Shotcrete is concrete or mortar that is conveyed through a hose and pneumatically projected at high velocity onto a surface. Because the material leaves the nozzle under such force, it is placed and compacted in one single operation — there is no separate pouring and vibrating step as with conventional cast-in-place concrete. The American Concrete Institute (ACI) uses essentially the same definition, describing shotcrete as mortar or concrete pneumatically projected at high velocity onto a surface.
For engineers and contractors choosing between placement methods, the defining question is not whether shotcrete is "concrete" or "mortar" in a strict sense, but how and where the water is introduced into the mix. That single variable separates the two established application processes — dry-mix and wet-mix — and determines handling, equipment and site conditions.
What distinguishes the dry process from the wet process?
The two shotcrete application methods differ primarily in the point at which water is added to the mixture:
Dry process: Dry ingredients are loaded into a hopper and pneumatically conveyed through a hose to the nozzle. The nozzle operator adds water only at the nozzle itself, so the water and the dry mix are not fully combined until the material actually strikes the receiving surface.
Wet process: An already prepared concrete mix — typically ready-mixed concrete — is pumped to the nozzle, where compressed air is introduced to propel the material and shape the spray pattern. In practical terms, the wet process starts with a fully batched, hydrated mix and uses compressed air only to accelerate and disperse it at the nozzle.
The dry process keeps the mix dehydrated until the very last moment, with final hydration happening in the hose-to-nozzle transition and at the point of impact.
Why does the point of water addition matter on site?
Because the dry process lets the nozzle operator control water content instantaneously at the point of application, it offers a practical advantage for overhead and vertical work: the operator can adjust the water-to-cement ratio on the fly to suit the application angle and surface condition, which supports effective placement without needing to change the batch upstream. This operator-level control is one reason dry-mix shotcrete remains common in applications where spray conditions vary across a single job — different wall angles, overhead sections and variable substrate absorbency within the same shift.
How does shotcrete relate to other concrete technologies?
Shotcrete is a placement method rather than a distinct concrete family — it can be based on conventional Portland cement mixes or on more specialised formulations. For structures requiring reinforcement, shotcrete is frequently combined with reinforcing steel or fibre reinforcement embedded in the sprayed layer, since the method itself governs placement and compaction rather than the reinforcement strategy.
