changes plant, crew and site logistics.
- Nozzle operator experience with the specific process and with this type of work.
- Access for plant, hoses and material delivery to the working face during spraying.
- Control of rebound, overspray and dust, and disposal of the material that falls away.
- Sequencing of excavation, support and spraying, which is set by the engineering design.
- Curing and protection of freshly sprayed layers before subsequent passes are applied.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The engineer's design and sequence drawings for the sprayed works on this project.
- The mix design used, including any fibres and admixtures that it contains.
- A record of which process was used, and of the panel and layer sequencing.
- The contractor's method for controlling water at the face during spraying.
- Any records kept of thickness checks and of the crew carrying out the work.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Who has designed the sprayed element, and what exactly is it being asked to do?
- Is the wet or the dry process proposed here, and what is the reason for that choice?
- What experience does the nozzle crew have with this process and this type of work?
- How is water at the face being intercepted and drained before and after spraying?
- Is reinforcement mesh, bar, fibre or a combination, and how will it be encased?
- How will layer thickness and bond be checked while the work is still in progress?
- What finish will the exposed face have, and is a separate finishing layer included?
- How will rebound and dust be contained and removed from the site during works?
Blind spots
Commonly overlooked points
- Sprayed concrete is a placement method, so most of the quality is decided by the crew rather than the ticket.
- Rebound is material that leaves the face, and it has to be collected and disposed of.
- Reinforcement can shadow the spray, leaving voids behind bars where technique is wrong.
- The as-sprayed surface is textured, and a smooth face is an extra operation rather than a default.
- Water arriving at the face is a design problem to solve before spraying, not during it.
What this page does not do
- Sprayed concrete used in ground support, retaining or structural work is designed by a qualified engineer, and its adequacy cannot be judged from a reference page.
- Whether an assembly keeps water out depends on the whole scheme of drainage, membranes and detailing, and not on the sprayed layer alone.
- This entry describes the method in general terms and is not a method statement; spraying involves plant, dust and rebound that trained crews manage under their own procedures.
- Requirements for excavation, temporary support and sequencing vary by location and must be confirmed with the relevant authority and the project engineer.
Related entries
Related materials
Materials from the same family, an adjacent role in the assembly, or a shared application.
Inspiration
Related Ideas Library pages
Design directions where this material commonly appears.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this material comes up.
Go deeper
Related Build Design Hub guides
Planning guidance and neutral comparisons behind the decisions on this page.
Concrete & Cement Materials
Reference entries for cement-based materials — ready-mixed and precast concrete, screeds, levelling compounds, renders of the cementitious family and the admixtures that modify them.
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